From 90e23f05216d6b7dbebc88c61b20edb8c6483968 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 10:09:25 -0500
Subject: [PATCH 01/23] feat: separate context propagation

---
 packages/opentelemetry-api/package.json       |  3 +
 .../src/context/propagation/HttpTextFormat.ts | 32 +++----
 .../context/propagation/NoopHttpTextFormat.ts | 13 +--
 .../src/context/propagation/carrier.ts        | 19 ++++
 .../distributed_context/DistributedContext.ts | 29 ------
 .../src/distributed_context/EntryValue.ts     | 45 ---------
 packages/opentelemetry-api/src/index.ts       | 21 ++--
 .../src/metrics/BoundInstrument.ts            |  9 +-
 .../opentelemetry-api/src/metrics/Metric.ts   | 14 +--
 .../src/metrics/NoopMeter.ts                  | 20 +---
 .../noop-implementations/noop-tracer.test.ts  |  6 +-
 packages/opentelemetry-core/package.json      |  1 +
 .../opentelemetry-core/src/context/context.ts | 81 ++++++++++++++++
 .../src/context/propagation/B3Format.ts       | 25 +++--
 .../context/propagation/HttpTraceContext.ts   | 21 ++--
 packages/opentelemetry-core/src/index.ts      |  1 +
 .../test/context/B3Format.test.ts             | 91 +++++++++++++-----
 .../test/context/HttpTraceContext.test.ts     | 55 ++++++-----
 .../src/BoundInstrument.ts                    |  6 +-
 .../opentelemetry-plugin-http/src/http.ts     | 16 +++-
 .../test/utils/DummyPropagation.ts            | 17 ++--
 .../test/utils/DummyPropagation.ts            | 17 ++--
 .../src/xhr.ts                                |  6 +-
 .../package.json                              |  3 +-
 .../src/JaegerHttpTraceFormat.ts              | 34 +++----
 .../test/JaegerHttpTraceFormat.test.ts        | 47 ++++++---
 .../src/AsyncHooksScopeManager.ts             | 20 ++--
 .../test/AsyncHooksScopeManager.test.ts       | 55 ++++++-----
 .../src/NoopScopeManager.ts                   |  9 +-
 .../opentelemetry-scope-base/src/context.ts   | 74 ++++++++++++++
 .../opentelemetry-scope-base/src/index.ts     |  1 +
 .../opentelemetry-scope-base/src/types.ts     |  8 +-
 .../test/NoopScopeManager.test.ts             | 20 ++--
 .../src/ZoneScopeManager.ts                   | 41 ++++----
 .../test/ZoneScopeManager.test.ts             | 96 ++++++++++++-------
 .../src/shim.ts                               | 24 +++--
 packages/opentelemetry-tracing/src/Tracer.ts  | 22 +++--
 .../test/BasicTracerRegistry.test.ts          |  6 +-
 .../src/StackScopeManager.ts                  | 24 ++---
 .../test/StackScopeManager.test.ts            | 48 ++++++----
 40 files changed, 636 insertions(+), 444 deletions(-)
 create mode 100644 packages/opentelemetry-api/src/context/propagation/carrier.ts
 delete mode 100644 packages/opentelemetry-api/src/distributed_context/DistributedContext.ts
 delete mode 100644 packages/opentelemetry-api/src/distributed_context/EntryValue.ts
 create mode 100644 packages/opentelemetry-core/src/context/context.ts
 create mode 100644 packages/opentelemetry-scope-base/src/context.ts

diff --git a/packages/opentelemetry-api/package.json b/packages/opentelemetry-api/package.json
index 5d5cc4218e..d640ed3c9b 100644
--- a/packages/opentelemetry-api/package.json
+++ b/packages/opentelemetry-api/package.json
@@ -45,6 +45,9 @@
   "publishConfig": {
     "access": "public"
   },
+  "dependencies": {
+    "@opentelemetry/scope-base": "^0.4.0"
+  },
   "devDependencies": {
     "@types/mocha": "^5.2.7",
     "@types/node": "^12.6.8",
diff --git a/packages/opentelemetry-api/src/context/propagation/HttpTextFormat.ts b/packages/opentelemetry-api/src/context/propagation/HttpTextFormat.ts
index c3cf8c314e..fef9293ecf 100644
--- a/packages/opentelemetry-api/src/context/propagation/HttpTextFormat.ts
+++ b/packages/opentelemetry-api/src/context/propagation/HttpTextFormat.ts
@@ -14,39 +14,35 @@
  * limitations under the License.
  */
 
-import { SpanContext } from '../../trace/span_context';
+import { Context } from '@opentelemetry/scope-base';
+import { Carrier } from './carrier';
 
 /**
- * Injects and extracts a value as text into carriers that travel in-band
- * across process boundaries. Encoding is expected to conform to the HTTP
+ * Injects {@link Context} into and extracts it from carriers that travel
+ * in-band across process boundaries. Encoding is expected to conform to the HTTP
  * Header Field semantics. Values are often encoded as RPC/HTTP request headers.
  *
  * The carrier of propagated data on both the client (injector) and server
- * (extractor) side is usually an http request. Propagation is usually
- * implemented via library- specific request interceptors, where the
- * client-side injects values and the server-side extracts them.
+ * (extractor) side is usually an object such as http headers.
  */
 export interface HttpTextFormat {
   /**
-   * Injects the given {@link SpanContext} instance to transmit over the wire.
+   * Injects values from a given {@link Context} into a carrier.
    *
    * OpenTelemetry defines a common set of format values (BinaryFormat and
    * HTTPTextFormat), and each has an expected `carrier` type.
    *
-   * @param spanContext the SpanContext to transmit over the wire.
-   * @param format the format of the carrier.
-   * @param carrier the carrier of propagation fields, such as an http request.
+   * @param context the Context from which to extract values to transmit over the wire.
+   * @param carrier the carrier of propagation fields, such as http request headers.
    */
-  inject(spanContext: SpanContext, format: string, carrier: unknown): void;
+  inject(context: Context, carrier: Carrier): void;
 
   /**
-   * Returns a {@link SpanContext} instance extracted from `carrier` in the
-   * given format from upstream.
+   * Given a {@link Context} and a carrier, extract context values from a carrier and
+   * return a new context, created from the old context, with the extracted values.
    *
-   * @param format the format of the carrier.
-   * @param carrier the carrier of propagation fields, such as an http request.
-   * @returns SpanContext The extracted SpanContext, or null if no such
-   *     SpanContext could be found in carrier.
+   * @param context the Context from which to extract values to transmit over the wire.
+   * @param carrier the carrier of propagation fields, such as http request headers.
    */
-  extract(format: string, carrier: unknown): SpanContext | null;
+  extract(context: Context, carrier: Carrier): Context;
 }
diff --git a/packages/opentelemetry-api/src/context/propagation/NoopHttpTextFormat.ts b/packages/opentelemetry-api/src/context/propagation/NoopHttpTextFormat.ts
index 7596dd96b3..1f38729eb5 100644
--- a/packages/opentelemetry-api/src/context/propagation/NoopHttpTextFormat.ts
+++ b/packages/opentelemetry-api/src/context/propagation/NoopHttpTextFormat.ts
@@ -14,18 +14,19 @@
  * limitations under the License.
  */
 
-import { SpanContext } from '../../trace/span_context';
+import { Context } from '@opentelemetry/scope-base';
+import { Carrier } from './carrier';
 import { HttpTextFormat } from './HttpTextFormat';
 
 /**
  * No-op implementations of {@link HttpTextFormat}.
  */
 export class NoopHttpTextFormat implements HttpTextFormat {
-  // By default does nothing
-  inject(spanContext: SpanContext, format: string, carrier: unknown): void {}
-  // By default does nothing
-  extract(format: string, carrier: unknown): SpanContext | null {
-    return null;
+  /** Noop inject function does nothing */
+  inject(context: Context, carrier: Carrier): void {}
+  /** Noop extract function does nothing and returns the input context */
+  extract(context: Context, carrier: Carrier): Context {
+    return context;
   }
 }
 
diff --git a/packages/opentelemetry-api/src/context/propagation/carrier.ts b/packages/opentelemetry-api/src/context/propagation/carrier.ts
new file mode 100644
index 0000000000..7644ace1af
--- /dev/null
+++ b/packages/opentelemetry-api/src/context/propagation/carrier.ts
@@ -0,0 +1,19 @@
+/*!
+ * Copyright 2020, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export type Carrier = {
+  [key: string]: unknown;
+};
diff --git a/packages/opentelemetry-api/src/distributed_context/DistributedContext.ts b/packages/opentelemetry-api/src/distributed_context/DistributedContext.ts
deleted file mode 100644
index b06dcb8059..0000000000
--- a/packages/opentelemetry-api/src/distributed_context/DistributedContext.ts
+++ /dev/null
@@ -1,29 +0,0 @@
-/*!
- * Copyright 2019, OpenTelemetry Authors
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-import { EntryValue } from './EntryValue';
-
-/**
- * DistributedContext represents collection of entries. Each key of
- * DistributedContext is associated with exactly one value. DistributedContext
- * is serializable, to facilitate propagating it not only inside the process
- * but also across process boundaries. DistributedContext is used to annotate
- * telemetry with the name:value pair Entry. Those values can be used to add
- * dimension to the metric or additional contest properties to logs and traces.
- */
-export interface DistributedContext {
-  [entryKey: string]: EntryValue;
-}
diff --git a/packages/opentelemetry-api/src/distributed_context/EntryValue.ts b/packages/opentelemetry-api/src/distributed_context/EntryValue.ts
deleted file mode 100644
index cb0c58557e..0000000000
--- a/packages/opentelemetry-api/src/distributed_context/EntryValue.ts
+++ /dev/null
@@ -1,45 +0,0 @@
-/*!
- * Copyright 2019, OpenTelemetry Authors
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-/**
- * {@link EntryValue} contains properties associated with a {@link
- * DistributedContext}.
- */
-export interface EntryValue {
-  /** `String` value of the `EntryValue`. */
-  value: string;
-  /**
-   * ttl is an integer that represents number of hops an entry can
-   * propagate.
-   */
-  ttl?: EntryTtl;
-}
-
-/**
- * EntryTtl is an integer that represents number of hops an entry can propagate.
- *
- * For now, ONLY special values (0 and -1) are supported.
- */
-export enum EntryTtl {
-  /**
-   * NO_PROPAGATION is considered to have local scope and is used within the
-   * process it created.
-   */
-  NO_PROPAGATION = 0,
-
-  /** UNLIMITED_PROPAGATION can propagate unlimited hops. */
-  UNLIMITED_PROPAGATION = -1,
-}
diff --git a/packages/opentelemetry-api/src/index.ts b/packages/opentelemetry-api/src/index.ts
index ab10bb7ed4..49a1d42e48 100644
--- a/packages/opentelemetry-api/src/index.ts
+++ b/packages/opentelemetry-api/src/index.ts
@@ -17,33 +17,32 @@
 export * from './common/Logger';
 export * from './common/Time';
 export * from './context/propagation/BinaryFormat';
+export * from './context/propagation/carrier';
 export * from './context/propagation/HttpTextFormat';
-export * from './distributed_context/DistributedContext';
-export * from './distributed_context/EntryValue';
 export * from './metrics/BoundInstrument';
 export * from './metrics/Meter';
 export * from './metrics/MeterProvider';
 export * from './metrics/Metric';
+export * from './metrics/NoopMeter';
+export * from './metrics/NoopMeterProvider';
 export * from './trace/attributes';
 export * from './trace/Event';
 export * from './trace/instrumentation/Plugin';
 export * from './trace/link';
+export * from './trace/NoopSpan';
+export * from './trace/NoopTracer';
+export * from './trace/NoopTracerProvider';
 export * from './trace/Sampler';
-export * from './trace/span';
-export * from './trace/SpanOptions';
 export * from './trace/span_context';
 export * from './trace/span_kind';
+export * from './trace/span';
+export * from './trace/SpanOptions';
 export * from './trace/status';
 export * from './trace/TimedEvent';
-export * from './trace/tracer';
-export * from './trace/tracer_provider';
 export * from './trace/trace_flags';
 export * from './trace/trace_state';
-export * from './trace/NoopSpan';
-export * from './trace/NoopTracer';
-export * from './trace/NoopTracerProvider';
-export * from './metrics/NoopMeterProvider';
-export * from './metrics/NoopMeter';
+export * from './trace/tracer_provider';
+export * from './trace/tracer';
 
 import { TraceAPI } from './api/trace';
 /** Entrypoint for trace API */
diff --git a/packages/opentelemetry-api/src/metrics/BoundInstrument.ts b/packages/opentelemetry-api/src/metrics/BoundInstrument.ts
index 83612d6b4d..284f6e4a8c 100644
--- a/packages/opentelemetry-api/src/metrics/BoundInstrument.ts
+++ b/packages/opentelemetry-api/src/metrics/BoundInstrument.ts
@@ -14,7 +14,6 @@
  * limitations under the License.
  */
 
-import { DistributedContext } from '../distributed_context/DistributedContext';
 import { SpanContext } from '../trace/span_context';
 
 /** An Instrument for Counter Metric. */
@@ -40,15 +39,9 @@ export interface BoundMeasure {
   /**
    * Records the given value to this measure.
    * @param value the measurement to record.
-   * @param distContext the distContext associated with the measurements.
    * @param spanContext the {@link SpanContext} that identifies the {@link Span}
    *     for which the measurements are associated with.
    */
   record(value: number): void;
-  record(value: number, distContext: DistributedContext): void;
-  record(
-    value: number,
-    distContext: DistributedContext,
-    spanContext: SpanContext
-  ): void;
+  record(value: number, spanContext: SpanContext): void;
 }
diff --git a/packages/opentelemetry-api/src/metrics/Metric.ts b/packages/opentelemetry-api/src/metrics/Metric.ts
index 0c6ca61a70..d35da4fa7c 100644
--- a/packages/opentelemetry-api/src/metrics/Metric.ts
+++ b/packages/opentelemetry-api/src/metrics/Metric.ts
@@ -14,7 +14,6 @@
  * limitations under the License.
  */
 
-import { DistributedContext } from '../distributed_context/DistributedContext';
 import { SpanContext } from '../trace/span_context';
 
 /**
@@ -123,18 +122,7 @@ export interface MetricUtils {
    */
   record(value: number, labelSet: LabelSet): void;
 
-  record(
-    value: number,
-    labelSet: LabelSet,
-    distContext: DistributedContext
-  ): void;
-
-  record(
-    value: number,
-    labelSet: LabelSet,
-    distContext: DistributedContext,
-    spanContext: SpanContext
-  ): void;
+  record(value: number, labelSet: LabelSet, spanContext: SpanContext): void;
 }
 
 /**
diff --git a/packages/opentelemetry-api/src/metrics/NoopMeter.ts b/packages/opentelemetry-api/src/metrics/NoopMeter.ts
index c39a664aa5..0c3ecfce26 100644
--- a/packages/opentelemetry-api/src/metrics/NoopMeter.ts
+++ b/packages/opentelemetry-api/src/metrics/NoopMeter.ts
@@ -17,7 +17,6 @@
 import { Meter } from './Meter';
 import { MetricOptions, Metric, Labels, LabelSet, MetricUtils } from './Metric';
 import { BoundMeasure, BoundCounter, BoundGauge } from './BoundInstrument';
-import { DistributedContext } from '../distributed_context/DistributedContext';
 import { SpanContext } from '../trace/span_context';
 
 /**
@@ -119,18 +118,11 @@ export class NoopGaugeMetric extends NoopMetric<BoundGauge>
 
 export class NoopMeasureMetric extends NoopMetric<BoundMeasure>
   implements Pick<MetricUtils, 'record'> {
-  record(
-    value: number,
-    labelSet: LabelSet,
-    distContext?: DistributedContext,
-    spanContext?: SpanContext
-  ) {
-    if (typeof distContext === 'undefined') {
+  record(value: number, labelSet: LabelSet, spanContext?: SpanContext) {
+    if (typeof spanContext === 'undefined') {
       this.bind(labelSet).record(value);
-    } else if (typeof spanContext === 'undefined') {
-      this.bind(labelSet).record(value, distContext);
     } else {
-      this.bind(labelSet).record(value, distContext, spanContext);
+      this.bind(labelSet).record(value, spanContext);
     }
   }
 }
@@ -148,11 +140,7 @@ export class NoopBoundGauge implements BoundGauge {
 }
 
 export class NoopBoundMeasure implements BoundMeasure {
-  record(
-    value: number,
-    distContext?: DistributedContext,
-    spanContext?: SpanContext
-  ): void {
+  record(value: number, spanContext?: SpanContext): void {
     return;
   }
 }
diff --git a/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts b/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts
index 32dd6813ed..9fd5171dbd 100644
--- a/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts
+++ b/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts
@@ -16,6 +16,7 @@
 
 import * as assert from 'assert';
 import { NoopTracer, NOOP_SPAN, SpanKind } from '../../src';
+import { Context } from '@opentelemetry/scope-base';
 
 describe('NoopTracer', () => {
   it('should not crash', () => {
@@ -38,8 +39,9 @@ describe('NoopTracer', () => {
     assert.deepStrictEqual(tracer.getCurrentSpan(), NOOP_SPAN);
     const httpTextFormat = tracer.getHttpTextFormat();
     assert.ok(httpTextFormat);
-    httpTextFormat.inject(spanContext, 'HttpTextFormat', {});
-    assert.deepStrictEqual(httpTextFormat.extract('HttpTextFormat', {}), null);
+
+    httpTextFormat.inject(Context.ROOT_CONTEXT, {});
+    assert.deepStrictEqual(httpTextFormat.extract(Context.ROOT_CONTEXT, {}), Context.ROOT_CONTEXT);
 
     const binaryFormat = tracer.getBinaryFormat();
     assert.ok(binaryFormat);
diff --git a/packages/opentelemetry-core/package.json b/packages/opentelemetry-core/package.json
index 42a02a24e6..ae59461fc8 100644
--- a/packages/opentelemetry-core/package.json
+++ b/packages/opentelemetry-core/package.json
@@ -79,6 +79,7 @@
   },
   "dependencies": {
     "@opentelemetry/api": "^0.4.0",
+    "@opentelemetry/scope-base": "^0.4.0",
     "semver": "^6.3.0"
   }
 }
diff --git a/packages/opentelemetry-core/src/context/context.ts b/packages/opentelemetry-core/src/context/context.ts
new file mode 100644
index 0000000000..b404664423
--- /dev/null
+++ b/packages/opentelemetry-core/src/context/context.ts
@@ -0,0 +1,81 @@
+/*!
+ * Copyright 2020, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { Span, SpanContext } from '@opentelemetry/api';
+import { Context as ContextBase } from '@opentelemetry/scope-base';
+
+/**
+ * Context class with static helper functions for accessing values
+ * of cross-cutting concerns.
+ */
+export class Context extends ContextBase {
+  /**
+   * Return the active span if one exists
+   *
+   * @param context context to get span from
+   */
+  static getActiveSpan(context: Context): Span | undefined {
+    return (context.getValue('ACTIVE_SPAN') as Span) || undefined;
+  }
+
+  /**
+   * Set the active span on a context
+   *
+   * @param context context to use as parent
+   * @param span span to set active
+   */
+  static setActiveSpan(context: Context, span: Span): Context {
+    return context.setValue('ACTIVE_SPAN', span);
+  }
+
+  /**
+   * Get the extracted span context from a context
+   *
+   * @param context context to get span context from
+   */
+  static getExtractedSpanContext(context: Context): SpanContext | undefined {
+    return (
+      (context.getValue('EXTRACTED_SPAN_CONTEXT') as SpanContext) || undefined
+    );
+  }
+
+  /**
+   * Set the extracted span context on a context
+   *
+   * @param context context to set span context on
+   * @param spanContext span context to set
+   */
+  static setExtractedSpanContext(
+    context: Context,
+    spanContext: SpanContext
+  ): Context {
+    return context.setValue('EXTRACTED_SPAN_CONTEXT', spanContext);
+  }
+
+  /**
+   * Get the span context of the parent span if it exists,
+   * or the extracted span context if there is no active
+   * span.
+   *
+   * @param context context to get values from
+   */
+  static getParentSpanContext(context: Context) {
+    return (
+      Context.getActiveSpan(context)?.context() ||
+      Context.getExtractedSpanContext(context)
+    );
+  }
+}
diff --git a/packages/opentelemetry-core/src/context/propagation/B3Format.ts b/packages/opentelemetry-core/src/context/propagation/B3Format.ts
index 2363edc3c7..5b3db96594 100644
--- a/packages/opentelemetry-core/src/context/propagation/B3Format.ts
+++ b/packages/opentelemetry-core/src/context/propagation/B3Format.ts
@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import { SpanContext, HttpTextFormat, TraceFlags } from '@opentelemetry/api';
+import { HttpTextFormat, TraceFlags } from '@opentelemetry/api';
+import { Context } from '../context';
 
 export const X_B3_TRACE_ID = 'x-b3-traceid';
 export const X_B3_SPAN_ID = 'x-b3-spanid';
@@ -36,11 +37,10 @@ function isValidSpanId(spanId: string): boolean {
  * Based on: https://github.com/openzipkin/b3-propagation
  */
 export class B3Format implements HttpTextFormat {
-  inject(
-    spanContext: SpanContext,
-    format: string,
-    carrier: { [key: string]: unknown }
-  ): void {
+  inject(context: Context, carrier: { [key: string]: unknown }) {
+    const spanContext = Context.getParentSpanContext(context);
+    if (!spanContext) return;
+
     if (
       isValidTraceId(spanContext.traceId) &&
       isValidSpanId(spanContext.spanId)
@@ -56,14 +56,11 @@ export class B3Format implements HttpTextFormat {
     }
   }
 
-  extract(
-    format: string,
-    carrier: { [key: string]: unknown }
-  ): SpanContext | null {
+  extract(context: Context, carrier: { [key: string]: unknown }): Context {
     const traceIdHeader = carrier[X_B3_TRACE_ID];
     const spanIdHeader = carrier[X_B3_SPAN_ID];
     const sampledHeader = carrier[X_B3_SAMPLED];
-    if (!traceIdHeader || !spanIdHeader) return null;
+    if (!traceIdHeader || !spanIdHeader) return context;
     const traceId = Array.isArray(traceIdHeader)
       ? traceIdHeader[0]
       : traceIdHeader;
@@ -73,15 +70,15 @@ export class B3Format implements HttpTextFormat {
       : sampledHeader;
 
     if (isValidTraceId(traceId) && isValidSpanId(spanId)) {
-      return {
+      return Context.setExtractedSpanContext(context, {
         traceId,
         spanId,
         isRemote: true,
         traceFlags: isNaN(Number(options))
           ? TraceFlags.UNSAMPLED
           : Number(options),
-      };
+      });
     }
-    return null;
+    return context;
   }
 }
diff --git a/packages/opentelemetry-core/src/context/propagation/HttpTraceContext.ts b/packages/opentelemetry-core/src/context/propagation/HttpTraceContext.ts
index cf9860014f..fa70fbe1d2 100644
--- a/packages/opentelemetry-core/src/context/propagation/HttpTraceContext.ts
+++ b/packages/opentelemetry-core/src/context/propagation/HttpTraceContext.ts
@@ -16,6 +16,7 @@
 
 import { HttpTextFormat, SpanContext, TraceFlags } from '@opentelemetry/api';
 import { TraceState } from '../../trace/TraceState';
+import { Context } from '../context';
 
 export const TRACE_PARENT_HEADER = 'traceparent';
 export const TRACE_STATE_HEADER = 'tracestate';
@@ -56,11 +57,10 @@ export function parseTraceParent(traceParent: string): SpanContext | null {
  * https://www.w3.org/TR/trace-context/
  */
 export class HttpTraceContext implements HttpTextFormat {
-  inject(
-    spanContext: SpanContext,
-    format: string,
-    carrier: { [key: string]: unknown }
-  ) {
+  inject(context: Context, carrier: { [key: string]: unknown }) {
+    const spanContext = Context.getParentSpanContext(context);
+    if (!spanContext) return;
+
     const traceParent = `${VERSION}-${spanContext.traceId}-${
       spanContext.spanId
     }-0${Number(spanContext.traceFlags || TraceFlags.UNSAMPLED).toString(16)}`;
@@ -71,17 +71,14 @@ export class HttpTraceContext implements HttpTextFormat {
     }
   }
 
-  extract(
-    format: string,
-    carrier: { [key: string]: unknown }
-  ): SpanContext | null {
+  extract(context: Context, carrier: { [key: string]: unknown }): Context {
     const traceParentHeader = carrier[TRACE_PARENT_HEADER];
-    if (!traceParentHeader) return null;
+    if (!traceParentHeader) return context;
     const traceParent = Array.isArray(traceParentHeader)
       ? traceParentHeader[0]
       : traceParentHeader;
     const spanContext = parseTraceParent(traceParent);
-    if (!spanContext) return null;
+    if (!spanContext) return context;
 
     spanContext.isRemote = true;
 
@@ -94,6 +91,6 @@ export class HttpTraceContext implements HttpTextFormat {
         : traceStateHeader;
       spanContext.traceState = new TraceState(state as string);
     }
-    return spanContext;
+    return Context.setExtractedSpanContext(context, spanContext);
   }
 }
diff --git a/packages/opentelemetry-core/src/index.ts b/packages/opentelemetry-core/src/index.ts
index f1d0611e27..3038ce0b95 100644
--- a/packages/opentelemetry-core/src/index.ts
+++ b/packages/opentelemetry-core/src/index.ts
@@ -19,6 +19,7 @@ export * from './common/NoopLogger';
 export * from './common/time';
 export * from './common/types';
 export * from './version';
+export * from './context/context';
 export * from './context/propagation/B3Format';
 export * from './context/propagation/BinaryTraceContext';
 export * from './context/propagation/HttpTraceContext';
diff --git a/packages/opentelemetry-core/test/context/B3Format.test.ts b/packages/opentelemetry-core/test/context/B3Format.test.ts
index 97087e076a..ea352f24cc 100644
--- a/packages/opentelemetry-core/test/context/B3Format.test.ts
+++ b/packages/opentelemetry-core/test/context/B3Format.test.ts
@@ -14,14 +14,15 @@
  * limitations under the License.
  */
 
+import { SpanContext, TraceFlags } from '@opentelemetry/api';
 import * as assert from 'assert';
+import { Context } from '../../src/context/context';
 import {
   B3Format,
-  X_B3_TRACE_ID,
-  X_B3_SPAN_ID,
   X_B3_SAMPLED,
+  X_B3_SPAN_ID,
+  X_B3_TRACE_ID,
 } from '../../src/context/propagation/B3Format';
-import { SpanContext, TraceFlags } from '@opentelemetry/api';
 import { TraceState } from '../../src/trace/TraceState';
 
 describe('B3Format', () => {
@@ -40,7 +41,10 @@ describe('B3Format', () => {
         traceFlags: TraceFlags.SAMPLED,
       };
 
-      b3Format.inject(spanContext, 'B3Format', carrier);
+      b3Format.inject(
+        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        carrier
+      );
       assert.deepStrictEqual(
         carrier[X_B3_TRACE_ID],
         'd4cda95b652f4a1592b449d5929fda1b'
@@ -58,7 +62,10 @@ describe('B3Format', () => {
         isRemote: false,
       };
 
-      b3Format.inject(spanContext, 'B3Format', carrier);
+      b3Format.inject(
+        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        carrier
+      );
       assert.deepStrictEqual(
         carrier[X_B3_TRACE_ID],
         'd4cda95b652f4a1592b449d5929fda1b'
@@ -72,7 +79,10 @@ describe('B3Format', () => {
         traceId: '',
         spanId: '',
       };
-      b3Format.inject(emptySpanContext, 'B3Format', carrier);
+      b3Format.inject(
+        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, emptySpanContext),
+        carrier
+      );
       assert.deepStrictEqual(carrier[X_B3_TRACE_ID], undefined);
       assert.deepStrictEqual(carrier[X_B3_SPAN_ID], undefined);
     });
@@ -83,7 +93,10 @@ describe('B3Format', () => {
         spanId: '6e0c63257de34c92',
       };
 
-      b3Format.inject(spanContext, 'B3Format', carrier);
+      b3Format.inject(
+        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        carrier
+      );
       assert.deepStrictEqual(
         carrier[X_B3_TRACE_ID],
         'd4cda95b652f4a1592b449d5929fda1b'
@@ -97,7 +110,9 @@ describe('B3Format', () => {
     it('should extract context of a unsampled span from carrier', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
-      const extractedSpanContext = b3Format.extract('B3Format', carrier);
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        b3Format.extract(Context.ROOT_CONTEXT, carrier)
+      );
 
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: 'b7ad6b7169203331',
@@ -111,7 +126,9 @@ describe('B3Format', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
       carrier[X_B3_SAMPLED] = '1';
-      const extractedSpanContext = b3Format.extract('B3Format', carrier);
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        b3Format.extract(Context.ROOT_CONTEXT, carrier)
+      );
 
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: 'b7ad6b7169203331',
@@ -125,7 +142,9 @@ describe('B3Format', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
       carrier[X_B3_SAMPLED] = true;
-      const extractedSpanContext = b3Format.extract('B3Format', carrier);
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        b3Format.extract(Context.ROOT_CONTEXT, carrier)
+      );
 
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: 'b7ad6b7169203331',
@@ -139,7 +158,9 @@ describe('B3Format', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
       carrier[X_B3_SAMPLED] = false;
-      const extractedSpanContext = b3Format.extract('B3Format', carrier);
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        b3Format.extract(Context.ROOT_CONTEXT, carrier)
+      );
 
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: 'b7ad6b7169203331',
@@ -149,32 +170,54 @@ describe('B3Format', () => {
       });
     });
 
-    it('should return null when traceId is undefined', () => {
+    it('should return undefined when traceId is undefined', () => {
       carrier[X_B3_TRACE_ID] = undefined;
       carrier[X_B3_SPAN_ID] = undefined;
-      assert.deepStrictEqual(b3Format.extract('B3Format', carrier), null);
+      assert.deepStrictEqual(
+        Context.getExtractedSpanContext(
+          b3Format.extract(Context.ROOT_CONTEXT, carrier)
+        ),
+        undefined
+      );
     });
 
-    it('should return null when options and spanId are undefined', () => {
+    it('should return undefined when options and spanId are undefined', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = undefined;
-      assert.deepStrictEqual(b3Format.extract('B3Format', carrier), null);
+      assert.deepStrictEqual(
+        Context.getExtractedSpanContext(
+          b3Format.extract(Context.ROOT_CONTEXT, carrier)
+        ),
+        undefined
+      );
     });
 
-    it('returns null if b3 header is missing', () => {
-      assert.deepStrictEqual(b3Format.extract('B3Format', carrier), null);
+    it('returns undefined if b3 header is missing', () => {
+      assert.deepStrictEqual(
+        Context.getExtractedSpanContext(
+          b3Format.extract(Context.ROOT_CONTEXT, carrier)
+        ),
+        undefined
+      );
     });
 
-    it('returns null if b3 header is invalid', () => {
+    it('returns undefined if b3 header is invalid', () => {
       carrier[X_B3_TRACE_ID] = 'invalid!';
-      assert.deepStrictEqual(b3Format.extract('B3Format', carrier), null);
+      assert.deepStrictEqual(
+        Context.getExtractedSpanContext(
+          b3Format.extract(Context.ROOT_CONTEXT, carrier)
+        ),
+        undefined
+      );
     });
 
     it('extracts b3 from list of header', () => {
       carrier[X_B3_TRACE_ID] = ['0af7651916cd43dd8448eb211c80319c'];
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
       carrier[X_B3_SAMPLED] = '01';
-      const extractedSpanContext = b3Format.extract('B3Format', carrier);
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        b3Format.extract(Context.ROOT_CONTEXT, carrier)
+      );
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: 'b7ad6b7169203331',
         traceId: '0af7651916cd43dd8448eb211c80319c',
@@ -185,7 +228,7 @@ describe('B3Format', () => {
 
     it('should gracefully handle an invalid b3 header', () => {
       // A set of test cases with different invalid combinations of a
-      // b3 header. These should all result in a `null` SpanContext
+      // b3 header. These should all result in a `undefined` SpanContext
       // value being extracted.
 
       const testCases: Record<string, string> = {
@@ -223,8 +266,10 @@ describe('B3Format', () => {
       Object.getOwnPropertyNames(testCases).forEach(testCase => {
         carrier[X_B3_TRACE_ID] = testCases[testCase];
 
-        const extractedSpanContext = b3Format.extract('B3Format', carrier);
-        assert.deepStrictEqual(extractedSpanContext, null, testCase);
+        const extractedSpanContext = Context.getExtractedSpanContext(
+          b3Format.extract(Context.ROOT_CONTEXT, carrier)
+        );
+        assert.deepStrictEqual(extractedSpanContext, undefined, testCase);
       });
     });
   });
diff --git a/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts b/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts
index 28cbf335b4..83dccac40b 100644
--- a/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts
+++ b/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts
@@ -14,13 +14,14 @@
  * limitations under the License.
  */
 
+import { SpanContext, TraceFlags } from '@opentelemetry/api';
 import * as assert from 'assert';
+import { Context } from '../../src/context/context';
 import {
   HttpTraceContext,
   TRACE_PARENT_HEADER,
   TRACE_STATE_HEADER,
 } from '../../src/context/propagation/HttpTraceContext';
-import { SpanContext, TraceFlags } from '@opentelemetry/api';
 import { TraceState } from '../../src/trace/TraceState';
 
 describe('HttpTraceContext', () => {
@@ -39,7 +40,10 @@ describe('HttpTraceContext', () => {
         traceFlags: TraceFlags.SAMPLED,
       };
 
-      httpTraceContext.inject(spanContext, 'HttpTraceContext', carrier);
+      httpTraceContext.inject(
+        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        carrier
+      );
       assert.deepStrictEqual(
         carrier[TRACE_PARENT_HEADER],
         '00-d4cda95b652f4a1592b449d5929fda1b-6e0c63257de34c92-01'
@@ -55,7 +59,10 @@ describe('HttpTraceContext', () => {
         traceState: new TraceState('foo=bar,baz=qux'),
       };
 
-      httpTraceContext.inject(spanContext, '', carrier);
+      httpTraceContext.inject(
+        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        carrier
+      );
       assert.deepStrictEqual(
         carrier[TRACE_PARENT_HEADER],
         '00-d4cda95b652f4a1592b449d5929fda1b-6e0c63257de34c92-01'
@@ -64,13 +71,12 @@ describe('HttpTraceContext', () => {
     });
   });
 
-  describe('.extract()', () => {
+  describe('.extract())', () => {
     it('should extract context of a sampled span from carrier', () => {
       carrier[TRACE_PARENT_HEADER] =
         '00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01';
-      const extractedSpanContext = httpTraceContext.extract(
-        'HttpTraceContext',
-        carrier
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
       );
 
       assert.deepStrictEqual(extractedSpanContext, {
@@ -83,16 +89,20 @@ describe('HttpTraceContext', () => {
 
     it('returns null if traceparent header is missing', () => {
       assert.deepStrictEqual(
-        httpTraceContext.extract('HttpTraceContext', carrier),
-        null
+        Context.getExtractedSpanContext(
+          httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
+        ),
+        undefined
       );
     });
 
     it('returns null if traceparent header is invalid', () => {
       carrier[TRACE_PARENT_HEADER] = 'invalid!';
       assert.deepStrictEqual(
-        httpTraceContext.extract('HttpTraceContext', carrier),
-        null
+        Context.getExtractedSpanContext(
+          httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
+        ),
+        undefined
       );
     });
 
@@ -100,9 +110,8 @@ describe('HttpTraceContext', () => {
       carrier[TRACE_PARENT_HEADER] = [
         '00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01',
       ];
-      const extractedSpanContext = httpTraceContext.extract(
-        'HttpTraceContext',
-        carrier
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
       );
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: 'b7ad6b7169203331',
@@ -116,10 +125,10 @@ describe('HttpTraceContext', () => {
       carrier[TRACE_PARENT_HEADER] =
         '00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01';
       carrier[TRACE_STATE_HEADER] = 'foo=bar,baz=qux';
-      const extractedSpanContext = httpTraceContext.extract(
-        'HttpTraceContext',
-        carrier
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
       );
+
       assert.deepStrictEqual(
         extractedSpanContext!.traceState!.get('foo'),
         'bar'
@@ -134,9 +143,8 @@ describe('HttpTraceContext', () => {
       carrier[TRACE_PARENT_HEADER] =
         '00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01';
       carrier[TRACE_STATE_HEADER] = ['foo=bar,baz=qux', 'quux=quuz'];
-      const extractedSpanContext = httpTraceContext.extract(
-        'HttpTraceContext',
-        carrier
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
       );
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: 'b7ad6b7169203331',
@@ -187,11 +195,10 @@ describe('HttpTraceContext', () => {
       Object.getOwnPropertyNames(testCases).forEach(testCase => {
         carrier[TRACE_PARENT_HEADER] = testCases[testCase];
 
-        const extractedSpanContext = httpTraceContext.extract(
-          'HttpTraceContext',
-          carrier
+        const extractedSpanContext = Context.getExtractedSpanContext(
+          httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
         );
-        assert.deepStrictEqual(extractedSpanContext, null, testCase);
+        assert.deepStrictEqual(extractedSpanContext, undefined, testCase);
       });
     });
   });
diff --git a/packages/opentelemetry-metrics/src/BoundInstrument.ts b/packages/opentelemetry-metrics/src/BoundInstrument.ts
index b72176fae1..e78dca9576 100644
--- a/packages/opentelemetry-metrics/src/BoundInstrument.ts
+++ b/packages/opentelemetry-metrics/src/BoundInstrument.ts
@@ -144,11 +144,7 @@ export class BoundMeasure extends BaseBoundInstrument
     super(labelSet);
   }
 
-  record(
-    value: number,
-    distContext?: types.DistributedContext,
-    spanContext?: types.SpanContext
-  ): void {
+  record(value: number, spanContext?: types.SpanContext): void {
     if (this._disabled) return;
 
     if (this._absolute && value < 0) {
diff --git a/packages/opentelemetry-plugin-http/src/http.ts b/packages/opentelemetry-plugin-http/src/http.ts
index ee4c7f44ca..e2abb4e369 100644
--- a/packages/opentelemetry-plugin-http/src/http.ts
+++ b/packages/opentelemetry-plugin-http/src/http.ts
@@ -14,7 +14,6 @@
  * limitations under the License.
  */
 
-import { BasePlugin, isValid } from '@opentelemetry/core';
 import {
   CanonicalCode,
   Span,
@@ -22,6 +21,7 @@ import {
   SpanOptions,
   Status,
 } from '@opentelemetry/api';
+import { BasePlugin, Context, isValid } from '@opentelemetry/core';
 import {
   ClientRequest,
   IncomingMessage,
@@ -34,7 +34,6 @@ import * as semver from 'semver';
 import * as shimmer from 'shimmer';
 import * as url from 'url';
 import { AttributeNames } from './enums/AttributeNames';
-import { Format } from './enums/Format';
 import {
   Err,
   Func,
@@ -298,7 +297,11 @@ export class HttpPlugin extends BasePlugin<Http> {
         }),
       };
 
-      const spanContext = propagation.extract(Format.HTTP, headers);
+      // Using context direclty like this is temporary. In a future PR, context
+      // will be managed by the scope manager (which may be renamed to context manager?)
+      const spanContext = Context.getExtractedSpanContext(
+        propagation.extract(Context.ROOT_CONTEXT, headers)
+      );
       if (spanContext && isValid(spanContext)) {
         spanOptions.parent = spanContext;
       }
@@ -407,7 +410,12 @@ export class HttpPlugin extends BasePlugin<Http> {
       const span = plugin._startHttpSpan(operationName, spanOptions);
       plugin._tracer
         .getHttpTextFormat()
-        .inject(span.context(), Format.HTTP, options.headers);
+        // Using context direclty like this is temporary. In a future PR, context
+        // will be managed by the scope manager (which may be renamed to context manager?)
+        .inject(
+          Context.setActiveSpan(Context.ROOT_CONTEXT, span),
+          options.headers!
+        );
 
       const request: ClientRequest = plugin._safeExecute(
         span,
diff --git a/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts b/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts
index 3e4ca727fc..9101ab7d3c 100644
--- a/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts
+++ b/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts
@@ -13,23 +13,22 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import { SpanContext, HttpTextFormat } from '@opentelemetry/api';
+import { HttpTextFormat } from '@opentelemetry/api';
+import { Context } from '@opentelemetry/core';
 import * as http from 'http';
 
 export class DummyPropagation implements HttpTextFormat {
   static TRACE_CONTEXT_KEY = 'x-dummy-trace-id';
   static SPAN_CONTEXT_KEY = 'x-dummy-span-id';
-  extract(format: string, carrier: http.OutgoingHttpHeaders): SpanContext {
-    return {
+  extract(context: Context, carrier: http.OutgoingHttpHeaders) {
+    return Context.setExtractedSpanContext(Context.ROOT_CONTEXT, {
       traceId: carrier[DummyPropagation.TRACE_CONTEXT_KEY] as string,
       spanId: DummyPropagation.SPAN_CONTEXT_KEY,
-    };
+    });
   }
-  inject(
-    spanContext: SpanContext,
-    format: string,
-    headers: { [custom: string]: string }
-  ): void {
+  inject(context: Context, headers: { [custom: string]: string }): void {
+    const spanContext = Context.getParentSpanContext(context);
+    if (!spanContext) return;
     headers[DummyPropagation.TRACE_CONTEXT_KEY] = spanContext.traceId;
     headers[DummyPropagation.SPAN_CONTEXT_KEY] = spanContext.spanId;
   }
diff --git a/packages/opentelemetry-plugin-https/test/utils/DummyPropagation.ts b/packages/opentelemetry-plugin-https/test/utils/DummyPropagation.ts
index 3e4ca727fc..7bf3510ea7 100644
--- a/packages/opentelemetry-plugin-https/test/utils/DummyPropagation.ts
+++ b/packages/opentelemetry-plugin-https/test/utils/DummyPropagation.ts
@@ -13,23 +13,22 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import { SpanContext, HttpTextFormat } from '@opentelemetry/api';
+import { HttpTextFormat } from '@opentelemetry/api';
+import { Context } from '@opentelemetry/core';
 import * as http from 'http';
 
 export class DummyPropagation implements HttpTextFormat {
   static TRACE_CONTEXT_KEY = 'x-dummy-trace-id';
   static SPAN_CONTEXT_KEY = 'x-dummy-span-id';
-  extract(format: string, carrier: http.OutgoingHttpHeaders): SpanContext {
-    return {
+  extract(context: Context, carrier: http.OutgoingHttpHeaders) {
+    return Context.setExtractedSpanContext(context, {
       traceId: carrier[DummyPropagation.TRACE_CONTEXT_KEY] as string,
       spanId: DummyPropagation.SPAN_CONTEXT_KEY,
-    };
+    });
   }
-  inject(
-    spanContext: SpanContext,
-    format: string,
-    headers: { [custom: string]: string }
-  ): void {
+  inject(context: Context, headers: { [custom: string]: string }): void {
+    const spanContext = Context.getParentSpanContext(context);
+    if (!spanContext) return;
     headers[DummyPropagation.TRACE_CONTEXT_KEY] = spanContext.traceId;
     headers[DummyPropagation.SPAN_CONTEXT_KEY] = spanContext.spanId;
   }
diff --git a/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts b/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
index 3796dc4fa7..80c97c4ccf 100644
--- a/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
+++ b/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
@@ -16,6 +16,7 @@
 
 import {
   BasePlugin,
+  Context,
   hrTime,
   isUrlIgnored,
   isWrapped,
@@ -32,7 +33,6 @@ import {
 import * as shimmer from 'shimmer';
 import { AttributeNames } from './enums/AttributeNames';
 import { EventNames } from './enums/EventNames';
-import { Format } from './enums/Format';
 import {
   OpenFunction,
   PropagateTraceHeaderCorsUrls,
@@ -90,7 +90,9 @@ export class XMLHttpRequestPlugin extends BasePlugin<XMLHttpRequest> {
     const headers: { [key: string]: unknown } = {};
     this._tracer
       .getHttpTextFormat()
-      .inject(span.context(), Format.HTTP, headers);
+      // Using context direclty like this is temporary. In a future PR, context
+      // will be managed by the scope manager (which may be renamed to context manager?)
+      .inject(Context.setActiveSpan(Context.ROOT_CONTEXT, span), headers);
 
     Object.keys(headers).forEach(key => {
       xhr.setRequestHeader(key, String(headers[key]));
diff --git a/packages/opentelemetry-propagator-jaeger/package.json b/packages/opentelemetry-propagator-jaeger/package.json
index 565fe038ab..7cbe55f50b 100644
--- a/packages/opentelemetry-propagator-jaeger/package.json
+++ b/packages/opentelemetry-propagator-jaeger/package.json
@@ -70,6 +70,7 @@
     "webpack": "^4.35.2"
   },
   "dependencies": {
-    "@opentelemetry/api": "^0.4.0"
+    "@opentelemetry/api": "^0.4.0",
+    "@opentelemetry/core": "^0.4.0"
   }
 }
diff --git a/packages/opentelemetry-propagator-jaeger/src/JaegerHttpTraceFormat.ts b/packages/opentelemetry-propagator-jaeger/src/JaegerHttpTraceFormat.ts
index bcfd972492..6fb7c78b0a 100644
--- a/packages/opentelemetry-propagator-jaeger/src/JaegerHttpTraceFormat.ts
+++ b/packages/opentelemetry-propagator-jaeger/src/JaegerHttpTraceFormat.ts
@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import { SpanContext, HttpTextFormat, TraceFlags } from '@opentelemetry/api';
+import { HttpTextFormat, SpanContext, TraceFlags } from '@opentelemetry/api';
+import { Context } from '@opentelemetry/core';
 
 export const UBER_TRACE_ID_HEADER = 'uber-trace-id';
 
@@ -43,16 +44,10 @@ export class JaegerHttpTraceFormat implements HttpTextFormat {
     this._jaegerTraceHeader = customTraceHeader || UBER_TRACE_ID_HEADER;
   }
 
-  /**
-   * @param {SpanContext} spanContext - context from which we take information to inject in carrier.
-   * @param {string} format - unused.
-   * @param { [key: string]: unknown } carrier - a carrier to which span information will be injected.
-   **/
-  inject(
-    spanContext: SpanContext,
-    format: string,
-    carrier: { [key: string]: unknown }
-  ) {
+  inject(context: Context, carrier: { [key: string]: unknown }) {
+    const spanContext = Context.getParentSpanContext(context);
+    if (!spanContext) return;
+
     const traceFlags = `0${(
       spanContext.traceFlags || TraceFlags.UNSAMPLED
     ).toString(16)}`;
@@ -62,22 +57,17 @@ export class JaegerHttpTraceFormat implements HttpTextFormat {
     ] = `${spanContext.traceId}:${spanContext.spanId}:0:${traceFlags}`;
   }
 
-  /**
-   * @param {string} format - unused.
-   * @param { [key: string]: unknown } carrier - a carrier from which span context will be constructed.
-   * @return {SpanContext} - returns a span context extracted from carrier.
-   **/
-  extract(
-    format: string,
-    carrier: { [key: string]: unknown }
-  ): SpanContext | null {
+  extract(context: Context, carrier: { [key: string]: unknown }): Context {
     const uberTraceIdHeader = carrier[this._jaegerTraceHeader];
-    if (!uberTraceIdHeader) return null;
+    if (!uberTraceIdHeader) return context;
     const uberTraceId = Array.isArray(uberTraceIdHeader)
       ? uberTraceIdHeader[0]
       : uberTraceIdHeader;
 
-    return deserializeSpanContext(uberTraceId);
+    const spanContext = deserializeSpanContext(uberTraceId);
+    if (!spanContext) return context;
+
+    return Context.setExtractedSpanContext(context, spanContext);
   }
 }
 
diff --git a/packages/opentelemetry-propagator-jaeger/test/JaegerHttpTraceFormat.test.ts b/packages/opentelemetry-propagator-jaeger/test/JaegerHttpTraceFormat.test.ts
index 4e1ae9c9b6..f641ebdf6d 100644
--- a/packages/opentelemetry-propagator-jaeger/test/JaegerHttpTraceFormat.test.ts
+++ b/packages/opentelemetry-propagator-jaeger/test/JaegerHttpTraceFormat.test.ts
@@ -14,12 +14,13 @@
  * limitations under the License.
  */
 
+import { SpanContext, TraceFlags } from '@opentelemetry/api';
+import { Context } from '@opentelemetry/core';
 import * as assert from 'assert';
 import {
   JaegerHttpTraceFormat,
   UBER_TRACE_ID_HEADER,
 } from '../src/JaegerHttpTraceFormat';
-import { SpanContext, TraceFlags } from '@opentelemetry/api';
 
 describe('JaegerHttpTraceFormat', () => {
   const jaegerHttpTraceFormat = new JaegerHttpTraceFormat();
@@ -39,7 +40,10 @@ describe('JaegerHttpTraceFormat', () => {
         traceFlags: TraceFlags.SAMPLED,
       };
 
-      jaegerHttpTraceFormat.inject(spanContext, '', carrier);
+      jaegerHttpTraceFormat.inject(
+        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        carrier
+      );
       assert.deepStrictEqual(
         carrier[UBER_TRACE_ID_HEADER],
         'd4cda95b652f4a1592b449d5929fda1b:6e0c63257de34c92:0:01'
@@ -53,7 +57,10 @@ describe('JaegerHttpTraceFormat', () => {
         traceFlags: TraceFlags.SAMPLED,
       };
 
-      customJaegerHttpTraceFormat.inject(spanContext, '', carrier);
+      customJaegerHttpTraceFormat.inject(
+        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        carrier
+      );
       assert.deepStrictEqual(
         carrier[customHeader],
         'd4cda95b652f4a1592b449d5929fda1b:6e0c63257de34c92:0:01'
@@ -65,7 +72,9 @@ describe('JaegerHttpTraceFormat', () => {
     it('should extract context of a sampled span from carrier', () => {
       carrier[UBER_TRACE_ID_HEADER] =
         'd4cda95b652f4a1592b449d5929fda1b:6e0c63257de34c92:0:01';
-      const extractedSpanContext = jaegerHttpTraceFormat.extract('', carrier);
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
+      );
 
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: '6e0c63257de34c92',
@@ -78,7 +87,9 @@ describe('JaegerHttpTraceFormat', () => {
     it('should extract context of a sampled span from carrier with 1 bit flag', () => {
       carrier[UBER_TRACE_ID_HEADER] =
         '9c41e35aeb6d1272:45fd2a9709dadcf1:a13699e3fb724f40:1';
-      const extractedSpanContext = jaegerHttpTraceFormat.extract('', carrier);
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
+      );
 
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: '45fd2a9709dadcf1',
@@ -91,7 +102,9 @@ describe('JaegerHttpTraceFormat', () => {
     it('should extract context of a sampled span from UTF-8 encoded carrier', () => {
       carrier[UBER_TRACE_ID_HEADER] =
         'ac1f3dc3c2c0b06e%3A5ac292c4a11a163e%3Ac086aaa825821068%3A1';
-      const extractedSpanContext = jaegerHttpTraceFormat.extract('', carrier);
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
+      );
 
       assert.deepStrictEqual(extractedSpanContext, {
         spanId: '5ac292c4a11a163e',
@@ -104,9 +117,8 @@ describe('JaegerHttpTraceFormat', () => {
     it('should use custom header if provided', () => {
       carrier[customHeader] =
         'd4cda95b652f4a1592b449d5929fda1b:6e0c63257de34c92:0:01';
-      const extractedSpanContext = customJaegerHttpTraceFormat.extract(
-        '',
-        carrier
+      const extractedSpanContext = Context.getExtractedSpanContext(
+        customJaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
       );
 
       assert.deepStrictEqual(extractedSpanContext, {
@@ -117,15 +129,22 @@ describe('JaegerHttpTraceFormat', () => {
       });
     });
 
-    it('returns null if UBER_TRACE_ID_HEADER header is missing', () => {
-      assert.deepStrictEqual(jaegerHttpTraceFormat.extract('', carrier), null);
+    it('returns undefined if UBER_TRACE_ID_HEADER header is missing', () => {
+      assert.deepStrictEqual(
+        Context.getExtractedSpanContext(
+          jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
+        ),
+        undefined
+      );
     });
 
-    it('returns null if UBER_TRACE_ID_HEADER header is invalid', () => {
+    it('returns undefined if UBER_TRACE_ID_HEADER header is invalid', () => {
       carrier[UBER_TRACE_ID_HEADER] = 'invalid!';
       assert.deepStrictEqual(
-        jaegerHttpTraceFormat.extract('HttpTraceContext', carrier),
-        null
+        Context.getExtractedSpanContext(
+          jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
+        ),
+        undefined
       );
     });
   });
diff --git a/packages/opentelemetry-scope-async-hooks/src/AsyncHooksScopeManager.ts b/packages/opentelemetry-scope-async-hooks/src/AsyncHooksScopeManager.ts
index f3f4ee7f78..b0d1df0c21 100644
--- a/packages/opentelemetry-scope-async-hooks/src/AsyncHooksScopeManager.ts
+++ b/packages/opentelemetry-scope-async-hooks/src/AsyncHooksScopeManager.ts
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { ScopeManager } from '@opentelemetry/scope-base';
+import { ScopeManager, Context } from '@opentelemetry/scope-base';
 import * as asyncHooks from 'async_hooks';
 import { EventEmitter } from 'events';
 
@@ -39,7 +39,9 @@ const ADD_LISTENER_METHODS = [
 
 export class AsyncHooksScopeManager implements ScopeManager {
   private _asyncHook: asyncHooks.AsyncHook;
-  private _scopes: { [uid: number]: unknown } = Object.create(null);
+  private _scopes: {
+    [uid: number]: Context | undefined | null;
+  } = Object.create(null);
 
   constructor() {
     this._asyncHook = asyncHooks.createHook({
@@ -49,12 +51,12 @@ export class AsyncHooksScopeManager implements ScopeManager {
     });
   }
 
-  active(): unknown {
-    return this._scopes[asyncHooks.executionAsyncId()] || undefined;
+  active(): Context {
+    return this._scopes[asyncHooks.executionAsyncId()] || Context.ROOT_CONTEXT;
   }
 
   with<T extends (...args: unknown[]) => ReturnType<T>>(
-    scope: unknown,
+    scope: Context,
     fn: T
   ): ReturnType<T> {
     const uid = asyncHooks.executionAsyncId();
@@ -73,7 +75,7 @@ export class AsyncHooksScopeManager implements ScopeManager {
     }
   }
 
-  bind<T>(target: T, scope?: unknown): T {
+  bind<T>(target: T, scope: Context): T {
     // if no specific scope to propagate is given, we use the current one
     if (scope === undefined) {
       scope = this.active();
@@ -97,7 +99,7 @@ export class AsyncHooksScopeManager implements ScopeManager {
     return this;
   }
 
-  private _bindFunction<T extends Function>(target: T, scope?: unknown): T {
+  private _bindFunction<T extends Function>(target: T, scope: Context): T {
     const manager = this;
     const contextWrapper = function(this: {}, ...args: unknown[]) {
       return manager.with(scope, () => target.apply(this, args));
@@ -125,7 +127,7 @@ export class AsyncHooksScopeManager implements ScopeManager {
    */
   private _bindEventEmitter<T extends EventEmitter>(
     target: T,
-    scope?: unknown
+    scope: Context
   ): T {
     const ee = (target as unknown) as PatchedEventEmitter;
     if (ee.__ot_listeners !== undefined) return target;
@@ -205,7 +207,7 @@ export class AsyncHooksScopeManager implements ScopeManager {
   private _patchAddListener(
     ee: PatchedEventEmitter,
     original: Function,
-    scope?: unknown
+    scope: Context
   ) {
     const scopeManager = this;
     return function(this: {}, event: string, listener: Func<void>) {
diff --git a/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts b/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts
index c5333786f4..6927810b6e 100644
--- a/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts
+++ b/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts
@@ -17,6 +17,7 @@
 import * as assert from 'assert';
 import { AsyncHooksScopeManager } from '../src';
 import { EventEmitter } from 'events';
+import { Context } from '@opentelemetry/scope-base';
 
 describe('AsyncHooksScopeManager', () => {
   let scopeManager: AsyncHooksScopeManager;
@@ -50,11 +51,11 @@ describe('AsyncHooksScopeManager', () => {
 
   describe('.with()', () => {
     it('should run the callback (null as target)', done => {
-      scopeManager.with(null, done);
+      scopeManager.with(Context.ROOT_CONTEXT, done);
     });
 
     it('should run the callback (object as target)', done => {
-      const test = { a: 1 };
+      const test = Context.ROOT_CONTEXT.setValue('a', 1);
       scopeManager.with(test, () => {
         assert.strictEqual(scopeManager.active(), test, 'should have scope');
         return done();
@@ -63,7 +64,7 @@ describe('AsyncHooksScopeManager', () => {
 
     it('should run the callback (when disabled)', done => {
       scopeManager.disable();
-      scopeManager.with(null, () => {
+      scopeManager.with(Context.ROOT_CONTEXT, () => {
         scopeManager.enable();
         return done();
       });
@@ -71,7 +72,7 @@ describe('AsyncHooksScopeManager', () => {
 
     it('should rethrow errors', done => {
       assert.throws(() => {
-        scopeManager.with(null, () => {
+        scopeManager.with(Context.ROOT_CONTEXT, () => {
           throw new Error('This should be rethrown');
         });
       });
@@ -79,14 +80,14 @@ describe('AsyncHooksScopeManager', () => {
     });
 
     it('should finally restore an old scope', done => {
-      const scope1 = 'scope1';
-      const scope2 = 'scope2';
+      const scope1 = Context.ROOT_CONTEXT.setValue('name', 'scope1');
+      const scope2 = Context.ROOT_CONTEXT.setValue('name', 'scope2');
       scopeManager.with(scope1, () => {
-        assert.strictEqual(scopeManager.active(), 'scope1');
+        assert.strictEqual(scopeManager.active(), scope1);
         scopeManager.with(scope2, () => {
-          assert.strictEqual(scopeManager.active(), 'scope2');
+          assert.strictEqual(scopeManager.active(), scope2);
         });
-        assert.strictEqual(scopeManager.active(), 'scope1');
+        assert.strictEqual(scopeManager.active(), scope1);
         return done();
       });
     });
@@ -95,18 +96,24 @@ describe('AsyncHooksScopeManager', () => {
   describe('.bind(function)', () => {
     it('should return the same target (when enabled)', () => {
       const test = { a: 1 };
-      assert.deepStrictEqual(scopeManager.bind(test), test);
+      assert.deepStrictEqual(
+        scopeManager.bind(test, Context.ROOT_CONTEXT),
+        test
+      );
     });
 
     it('should return the same target (when disabled)', () => {
       scopeManager.disable();
       const test = { a: 1 };
-      assert.deepStrictEqual(scopeManager.bind(test), test);
+      assert.deepStrictEqual(
+        scopeManager.bind(test, Context.ROOT_CONTEXT),
+        test
+      );
       scopeManager.enable();
     });
 
     it('should return current scope (when enabled)', done => {
-      const scope = { a: 1 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const fn = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();
@@ -120,7 +127,7 @@ describe('AsyncHooksScopeManager', () => {
      */
     it('should return current scope (when disabled)', done => {
       scopeManager.disable();
-      const scope = { a: 1 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const fn = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();
@@ -130,12 +137,12 @@ describe('AsyncHooksScopeManager', () => {
 
     it('should fail to return current scope (when disabled + async op)', done => {
       scopeManager.disable();
-      const scope = { a: 1 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const fn = scopeManager.bind(() => {
         setTimeout(() => {
           assert.strictEqual(
             scopeManager.active(),
-            undefined,
+            Context.ROOT_CONTEXT,
             'should have no scope'
           );
           return done();
@@ -146,7 +153,7 @@ describe('AsyncHooksScopeManager', () => {
 
     it('should return current scope (when re-enabled + async op)', done => {
       scopeManager.enable();
-      const scope = { a: 1 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const fn = scopeManager.bind(() => {
         setTimeout(() => {
           assert.strictEqual(scopeManager.active(), scope, 'should have scope');
@@ -160,19 +167,19 @@ describe('AsyncHooksScopeManager', () => {
   describe('.bind(event-emitter)', () => {
     it('should return the same target (when enabled)', () => {
       const ee = new EventEmitter();
-      assert.deepStrictEqual(scopeManager.bind(ee), ee);
+      assert.deepStrictEqual(scopeManager.bind(ee, Context.ROOT_CONTEXT), ee);
     });
 
     it('should return the same target (when disabled)', () => {
       const ee = new EventEmitter();
       scopeManager.disable();
-      assert.deepStrictEqual(scopeManager.bind(ee), ee);
+      assert.deepStrictEqual(scopeManager.bind(ee, Context.ROOT_CONTEXT), ee);
       scopeManager.enable();
     });
 
     it('should return current scope and removeListener (when enabled)', done => {
       const ee = new EventEmitter();
-      const scope = { a: 2 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         assert.deepStrictEqual(scopeManager.active(), scope);
@@ -187,7 +194,7 @@ describe('AsyncHooksScopeManager', () => {
 
     it('should return current scope and removeAllListener (when enabled)', done => {
       const ee = new EventEmitter();
-      const scope = { a: 2 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         assert.deepStrictEqual(scopeManager.active(), scope);
@@ -207,7 +214,7 @@ describe('AsyncHooksScopeManager', () => {
     it('should return scope (when disabled)', done => {
       scopeManager.disable();
       const ee = new EventEmitter();
-      const scope = { a: 2 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         assert.deepStrictEqual(scopeManager.active(), scope);
@@ -224,11 +231,11 @@ describe('AsyncHooksScopeManager', () => {
     it('should not return current scope (when disabled + async op)', done => {
       scopeManager.disable();
       const ee = new EventEmitter();
-      const scope = { a: 3 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         setImmediate(() => {
-          assert.deepStrictEqual(scopeManager.active(), undefined);
+          assert.deepStrictEqual(scopeManager.active(), Context.ROOT_CONTEXT);
           patchedEe.removeAllListeners('test');
           assert.strictEqual(patchedEe.listeners('test').length, 0);
           return done();
@@ -242,7 +249,7 @@ describe('AsyncHooksScopeManager', () => {
     it('should return current scope (when enabled + async op)', done => {
       scopeManager.enable();
       const ee = new EventEmitter();
-      const scope = { a: 3 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         setImmediate(() => {
diff --git a/packages/opentelemetry-scope-base/src/NoopScopeManager.ts b/packages/opentelemetry-scope-base/src/NoopScopeManager.ts
index ac32db311f..027f0a2e14 100644
--- a/packages/opentelemetry-scope-base/src/NoopScopeManager.ts
+++ b/packages/opentelemetry-scope-base/src/NoopScopeManager.ts
@@ -15,20 +15,21 @@
  */
 
 import * as types from './types';
+import { Context } from './context';
 
 export class NoopScopeManager implements types.ScopeManager {
-  active(): unknown {
-    return undefined;
+  active(): Context {
+    return Context.ROOT_CONTEXT;
   }
 
   with<T extends (...args: unknown[]) => ReturnType<T>>(
-    scope: unknown,
+    scope: Context,
     fn: T
   ): ReturnType<T> {
     return fn();
   }
 
-  bind<T>(target: T, scope?: unknown): T {
+  bind<T>(target: T, scope?: Context): T {
     return target;
   }
 
diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
new file mode 100644
index 0000000000..6b413e88b2
--- /dev/null
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -0,0 +1,74 @@
+/*!
+ * Copyright 2020, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/** Map of identifiers to an unknown value used internally to store context */
+type Store = { [identifer: string]: unknown };
+
+/**
+ * Class which stores and manages current context values. All methods which
+ * update context such as get and delete do not modify an existing context,
+ * but create a new one with updated values.
+ */
+export class Context {
+  private _context: Store;
+
+  public static readonly ROOT_CONTEXT = new Context();
+
+  /**
+   * Construct a new context which inherits values from an optional parent context.
+   *
+   * @param context a context from which to inherit values
+   */
+  protected constructor(context: Context | Store = {}) {
+    const storage = context instanceof Context ? context._context : context;
+    this._context = Object.assign(Object.create(null), storage);
+  }
+
+  /**
+   * Get a value from the context.
+   *
+   * @param key key which identifies a context value
+   */
+  getValue(key: string): unknown {
+    return this._context[key];
+  }
+
+  /**
+   * Create a new context which inherits from this context and has
+   * the given key set to the given value.
+   *
+   * @param key context key for which to set the value
+   * @param value value to set for the given key
+   */
+  setValue(key: string, value: unknown): Context {
+    return new Context({
+      ...this._context,
+      [key]: value,
+    });
+  }
+
+  /**
+   * Return a new context which inherits from this context but does
+   * not contain a value for the given key.
+   *
+   * @param key context key for which to clear a value
+   */
+  deleteValue(key: string): Context {
+    const context = new Context(this);
+    delete context._context[key];
+    return context;
+  }
+}
diff --git a/packages/opentelemetry-scope-base/src/index.ts b/packages/opentelemetry-scope-base/src/index.ts
index 46f028acc9..3f0c230358 100644
--- a/packages/opentelemetry-scope-base/src/index.ts
+++ b/packages/opentelemetry-scope-base/src/index.ts
@@ -15,4 +15,5 @@
  */
 
 export * from './types';
+export * from './context';
 export * from './NoopScopeManager';
diff --git a/packages/opentelemetry-scope-base/src/types.ts b/packages/opentelemetry-scope-base/src/types.ts
index 4071603c91..9bba83b504 100644
--- a/packages/opentelemetry-scope-base/src/types.ts
+++ b/packages/opentelemetry-scope-base/src/types.ts
@@ -14,11 +14,13 @@
  * limitations under the License.
  */
 
+import { Context } from './context';
+
 export interface ScopeManager {
   /**
    * Get the current active scope
    */
-  active(): unknown;
+  active(): Context;
 
   /**
    * Run the fn callback with object set as the current active scope
@@ -26,7 +28,7 @@ export interface ScopeManager {
    * @param fn A callback to be immediately run within a specific scope
    */
   with<T extends (...args: unknown[]) => ReturnType<T>>(
-    scope: unknown,
+    scope: Context,
     fn: T
   ): ReturnType<T>;
 
@@ -35,7 +37,7 @@ export interface ScopeManager {
    * @param target Any object to which a scope need to be set
    * @param [scope] Optionally specify the scope which you want to assign
    */
-  bind<T>(target: T, scope?: unknown): T;
+  bind<T>(target: T, scope?: Context): T;
 
   /**
    * Enable scope management
diff --git a/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts b/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts
index 4767f5793f..5a9245b666 100644
--- a/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts
+++ b/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts
@@ -15,7 +15,7 @@
  */
 
 import * as assert from 'assert';
-import { NoopScopeManager } from '../src';
+import { NoopScopeManager, Context } from '../src';
 
 describe('NoopScopeManager', () => {
   let scopeManager: NoopScopeManager;
@@ -39,16 +39,16 @@ describe('NoopScopeManager', () => {
   });
 
   describe('.with()', () => {
-    it('should run the callback (null as target)', done => {
-      scopeManager.with(null, done);
+    it('should run the callback (Context.ROOT_CONTEXT as target)', done => {
+      scopeManager.with(Context.ROOT_CONTEXT, done);
     });
 
     it('should run the callback (object as target)', done => {
-      const test = { a: 1 };
+      const test = Context.ROOT_CONTEXT.setValue('a', 1);
       scopeManager.with(test, () => {
         assert.strictEqual(
           scopeManager.active(),
-          undefined,
+          Context.ROOT_CONTEXT,
           'should not have scope'
         );
         return done();
@@ -57,7 +57,7 @@ describe('NoopScopeManager', () => {
 
     it('should run the callback (when disabled)', done => {
       scopeManager.disable();
-      scopeManager.with(null, () => {
+      scopeManager.with(Context.ROOT_CONTEXT, () => {
         scopeManager.enable();
         return done();
       });
@@ -65,19 +65,19 @@ describe('NoopScopeManager', () => {
   });
 
   describe('.active()', () => {
-    it('should always return null (when enabled)', () => {
+    it('should always return Context.ROOT_CONTEXT (when enabled)', () => {
       assert.strictEqual(
         scopeManager.active(),
-        undefined,
+        Context.ROOT_CONTEXT,
         'should not have scope'
       );
     });
 
-    it('should always return null (when disabled)', () => {
+    it('should always return Context.ROOT_CONTEXT (when disabled)', () => {
       scopeManager.disable();
       assert.strictEqual(
         scopeManager.active(),
-        undefined,
+        Context.ROOT_CONTEXT,
         'should not have scope'
       );
       scopeManager.enable();
diff --git a/packages/opentelemetry-scope-zone-peer-dep/src/ZoneScopeManager.ts b/packages/opentelemetry-scope-zone-peer-dep/src/ZoneScopeManager.ts
index d735e73c7d..71b3c6be45 100644
--- a/packages/opentelemetry-scope-zone-peer-dep/src/ZoneScopeManager.ts
+++ b/packages/opentelemetry-scope-zone-peer-dep/src/ZoneScopeManager.ts
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { ScopeManager } from '@opentelemetry/scope-base';
+import { ScopeManager, Context } from '@opentelemetry/scope-base';
 import { Func, TargetWithEvents } from './types';
 import { isListenerObject } from './util';
 
@@ -45,20 +45,20 @@ export class ZoneScopeManager implements ScopeManager {
    * Returns the active scope from certain zone name
    * @param activeZone
    */
-  private _activeScopeFromZone(
-    activeZone: Zone | undefined
-  ): unknown | undefined {
-    return activeZone && activeZone.get(ZONE_SCOPE_KEY);
+  private _activeScopeFromZone(activeZone: Zone | undefined): Context {
+    return (
+      (activeZone && activeZone.get(ZONE_SCOPE_KEY)) || Context.ROOT_CONTEXT
+    );
   }
 
   /**
    * @param target Function to be executed within the scope
    * @param scope A scope (span) to be executed within target function
    */
-  private _bindFunction<T extends Function>(target: T, scope?: unknown): T {
+  private _bindFunction<T extends Function>(target: T, scope: Context): T {
     const manager = this;
     const contextWrapper = function(this: any, ...args: unknown[]) {
-      return manager.with(scope, () => target.apply(this || scope, args));
+      return manager.with(scope, () => target.apply(this, args));
     };
     Object.defineProperty(contextWrapper, 'length', {
       enumerable: false,
@@ -73,7 +73,7 @@ export class ZoneScopeManager implements ScopeManager {
    * @param obj target object on which the listeners will be patched
    * @param scope A scope (span) to be bind to target
    */
-  private _bindListener<T>(obj: T, scope?: unknown): T {
+  private _bindListener<T>(obj: T, scope: Context): T {
     const target = (obj as unknown) as TargetWithEvents;
     if (target.__ot_listeners !== undefined) {
       return obj;
@@ -137,7 +137,7 @@ export class ZoneScopeManager implements ScopeManager {
   private _patchAddEventListener(
     target: TargetWithEvents,
     original: Function,
-    scope?: unknown
+    scope: Context
   ) {
     const scopeManager = this;
 
@@ -183,17 +183,18 @@ export class ZoneScopeManager implements ScopeManager {
   /**
    * Returns the active scope
    */
-  active(): unknown | undefined {
+  active(): Context {
+    if (!this._enabled) {
+      return Context.ROOT_CONTEXT;
+    }
     const activeZone = this._getActiveZone();
 
     const active = this._activeScopeFromZone(activeZone);
     if (active) {
       return active;
     }
-    if (this._enabled) {
-      return window;
-    }
-    return undefined;
+
+    return Context.ROOT_CONTEXT;
   }
 
   /**
@@ -201,7 +202,7 @@ export class ZoneScopeManager implements ScopeManager {
    * @param target
    * @param scope A scope (span) to be bind to target
    */
-  bind<T>(target: T | TargetWithEvents, scope?: unknown): T {
+  bind<T>(target: T | TargetWithEvents, scope: Context): T {
     // if no specific scope to propagate is given, we use the current one
     if (scope === undefined) {
       scope = this.active();
@@ -226,9 +227,6 @@ export class ZoneScopeManager implements ScopeManager {
    * Enables the scope manager and creates a default(root) scope
    */
   enable(): this {
-    if (this._enabled) {
-      return this;
-    }
     this._enabled = true;
     return this;
   }
@@ -241,14 +239,9 @@ export class ZoneScopeManager implements ScopeManager {
    * @param fn Callback function
    */
   with<T extends (...args: unknown[]) => ReturnType<T>>(
-    scope: unknown,
+    scope: Context | null,
     fn: () => ReturnType<T>
   ): ReturnType<T> {
-    // if no scope use active from active zone
-    if (typeof scope === 'undefined' || scope === null) {
-      scope = this.active();
-    }
-
     const zoneName = this._createZoneName();
 
     const newZone = this._createZone(zoneName, scope);
diff --git a/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts b/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
index 490d5bfe45..8973c7e06e 100644
--- a/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
+++ b/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
@@ -18,6 +18,7 @@ import 'zone.js';
 import * as sinon from 'sinon';
 import * as assert from 'assert';
 import { ZoneScopeManager } from '../src';
+import { Context } from '@opentelemetry/scope-base';
 
 let clock: any;
 
@@ -37,18 +38,27 @@ describe('ZoneScopeManager', () => {
 
   describe('.enable()', () => {
     it('should work', () => {
+      const ctx = Context.ROOT_CONTEXT.setValue('a', 1);
       assert.doesNotThrow(() => {
         assert(scopeManager.enable() === scopeManager, 'should return this');
-        assert(scopeManager.active() === window, 'should has root scope');
+        scopeManager.with(ctx, () => {
+          assert(scopeManager.active() === ctx, 'should has root scope');
+        });
       });
     });
   });
 
   describe('.disable()', () => {
     it('should work', () => {
+      const ctx = Context.ROOT_CONTEXT.setValue('a', 1);
       assert.doesNotThrow(() => {
         assert(scopeManager.disable() === scopeManager, 'should return this');
-        assert(scopeManager.active() === undefined, 'should has no scope');
+        scopeManager.with(ctx, () => {
+          assert(
+            scopeManager.active() === Context.ROOT_CONTEXT,
+            'should has root scope'
+          );
+        });
       });
     });
   });
@@ -59,7 +69,7 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should run the callback (object as target)', done => {
-      const test = { a: 1 };
+      const test = Context.ROOT_CONTEXT.setValue('a', 1);
       scopeManager.with(test, () => {
         assert.strictEqual(scopeManager.active(), test, 'should have scope');
         return done();
@@ -84,22 +94,22 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should finally restore an old scope, including the async task', done => {
-      const scope1 = 'scope1';
-      const scope2 = 'scope2';
-      const scope3 = 'scope3';
+      const scope1 = Context.ROOT_CONTEXT.setValue('scope', 'scope1');
+      const scope2 = Context.ROOT_CONTEXT.setValue('scope', 'scope2');
+      const scope3 = Context.ROOT_CONTEXT.setValue('scope', 'scope3');
 
       scopeManager.with(scope1, () => {
-        assert.strictEqual(scopeManager.active(), 'scope1');
+        assert.strictEqual(scopeManager.active(), scope1);
         scopeManager.with(scope2, () => {
-          assert.strictEqual(scopeManager.active(), 'scope2');
+          assert.strictEqual(scopeManager.active(), scope2);
           scopeManager.with(scope3, () => {
-            assert.strictEqual(scopeManager.active(), 'scope3');
+            assert.strictEqual(scopeManager.active(), scope3);
           });
-          assert.strictEqual(scopeManager.active(), 'scope2');
+          assert.strictEqual(scopeManager.active(), scope2);
         });
-        assert.strictEqual(scopeManager.active(), 'scope1');
+        assert.strictEqual(scopeManager.active(), scope1);
         setTimeout(() => {
-          assert.strictEqual(scopeManager.active(), 'scope1');
+          assert.strictEqual(scopeManager.active(), scope1);
           done();
         }, 500);
         clock.tick(500);
@@ -108,9 +118,9 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should finally restore an old scope when scope is an object, including the async task', done => {
-      const scope1 = { a: 1 };
-      const scope2 = { a: 2 };
-      const scope3 = { a: 3 };
+      const scope1 = Context.ROOT_CONTEXT.setValue('x', 1);
+      const scope2 = Context.ROOT_CONTEXT.setValue('x', 2);
+      const scope3 = Context.ROOT_CONTEXT.setValue('x', 3);
       scopeManager.with(scope1, () => {
         assert.strictEqual(scopeManager.active(), scope1);
         scopeManager.with(scope2, () => {
@@ -130,20 +140,29 @@ describe('ZoneScopeManager', () => {
       assert.strictEqual(scopeManager.active(), window);
     });
     it('should correctly return the scopes for 3 parallel actions', () => {
-      const rootSpan = { name: 'rootSpan' };
+      const rootSpan = Context.ROOT_CONTEXT.setValue('name', 'root');
       scopeManager.with(rootSpan, () => {
         assert.ok(
-          scopeManager.active() === rootSpan,
+          scopeManager.active().getValue('name') === 'root',
           'Current span is rootSpan'
         );
-        const concurrentSpan1 = { name: 'concurrentSpan1' };
-        const concurrentSpan2 = { name: 'concurrentSpan2' };
-        const concurrentSpan3 = { name: 'concurrentSpan3' };
+        const concurrentSpan1 = Context.ROOT_CONTEXT.setValue(
+          'span',
+          'concurrentSpan1'
+        );
+        const concurrentSpan2 = Context.ROOT_CONTEXT.setValue(
+          'span',
+          'concurrentSpan2'
+        );
+        const concurrentSpan3 = Context.ROOT_CONTEXT.setValue(
+          'span',
+          'concurrentSpan3'
+        );
 
         scopeManager.with(concurrentSpan1, () => {
           setTimeout(() => {
             assert.ok(
-              scopeManager.active() === concurrentSpan1,
+              scopeManager.active().getValue('span') === concurrentSpan1,
               'Current span is concurrentSpan1'
             );
           }, 10);
@@ -152,7 +171,7 @@ describe('ZoneScopeManager', () => {
         scopeManager.with(concurrentSpan2, () => {
           setTimeout(() => {
             assert.ok(
-              scopeManager.active() === concurrentSpan2,
+              scopeManager.active().getValue('span') === concurrentSpan2,
               'Current span is concurrentSpan2'
             );
           }, 20);
@@ -161,7 +180,7 @@ describe('ZoneScopeManager', () => {
         scopeManager.with(concurrentSpan3, () => {
           setTimeout(() => {
             assert.ok(
-              scopeManager.active() === concurrentSpan3,
+              scopeManager.active().getValue('span') === concurrentSpan3,
               'Current span is concurrentSpan3'
             );
           }, 30);
@@ -180,31 +199,38 @@ describe('ZoneScopeManager', () => {
         }
 
         getTitle() {
-          return this.title;
+          return (scopeManager.active().getValue('obj') as Obj).title;
         }
       }
 
       const obj1 = new Obj('a1');
+      const ctx = Context.ROOT_CONTEXT.setValue('obj', obj1);
       obj1.title = 'a2';
       const obj2 = new Obj('b1');
-      const wrapper: any = scopeManager.bind(obj2.getTitle, obj1);
+      const wrapper: any = scopeManager.bind(obj2.getTitle, ctx);
       assert.ok(wrapper(), 'a2');
     });
 
     it('should return the same target (when enabled)', () => {
       const test = { a: 1 };
-      assert.deepStrictEqual(scopeManager.bind(test), test);
+      assert.deepStrictEqual(
+        scopeManager.bind(test, Context.ROOT_CONTEXT),
+        test
+      );
     });
 
     it('should return the same target (when disabled)', () => {
       scopeManager.disable();
       const test = { a: 1 };
-      assert.deepStrictEqual(scopeManager.bind(test), test);
+      assert.deepStrictEqual(
+        scopeManager.bind(test, Context.ROOT_CONTEXT),
+        test
+      );
       scopeManager.enable();
     });
 
     it('should return current scope (when enabled)', done => {
-      const scope = { a: 1 };
+      const scope = Context.ROOT_CONTEXT.setValue('ctx', { a: 1 });
       const fn: any = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();
@@ -212,18 +238,22 @@ describe('ZoneScopeManager', () => {
       fn();
     });
 
-    it('should return current scope (when disabled)', done => {
+    it('should return root scope (when disabled)', done => {
       scopeManager.disable();
-      const scope = { a: 1 };
+      const scope = Context.ROOT_CONTEXT.setValue('ctx', { a: 1 });
       const fn: any = scopeManager.bind(() => {
-        assert.strictEqual(scopeManager.active(), scope, 'should have scope');
+        assert.strictEqual(
+          scopeManager.active(),
+          Context.ROOT_CONTEXT,
+          'should have scope'
+        );
         return done();
       }, scope);
       fn();
     });
 
     it('should bind the the certain scope to the target "addEventListener" function', done => {
-      const scope1 = { a: 1 };
+      const scope1 = Context.ROOT_CONTEXT.setValue('a', 1);
       const element = document.createElement('div');
 
       scopeManager.bind(element, scope1);
@@ -247,7 +277,7 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should preserve zone when creating new click event inside zone', done => {
-      const scope1 = { a: 1 };
+      const scope1 = Context.ROOT_CONTEXT.setValue('a', 1);
       const element = document.createElement('div');
 
       scopeManager.bind(element, scope1);
diff --git a/packages/opentelemetry-shim-opentracing/src/shim.ts b/packages/opentelemetry-shim-opentracing/src/shim.ts
index 778f440c57..7fdf9b1044 100644
--- a/packages/opentelemetry-shim-opentracing/src/shim.ts
+++ b/packages/opentelemetry-shim-opentracing/src/shim.ts
@@ -15,7 +15,8 @@
  */
 
 import * as types from '@opentelemetry/api';
-import { NoopLogger } from '@opentelemetry/core';
+import { Carrier } from '@opentelemetry/api';
+import { Context, NoopLogger } from '@opentelemetry/core';
 import * as opentracing from 'opentracing';
 
 function translateReferences(
@@ -120,16 +121,23 @@ export class TracerShim extends opentracing.Tracer {
   _inject(
     spanContext: opentracing.SpanContext,
     format: string,
-    carrier: unknown
+    carrier: Carrier
   ): void {
     const opentelemSpanContext: types.SpanContext = (spanContext as SpanContextShim).getSpanContext();
+    if (!carrier || typeof carrier !== 'object') return;
     switch (format) {
       // tslint:disable-next-line:no-switch-case-fall-through
       case opentracing.FORMAT_HTTP_HEADERS:
       case opentracing.FORMAT_TEXT_MAP:
         this._tracer
           .getHttpTextFormat()
-          .inject(opentelemSpanContext, format, carrier);
+          .inject(
+            Context.setExtractedSpanContext(
+              Context.ROOT_CONTEXT,
+              opentelemSpanContext
+            ),
+            carrier
+          );
         return;
       case opentracing.FORMAT_BINARY:
         this._logger.warn(
@@ -141,14 +149,16 @@ export class TracerShim extends opentracing.Tracer {
     }
   }
 
-  _extract(format: string, carrier: unknown): opentracing.SpanContext | null {
+  _extract(format: string, carrier: Carrier): opentracing.SpanContext | null {
     switch (format) {
       // tslint:disable-next-line:no-switch-case-fall-through
       case opentracing.FORMAT_HTTP_HEADERS:
       case opentracing.FORMAT_TEXT_MAP:
-        const context = this._tracer
-          .getHttpTextFormat()
-          .extract(format, carrier);
+        const context = Context.getExtractedSpanContext(
+          this._tracer
+            .getHttpTextFormat()
+            .extract(Context.ROOT_CONTEXT, carrier)
+        );
         if (!context) {
           return null;
         }
diff --git a/packages/opentelemetry-tracing/src/Tracer.ts b/packages/opentelemetry-tracing/src/Tracer.ts
index baf4a375b3..3cccbfce04 100644
--- a/packages/opentelemetry-tracing/src/Tracer.ts
+++ b/packages/opentelemetry-tracing/src/Tracer.ts
@@ -21,6 +21,7 @@ import {
   randomSpanId,
   NoRecordingSpan,
   ConsoleLogger,
+  Context,
 } from '@opentelemetry/core';
 import { TracerConfig, TraceParams } from './types';
 import { ScopeManager } from '@opentelemetry/scope-base';
@@ -106,16 +107,11 @@ export class Tracer implements types.Tracer {
   /**
    * Returns the current Span from the current context.
    *
-   * If there is no Span associated with the current context, null is returned.
+   * If there is no Span associated with the current context, undefined is returned.
    */
   getCurrentSpan(): types.Span | undefined {
     // Get the current Span from the context or null if none found.
-    const current = this._scopeManager.active();
-    if (current === null || current === undefined) {
-      return;
-    } else {
-      return current as types.Span;
-    }
+    return Context.getActiveSpan(this._scopeManager.active());
   }
 
   /**
@@ -126,14 +122,22 @@ export class Tracer implements types.Tracer {
     fn: T
   ): ReturnType<T> {
     // Set given span to context.
-    return this._scopeManager.with(span, fn);
+    return this._scopeManager.with(
+      Context.setActiveSpan(this._scopeManager.active(), span),
+      fn
+    );
   }
 
   /**
    * Bind a span (or the current one) to the target's scope
    */
   bind<T>(target: T, span?: types.Span): T {
-    return this._scopeManager.bind(target, span);
+    return this._scopeManager.bind(
+      target,
+      span
+        ? Context.setActiveSpan(this._scopeManager.active(), span)
+        : this._scopeManager.active()
+    );
   }
 
   /**
diff --git a/packages/opentelemetry-tracing/test/BasicTracerRegistry.test.ts b/packages/opentelemetry-tracing/test/BasicTracerRegistry.test.ts
index ad29673636..7f8e8047ce 100644
--- a/packages/opentelemetry-tracing/test/BasicTracerRegistry.test.ts
+++ b/packages/opentelemetry-tracing/test/BasicTracerRegistry.test.ts
@@ -14,9 +14,11 @@
  * limitations under the License.
  */
 
+import { TraceFlags } from '@opentelemetry/api';
 import {
   ALWAYS_SAMPLER,
   BinaryTraceContext,
+  Context,
   HttpTraceContext,
   NEVER_SAMPLER,
   NoopLogger,
@@ -24,7 +26,6 @@ import {
   TraceState,
 } from '@opentelemetry/core';
 import { NoopScopeManager, ScopeManager } from '@opentelemetry/scope-base';
-import { TraceFlags } from '@opentelemetry/api';
 import * as assert from 'assert';
 import { BasicTracerProvider, Span } from '../src';
 
@@ -315,7 +316,8 @@ describe('BasicTracerProvider', () => {
     it('should return current span when it exists', () => {
       const tracer = new BasicTracerProvider({
         scopeManager: {
-          active: () => 'foo',
+          active: () =>
+            Context.setActiveSpan(Context.ROOT_CONTEXT, ('foo' as any) as Span),
         } as ScopeManager,
       }).getTracer('default');
       assert.deepStrictEqual(tracer.getCurrentSpan(), 'foo');
diff --git a/packages/opentelemetry-web/src/StackScopeManager.ts b/packages/opentelemetry-web/src/StackScopeManager.ts
index c6dc866c20..5fe39459e8 100644
--- a/packages/opentelemetry-web/src/StackScopeManager.ts
+++ b/packages/opentelemetry-web/src/StackScopeManager.ts
@@ -15,6 +15,7 @@
  */
 
 import { ScopeManager } from '@opentelemetry/scope-base';
+import { Context } from '@opentelemetry/core';
 
 /**
  * Stack Scope Manager for managing the state in web
@@ -29,14 +30,17 @@ export class StackScopeManager implements ScopeManager {
   /**
    * Keeps the reference to current scope
    */
-  public _currentScope: unknown;
+  public _currentScope = Context.ROOT_CONTEXT;
 
   /**
    *
    * @param target Function to be executed within the scope
    * @param scope
    */
-  private _bindFunction<T extends Function>(target: T, scope?: unknown): T {
+  private _bindFunction<T extends Function>(
+    target: T,
+    scope = Context.ROOT_CONTEXT
+  ): T {
     const manager = this;
     const contextWrapper = function(...args: unknown[]) {
       return manager.with(scope, () => target.apply(scope, args));
@@ -53,7 +57,7 @@ export class StackScopeManager implements ScopeManager {
   /**
    * Returns the active scope
    */
-  active(): unknown {
+  active(): Context {
     return this._currentScope;
   }
 
@@ -62,7 +66,7 @@ export class StackScopeManager implements ScopeManager {
    * @param target
    * @param scope
    */
-  bind<T>(target: T, scope?: unknown): T {
+  bind<T>(target: T, scope = Context.ROOT_CONTEXT): T {
     // if no specific scope to propagate is given, we use the current one
     if (scope === undefined) {
       scope = this.active();
@@ -77,7 +81,7 @@ export class StackScopeManager implements ScopeManager {
    * Disable the scope manager (clears the current scope)
    */
   disable(): this {
-    this._currentScope = undefined;
+    this._currentScope = Context.ROOT_CONTEXT;
     this._enabled = false;
     return this;
   }
@@ -90,7 +94,7 @@ export class StackScopeManager implements ScopeManager {
       return this;
     }
     this._enabled = true;
-    this._currentScope = window;
+    this._currentScope = Context.ROOT_CONTEXT;
     return this;
   }
 
@@ -101,15 +105,11 @@ export class StackScopeManager implements ScopeManager {
    * @param fn Callback function
    */
   with<T extends (...args: unknown[]) => ReturnType<T>>(
-    scope: unknown,
+    scope: Context | null,
     fn: () => ReturnType<T>
   ): ReturnType<T> {
-    if (typeof scope === 'undefined' || scope === null) {
-      scope = window;
-    }
-
     const previousScope = this._currentScope;
-    this._currentScope = scope;
+    this._currentScope = scope || Context.ROOT_CONTEXT;
 
     try {
       return fn.apply(scope);
diff --git a/packages/opentelemetry-web/test/StackScopeManager.test.ts b/packages/opentelemetry-web/test/StackScopeManager.test.ts
index 781dfa87f3..680334a591 100644
--- a/packages/opentelemetry-web/test/StackScopeManager.test.ts
+++ b/packages/opentelemetry-web/test/StackScopeManager.test.ts
@@ -16,6 +16,7 @@
 
 import * as assert from 'assert';
 import { StackScopeManager } from '../src';
+import { Context } from '@opentelemetry/core';
 
 describe('StackScopeManager', () => {
   let scopeManager: StackScopeManager;
@@ -33,7 +34,10 @@ describe('StackScopeManager', () => {
     it('should work', () => {
       assert.doesNotThrow(() => {
         assert(scopeManager.enable() === scopeManager, 'should return this');
-        assert(scopeManager.active() === window, 'should has root scope');
+        assert(
+          scopeManager.active() === Context.ROOT_CONTEXT,
+          'should has root scope'
+        );
       });
     });
   });
@@ -42,7 +46,10 @@ describe('StackScopeManager', () => {
     it('should work', () => {
       assert.doesNotThrow(() => {
         assert(scopeManager.disable() === scopeManager, 'should return this');
-        assert(scopeManager.active() === undefined, 'should has no scope');
+        assert(
+          scopeManager.active() === Context.ROOT_CONTEXT,
+          'should has no scope'
+        );
       });
     });
   });
@@ -53,7 +60,7 @@ describe('StackScopeManager', () => {
     });
 
     it('should run the callback (object as target)', done => {
-      const test = { a: 1 };
+      const test = Context.ROOT_CONTEXT.setValue('a', 1);
       scopeManager.with(test, () => {
         assert.strictEqual(scopeManager.active(), test, 'should have scope');
         return done();
@@ -78,28 +85,28 @@ describe('StackScopeManager', () => {
     });
 
     it('should finally restore an old scope', done => {
-      const scope1 = 'scope1';
-      const scope2 = 'scope2';
-      const scope3 = 'scope3';
+      const scope1 = Context.ROOT_CONTEXT.setValue('name', 'scope1');
+      const scope2 = Context.ROOT_CONTEXT.setValue('name', 'scope2');
+      const scope3 = Context.ROOT_CONTEXT.setValue('name', 'scope3');
       scopeManager.with(scope1, () => {
-        assert.strictEqual(scopeManager.active(), 'scope1');
+        assert.strictEqual(scopeManager.active(), scope1);
         scopeManager.with(scope2, () => {
-          assert.strictEqual(scopeManager.active(), 'scope2');
+          assert.strictEqual(scopeManager.active(), scope2);
           scopeManager.with(scope3, () => {
-            assert.strictEqual(scopeManager.active(), 'scope3');
+            assert.strictEqual(scopeManager.active(), scope3);
           });
-          assert.strictEqual(scopeManager.active(), 'scope2');
+          assert.strictEqual(scopeManager.active(), scope2);
         });
-        assert.strictEqual(scopeManager.active(), 'scope1');
+        assert.strictEqual(scopeManager.active(), scope1);
         return done();
       });
       assert.strictEqual(scopeManager.active(), window);
     });
 
     it('should finally restore an old scope when scope is an object', done => {
-      const scope1 = { a: 1 };
-      const scope2 = { a: 2 };
-      const scope3 = { a: 3 };
+      const scope1 = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope2 = Context.ROOT_CONTEXT.setValue('a', 2);
+      const scope3 = Context.ROOT_CONTEXT.setValue('a', 3);
       scopeManager.with(scope1, () => {
         assert.strictEqual(scopeManager.active(), scope1);
         scopeManager.with(scope2, () => {
@@ -126,31 +133,32 @@ describe('StackScopeManager', () => {
         }
 
         getTitle() {
-          return this.title;
+          return (scopeManager.active().getValue('obj') as Obj).title;
         }
       }
 
       const obj1 = new Obj('a1');
+      const ctx = Context.ROOT_CONTEXT.setValue('obj', obj1);
       obj1.title = 'a2';
       const obj2 = new Obj('b1');
-      const wrapper: any = scopeManager.bind(obj2.getTitle, obj1);
+      const wrapper: any = scopeManager.bind(obj2.getTitle, ctx);
       assert.ok(wrapper(), 'a2');
     });
 
     it('should return the same target (when enabled)', () => {
-      const test = { a: 1 };
+      const test = Context.ROOT_CONTEXT.setValue('a', 1);
       assert.deepStrictEqual(scopeManager.bind(test), test);
     });
 
     it('should return the same target (when disabled)', () => {
       scopeManager.disable();
-      const test = { a: 1 };
+      const test = Context.ROOT_CONTEXT.setValue('a', 1);
       assert.deepStrictEqual(scopeManager.bind(test), test);
       scopeManager.enable();
     });
 
     it('should return current scope (when enabled)', done => {
-      const scope = { a: 1 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const fn: any = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();
@@ -160,7 +168,7 @@ describe('StackScopeManager', () => {
 
     it('should return current scope (when disabled)', done => {
       scopeManager.disable();
-      const scope = { a: 1 };
+      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
       const fn: any = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();

From 5a03016af52dd849aaf956e355c76cfe04287fb5 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 10:30:19 -0500
Subject: [PATCH 02/23] chore: fix api dependencies on builds

---
 .circleci/config.yml | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 800faeed2d..264a16d65a 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -165,6 +165,9 @@ jobs:
       - run:
           name: Install minimal doc and lint modules globally
           command: npm i -g tslint lerna typedoc linkinator typescript gts tslint-consistent-codestyle tslint-microsoft-contrib
+      - run:
+          name: Install API dependencies
+          command: lerna bootstrap --scope @opentelemetry/api --include-filtered-dependencies
       - run:
           name: Symlink global modules into all lerna packages
           command: lerna exec 'npm link tslint lerna typedoc linkinator typescript gts tslint-consistent-codestyle tslint-microsoft-contrib'

From 04fb334828709da3ed27066e6563f3e1ddf99d09 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 10:38:49 -0500
Subject: [PATCH 03/23] chore: use bootstrap for doc deps

---
 .circleci/config.yml | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 264a16d65a..39b402a342 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -164,13 +164,10 @@ jobs:
       - checkout
       - run:
           name: Install minimal doc and lint modules globally
-          command: npm i -g tslint lerna typedoc linkinator typescript gts tslint-consistent-codestyle tslint-microsoft-contrib
+          command: npm i -g lerna
       - run:
           name: Install API dependencies
           command: lerna bootstrap --scope @opentelemetry/api --include-filtered-dependencies
-      - run:
-          name: Symlink global modules into all lerna packages
-          command: lerna exec 'npm link tslint lerna typedoc linkinator typescript gts tslint-consistent-codestyle tslint-microsoft-contrib'
       - run:
           name: Check code style and linting
           command: npm run check

From 33912072f6dd99ba14f6bc35ddbdaef602515fdc Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 10:54:47 -0500
Subject: [PATCH 04/23] chore: allow builds as root in docs

---
 .circleci/config.yml | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 39b402a342..2ef49b3c10 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -160,6 +160,8 @@ jobs:
   lint_&_docs:
     docker:
       - image: node:12
+        environment:
+          NPM_CONFIG_UNSAFE_PERM: true
     steps:
       - checkout
       - run:
@@ -167,7 +169,7 @@ jobs:
           command: npm i -g lerna
       - run:
           name: Install API dependencies
-          command: lerna bootstrap --scope @opentelemetry/api --include-filtered-dependencies
+          command: lerna bootstrap --no-ci -- --only=dev
       - run:
           name: Check code style and linting
           command: npm run check

From 8467706bf2a43bc1d703216357937904c21db9b6 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 11:05:06 -0500
Subject: [PATCH 05/23] chore: bootstrap docs after checking code

---
 .circleci/config.yml | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 2ef49b3c10..140a524a71 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -160,19 +160,20 @@ jobs:
   lint_&_docs:
     docker:
       - image: node:12
-        environment:
-          NPM_CONFIG_UNSAFE_PERM: true
     steps:
       - checkout
       - run:
           name: Install minimal doc and lint modules globally
-          command: npm i -g lerna
+          command: npm i -g tslint lerna typedoc linkinator typescript gts tslint-consistent-codestyle tslint-microsoft-contrib
       - run:
-          name: Install API dependencies
-          command: lerna bootstrap --no-ci -- --only=dev
+          name: Symlink global modules into all lerna packages
+          command: lerna exec 'npm link tslint lerna typedoc linkinator typescript gts tslint-consistent-codestyle tslint-microsoft-contrib'
       - run:
           name: Check code style and linting
           command: npm run check
+      - run:
+          name: Install API dependencies
+          command: lerna bootstrap --scope @opentelemetry/api --include-filtered-dependencies
       - run:
           name: Docs tests
           command: npm run docs-test

From 707655328738b2a6578792721ca2a1ed2dde5e46 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 11:08:27 -0500
Subject: [PATCH 06/23] chore: allow unsafe builds in docs

---
 .circleci/config.yml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 140a524a71..e04d9f22ba 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -160,6 +160,8 @@ jobs:
   lint_&_docs:
     docker:
       - image: node:12
+        environment:
+          NPM_CONFIG_UNSAFE_PERM: true
     steps:
       - checkout
       - run:

From 13180003dcb88cd2c923f454b8a295bbb0cf9802 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 12:03:09 -0500
Subject: [PATCH 07/23] chore: fix api test build

---
 .../test/noop-implementations/noop-meter.test.ts               | 2 --
 packages/opentelemetry-api/tsconfig.json                       | 3 ++-
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts b/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts
index 052854e82b..bbbd0643b3 100644
--- a/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts
+++ b/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts
@@ -50,10 +50,8 @@ describe('NoopMeter', () => {
 
     const measure = meter.createMeasure('some-name');
     measure.getDefaultBound().record(1);
-    measure.getDefaultBound().record(1, { key: { value: 'value' } });
     measure.getDefaultBound().record(
       1,
-      { key: { value: 'value' } },
       {
         traceId: 'a3cda95b652f4a1592b449d5929fda1b',
         spanId: '5e0c63257de34c92',
diff --git a/packages/opentelemetry-api/tsconfig.json b/packages/opentelemetry-api/tsconfig.json
index 2b05ed8413..df95d9cc57 100644
--- a/packages/opentelemetry-api/tsconfig.json
+++ b/packages/opentelemetry-api/tsconfig.json
@@ -5,7 +5,8 @@
     "outDir": "build"
   },
   "include": [
-    "src/**/*.ts"
+    "src/**/*.ts",
+    "test/**/*.ts"
   ],
   "typedocOptions": {
     "name": "OpenTelemetry API for JavaScript",

From 55338813d9569932ffa0c818e2b8ceb1a6689744 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 12:06:40 -0500
Subject: [PATCH 08/23] chore: lint

---
 .../opentelemetry-api/test/api/api.test.ts    | 20 +++++++++++--------
 .../noop-implementations/noop-meter.test.ts   | 14 +++++--------
 .../noop-implementations/noop-span.test.ts    |  8 +++++++-
 .../noop-implementations/noop-tracer.test.ts  |  5 ++++-
 4 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/packages/opentelemetry-api/test/api/api.test.ts b/packages/opentelemetry-api/test/api/api.test.ts
index c0ecb9baf9..031fa6f976 100644
--- a/packages/opentelemetry-api/test/api/api.test.ts
+++ b/packages/opentelemetry-api/test/api/api.test.ts
@@ -15,7 +15,14 @@
  */
 
 import * as assert from 'assert';
-import api, { TraceFlags, NoopSpan, NoopTracerProvider, NoopTracer, SpanOptions, Span } from '../../src';
+import api, {
+  TraceFlags,
+  NoopSpan,
+  NoopTracerProvider,
+  NoopTracer,
+  SpanOptions,
+  Span,
+} from '../../src';
 
 describe('API', () => {
   const functions = [
@@ -27,7 +34,7 @@ describe('API', () => {
   ];
 
   it('should expose a tracer provider via getTracerProvider', () => {
-    const tracer =  api.trace.getTracerProvider();
+    const tracer = api.trace.getTracerProvider();
     assert.ok(tracer);
     assert.strictEqual(typeof tracer, 'object');
   });
@@ -46,7 +53,7 @@ describe('API', () => {
 
     it('should not crash', () => {
       functions.forEach(fn => {
-        const tracer =  api.trace.getTracerProvider();
+        const tracer = api.trace.getTracerProvider();
         try {
           ((tracer as unknown) as { [fn: string]: Function })[fn](); // Try to run the function
           assert.ok(true, fn);
@@ -60,16 +67,13 @@ describe('API', () => {
 
     it('should use the global tracer provider', () => {
       api.trace.initGlobalTracerProvider(new TestTracerProvider());
-      const tracer =  api.trace.getTracerProvider().getTracer('name');
+      const tracer = api.trace.getTracerProvider().getTracer('name');
       const span = tracer.startSpan('test');
       assert.deepStrictEqual(span, dummySpan);
     });
 
     class TestTracer extends NoopTracer {
-      startSpan(
-        name: string,
-        options?: SpanOptions | undefined
-      ): Span {
+      startSpan(name: string, options?: SpanOptions | undefined): Span {
         return dummySpan;
       }
     }
diff --git a/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts b/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts
index bbbd0643b3..21cb6171f0 100644
--- a/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts
+++ b/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts
@@ -23,10 +23,9 @@ import {
   NOOP_BOUND_MEASURE,
   NOOP_COUNTER_METRIC,
   NOOP_GAUGE_METRIC,
-  NOOP_MEASURE_METRIC
+  NOOP_MEASURE_METRIC,
 } from '../../src';
 
-
 describe('NoopMeter', () => {
   it('should not crash', () => {
     const meter = new NoopMeterProvider().getMeter('test-noop');
@@ -50,13 +49,10 @@ describe('NoopMeter', () => {
 
     const measure = meter.createMeasure('some-name');
     measure.getDefaultBound().record(1);
-    measure.getDefaultBound().record(
-      1,
-      {
-        traceId: 'a3cda95b652f4a1592b449d5929fda1b',
-        spanId: '5e0c63257de34c92',
-      }
-    );
+    measure.getDefaultBound().record(1, {
+      traceId: 'a3cda95b652f4a1592b449d5929fda1b',
+      spanId: '5e0c63257de34c92',
+    });
 
     // ensure the correct noop const is returned
     assert.strictEqual(measure, NOOP_MEASURE_METRIC);
diff --git a/packages/opentelemetry-api/test/noop-implementations/noop-span.test.ts b/packages/opentelemetry-api/test/noop-implementations/noop-span.test.ts
index 0350a9ab53..a42d471189 100644
--- a/packages/opentelemetry-api/test/noop-implementations/noop-span.test.ts
+++ b/packages/opentelemetry-api/test/noop-implementations/noop-span.test.ts
@@ -15,7 +15,13 @@
  */
 
 import * as assert from 'assert';
-import { CanonicalCode, INVALID_SPAN_ID, INVALID_TRACE_ID, NoopSpan, TraceFlags } from '../../src';
+import {
+  CanonicalCode,
+  INVALID_SPAN_ID,
+  INVALID_TRACE_ID,
+  NoopSpan,
+  TraceFlags,
+} from '../../src';
 
 describe('NoopSpan', () => {
   it('do not crash', () => {
diff --git a/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts b/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts
index 9fd5171dbd..ed017dda99 100644
--- a/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts
+++ b/packages/opentelemetry-api/test/noop-implementations/noop-tracer.test.ts
@@ -41,7 +41,10 @@ describe('NoopTracer', () => {
     assert.ok(httpTextFormat);
 
     httpTextFormat.inject(Context.ROOT_CONTEXT, {});
-    assert.deepStrictEqual(httpTextFormat.extract(Context.ROOT_CONTEXT, {}), Context.ROOT_CONTEXT);
+    assert.deepStrictEqual(
+      httpTextFormat.extract(Context.ROOT_CONTEXT, {}),
+      Context.ROOT_CONTEXT
+    );
 
     const binaryFormat = tracer.getBinaryFormat();
     assert.ok(binaryFormat);

From 02605b21d6b24d9c0d2b96bca9def78e619fb0c5 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 12:37:00 -0500
Subject: [PATCH 09/23] chore: bust cache

---
 .circleci/config.yml | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/.circleci/config.yml b/.circleci/config.yml
index e04d9f22ba..f5e726e02b 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -40,7 +40,7 @@ mysql_service: &mysql_service
     MYSQL_ROOT_PASSWORD: rootpw
 
 cache_1: &cache_1
-  key: npm-cache-01-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-FDF2088C
+  key: npm-cache-01-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-F267A71D
   paths:
     - ./node_modules
     - ./package-lock.json
@@ -60,7 +60,7 @@ cache_1: &cache_1
     - packages/opentelemetry-plugin-dns/node_modules
 
 cache_2: &cache_2
-  key: npm-cache-02-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-FDF2088C
+  key: npm-cache-02-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-F267A71D
   paths:
     - packages/opentelemetry-plugin-grpc/node_modules
     - packages/opentelemetry-plugin-http/node_modules
@@ -95,10 +95,10 @@ node_unit_tests: &node_unit_tests
           echo "CIRCLE_NODE_VERSION=${CIRCLE_NODE_VERSION}"
     - restore_cache:
         keys:
-          - npm-cache-01-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-FDF2088C
+          - npm-cache-01-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-F267A71D
     - restore_cache:
         keys:
-          - npm-cache-02-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-FDF2088C
+          - npm-cache-02-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-F267A71D
     - run:
         name: Install Root Dependencies
         command: npm install --ignore-scripts
@@ -135,10 +135,10 @@ browsers_unit_tests: &browsers_unit_tests
           echo "CIRCLE_NODE_VERSION=${CIRCLE_NODE_VERSION}"
     - restore_cache:
         keys:
-          - npm-cache-01-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-FDF2088C
+          - npm-cache-01-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-F267A71D
     - restore_cache:
         keys:
-          - npm-cache-02-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-FDF2088C
+          - npm-cache-02-{{ .Environment.CIRCLE_JOB }}-{{ checksum "/tmp/checksums.txt" }}-F267A71D
     - run:
         name: Install Root Dependencies
         command: npm install --ignore-scripts

From 7961494a25496be6b0429c0fd76838ebde933a38 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 14:09:09 -0500
Subject: [PATCH 10/23] chore: revert unnecessary changes from api package

---
 .../distributed_context/DistributedContext.ts | 29 ++++++++++++
 .../src/distributed_context/EntryValue.ts     | 45 +++++++++++++++++++
 packages/opentelemetry-api/src/index.ts       | 22 ++++-----
 .../src/metrics/BoundInstrument.ts            |  9 +++-
 .../opentelemetry-api/src/metrics/Metric.ts   | 14 +++++-
 .../src/metrics/NoopMeter.ts                  | 20 +++++++--
 .../opentelemetry-api/test/api/api.test.ts    | 20 ++++-----
 .../noop-implementations/noop-meter.test.ts   | 16 ++++---
 .../noop-implementations/noop-span.test.ts    |  8 +---
 packages/opentelemetry-api/tsconfig.json      |  3 +-
 .../src/BoundInstrument.ts                    |  6 ++-
 11 files changed, 149 insertions(+), 43 deletions(-)
 create mode 100644 packages/opentelemetry-api/src/distributed_context/DistributedContext.ts
 create mode 100644 packages/opentelemetry-api/src/distributed_context/EntryValue.ts

diff --git a/packages/opentelemetry-api/src/distributed_context/DistributedContext.ts b/packages/opentelemetry-api/src/distributed_context/DistributedContext.ts
new file mode 100644
index 0000000000..b06dcb8059
--- /dev/null
+++ b/packages/opentelemetry-api/src/distributed_context/DistributedContext.ts
@@ -0,0 +1,29 @@
+/*!
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { EntryValue } from './EntryValue';
+
+/**
+ * DistributedContext represents collection of entries. Each key of
+ * DistributedContext is associated with exactly one value. DistributedContext
+ * is serializable, to facilitate propagating it not only inside the process
+ * but also across process boundaries. DistributedContext is used to annotate
+ * telemetry with the name:value pair Entry. Those values can be used to add
+ * dimension to the metric or additional contest properties to logs and traces.
+ */
+export interface DistributedContext {
+  [entryKey: string]: EntryValue;
+}
diff --git a/packages/opentelemetry-api/src/distributed_context/EntryValue.ts b/packages/opentelemetry-api/src/distributed_context/EntryValue.ts
new file mode 100644
index 0000000000..cb0c58557e
--- /dev/null
+++ b/packages/opentelemetry-api/src/distributed_context/EntryValue.ts
@@ -0,0 +1,45 @@
+/*!
+ * Copyright 2019, OpenTelemetry Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * {@link EntryValue} contains properties associated with a {@link
+ * DistributedContext}.
+ */
+export interface EntryValue {
+  /** `String` value of the `EntryValue`. */
+  value: string;
+  /**
+   * ttl is an integer that represents number of hops an entry can
+   * propagate.
+   */
+  ttl?: EntryTtl;
+}
+
+/**
+ * EntryTtl is an integer that represents number of hops an entry can propagate.
+ *
+ * For now, ONLY special values (0 and -1) are supported.
+ */
+export enum EntryTtl {
+  /**
+   * NO_PROPAGATION is considered to have local scope and is used within the
+   * process it created.
+   */
+  NO_PROPAGATION = 0,
+
+  /** UNLIMITED_PROPAGATION can propagate unlimited hops. */
+  UNLIMITED_PROPAGATION = -1,
+}
diff --git a/packages/opentelemetry-api/src/index.ts b/packages/opentelemetry-api/src/index.ts
index 49a1d42e48..e35ac4e746 100644
--- a/packages/opentelemetry-api/src/index.ts
+++ b/packages/opentelemetry-api/src/index.ts
@@ -16,33 +16,35 @@
 
 export * from './common/Logger';
 export * from './common/Time';
-export * from './context/propagation/BinaryFormat';
 export * from './context/propagation/carrier';
+export * from './context/propagation/BinaryFormat';
 export * from './context/propagation/HttpTextFormat';
+export * from './distributed_context/DistributedContext';
+export * from './distributed_context/EntryValue';
 export * from './metrics/BoundInstrument';
 export * from './metrics/Meter';
 export * from './metrics/MeterProvider';
 export * from './metrics/Metric';
-export * from './metrics/NoopMeter';
-export * from './metrics/NoopMeterProvider';
 export * from './trace/attributes';
 export * from './trace/Event';
 export * from './trace/instrumentation/Plugin';
 export * from './trace/link';
-export * from './trace/NoopSpan';
-export * from './trace/NoopTracer';
-export * from './trace/NoopTracerProvider';
 export * from './trace/Sampler';
-export * from './trace/span_context';
-export * from './trace/span_kind';
 export * from './trace/span';
 export * from './trace/SpanOptions';
+export * from './trace/span_context';
+export * from './trace/span_kind';
 export * from './trace/status';
 export * from './trace/TimedEvent';
+export * from './trace/tracer';
+export * from './trace/tracer_provider';
 export * from './trace/trace_flags';
 export * from './trace/trace_state';
-export * from './trace/tracer_provider';
-export * from './trace/tracer';
+export * from './trace/NoopSpan';
+export * from './trace/NoopTracer';
+export * from './trace/NoopTracerProvider';
+export * from './metrics/NoopMeterProvider';
+export * from './metrics/NoopMeter';
 
 import { TraceAPI } from './api/trace';
 /** Entrypoint for trace API */
diff --git a/packages/opentelemetry-api/src/metrics/BoundInstrument.ts b/packages/opentelemetry-api/src/metrics/BoundInstrument.ts
index 284f6e4a8c..83612d6b4d 100644
--- a/packages/opentelemetry-api/src/metrics/BoundInstrument.ts
+++ b/packages/opentelemetry-api/src/metrics/BoundInstrument.ts
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+import { DistributedContext } from '../distributed_context/DistributedContext';
 import { SpanContext } from '../trace/span_context';
 
 /** An Instrument for Counter Metric. */
@@ -39,9 +40,15 @@ export interface BoundMeasure {
   /**
    * Records the given value to this measure.
    * @param value the measurement to record.
+   * @param distContext the distContext associated with the measurements.
    * @param spanContext the {@link SpanContext} that identifies the {@link Span}
    *     for which the measurements are associated with.
    */
   record(value: number): void;
-  record(value: number, spanContext: SpanContext): void;
+  record(value: number, distContext: DistributedContext): void;
+  record(
+    value: number,
+    distContext: DistributedContext,
+    spanContext: SpanContext
+  ): void;
 }
diff --git a/packages/opentelemetry-api/src/metrics/Metric.ts b/packages/opentelemetry-api/src/metrics/Metric.ts
index d35da4fa7c..0c6ca61a70 100644
--- a/packages/opentelemetry-api/src/metrics/Metric.ts
+++ b/packages/opentelemetry-api/src/metrics/Metric.ts
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+import { DistributedContext } from '../distributed_context/DistributedContext';
 import { SpanContext } from '../trace/span_context';
 
 /**
@@ -122,7 +123,18 @@ export interface MetricUtils {
    */
   record(value: number, labelSet: LabelSet): void;
 
-  record(value: number, labelSet: LabelSet, spanContext: SpanContext): void;
+  record(
+    value: number,
+    labelSet: LabelSet,
+    distContext: DistributedContext
+  ): void;
+
+  record(
+    value: number,
+    labelSet: LabelSet,
+    distContext: DistributedContext,
+    spanContext: SpanContext
+  ): void;
 }
 
 /**
diff --git a/packages/opentelemetry-api/src/metrics/NoopMeter.ts b/packages/opentelemetry-api/src/metrics/NoopMeter.ts
index 0c3ecfce26..c39a664aa5 100644
--- a/packages/opentelemetry-api/src/metrics/NoopMeter.ts
+++ b/packages/opentelemetry-api/src/metrics/NoopMeter.ts
@@ -17,6 +17,7 @@
 import { Meter } from './Meter';
 import { MetricOptions, Metric, Labels, LabelSet, MetricUtils } from './Metric';
 import { BoundMeasure, BoundCounter, BoundGauge } from './BoundInstrument';
+import { DistributedContext } from '../distributed_context/DistributedContext';
 import { SpanContext } from '../trace/span_context';
 
 /**
@@ -118,11 +119,18 @@ export class NoopGaugeMetric extends NoopMetric<BoundGauge>
 
 export class NoopMeasureMetric extends NoopMetric<BoundMeasure>
   implements Pick<MetricUtils, 'record'> {
-  record(value: number, labelSet: LabelSet, spanContext?: SpanContext) {
-    if (typeof spanContext === 'undefined') {
+  record(
+    value: number,
+    labelSet: LabelSet,
+    distContext?: DistributedContext,
+    spanContext?: SpanContext
+  ) {
+    if (typeof distContext === 'undefined') {
       this.bind(labelSet).record(value);
+    } else if (typeof spanContext === 'undefined') {
+      this.bind(labelSet).record(value, distContext);
     } else {
-      this.bind(labelSet).record(value, spanContext);
+      this.bind(labelSet).record(value, distContext, spanContext);
     }
   }
 }
@@ -140,7 +148,11 @@ export class NoopBoundGauge implements BoundGauge {
 }
 
 export class NoopBoundMeasure implements BoundMeasure {
-  record(value: number, spanContext?: SpanContext): void {
+  record(
+    value: number,
+    distContext?: DistributedContext,
+    spanContext?: SpanContext
+  ): void {
     return;
   }
 }
diff --git a/packages/opentelemetry-api/test/api/api.test.ts b/packages/opentelemetry-api/test/api/api.test.ts
index 031fa6f976..c0ecb9baf9 100644
--- a/packages/opentelemetry-api/test/api/api.test.ts
+++ b/packages/opentelemetry-api/test/api/api.test.ts
@@ -15,14 +15,7 @@
  */
 
 import * as assert from 'assert';
-import api, {
-  TraceFlags,
-  NoopSpan,
-  NoopTracerProvider,
-  NoopTracer,
-  SpanOptions,
-  Span,
-} from '../../src';
+import api, { TraceFlags, NoopSpan, NoopTracerProvider, NoopTracer, SpanOptions, Span } from '../../src';
 
 describe('API', () => {
   const functions = [
@@ -34,7 +27,7 @@ describe('API', () => {
   ];
 
   it('should expose a tracer provider via getTracerProvider', () => {
-    const tracer = api.trace.getTracerProvider();
+    const tracer =  api.trace.getTracerProvider();
     assert.ok(tracer);
     assert.strictEqual(typeof tracer, 'object');
   });
@@ -53,7 +46,7 @@ describe('API', () => {
 
     it('should not crash', () => {
       functions.forEach(fn => {
-        const tracer = api.trace.getTracerProvider();
+        const tracer =  api.trace.getTracerProvider();
         try {
           ((tracer as unknown) as { [fn: string]: Function })[fn](); // Try to run the function
           assert.ok(true, fn);
@@ -67,13 +60,16 @@ describe('API', () => {
 
     it('should use the global tracer provider', () => {
       api.trace.initGlobalTracerProvider(new TestTracerProvider());
-      const tracer = api.trace.getTracerProvider().getTracer('name');
+      const tracer =  api.trace.getTracerProvider().getTracer('name');
       const span = tracer.startSpan('test');
       assert.deepStrictEqual(span, dummySpan);
     });
 
     class TestTracer extends NoopTracer {
-      startSpan(name: string, options?: SpanOptions | undefined): Span {
+      startSpan(
+        name: string,
+        options?: SpanOptions | undefined
+      ): Span {
         return dummySpan;
       }
     }
diff --git a/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts b/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts
index 21cb6171f0..052854e82b 100644
--- a/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts
+++ b/packages/opentelemetry-api/test/noop-implementations/noop-meter.test.ts
@@ -23,9 +23,10 @@ import {
   NOOP_BOUND_MEASURE,
   NOOP_COUNTER_METRIC,
   NOOP_GAUGE_METRIC,
-  NOOP_MEASURE_METRIC,
+  NOOP_MEASURE_METRIC
 } from '../../src';
 
+
 describe('NoopMeter', () => {
   it('should not crash', () => {
     const meter = new NoopMeterProvider().getMeter('test-noop');
@@ -49,10 +50,15 @@ describe('NoopMeter', () => {
 
     const measure = meter.createMeasure('some-name');
     measure.getDefaultBound().record(1);
-    measure.getDefaultBound().record(1, {
-      traceId: 'a3cda95b652f4a1592b449d5929fda1b',
-      spanId: '5e0c63257de34c92',
-    });
+    measure.getDefaultBound().record(1, { key: { value: 'value' } });
+    measure.getDefaultBound().record(
+      1,
+      { key: { value: 'value' } },
+      {
+        traceId: 'a3cda95b652f4a1592b449d5929fda1b',
+        spanId: '5e0c63257de34c92',
+      }
+    );
 
     // ensure the correct noop const is returned
     assert.strictEqual(measure, NOOP_MEASURE_METRIC);
diff --git a/packages/opentelemetry-api/test/noop-implementations/noop-span.test.ts b/packages/opentelemetry-api/test/noop-implementations/noop-span.test.ts
index a42d471189..0350a9ab53 100644
--- a/packages/opentelemetry-api/test/noop-implementations/noop-span.test.ts
+++ b/packages/opentelemetry-api/test/noop-implementations/noop-span.test.ts
@@ -15,13 +15,7 @@
  */
 
 import * as assert from 'assert';
-import {
-  CanonicalCode,
-  INVALID_SPAN_ID,
-  INVALID_TRACE_ID,
-  NoopSpan,
-  TraceFlags,
-} from '../../src';
+import { CanonicalCode, INVALID_SPAN_ID, INVALID_TRACE_ID, NoopSpan, TraceFlags } from '../../src';
 
 describe('NoopSpan', () => {
   it('do not crash', () => {
diff --git a/packages/opentelemetry-api/tsconfig.json b/packages/opentelemetry-api/tsconfig.json
index df95d9cc57..2b05ed8413 100644
--- a/packages/opentelemetry-api/tsconfig.json
+++ b/packages/opentelemetry-api/tsconfig.json
@@ -5,8 +5,7 @@
     "outDir": "build"
   },
   "include": [
-    "src/**/*.ts",
-    "test/**/*.ts"
+    "src/**/*.ts"
   ],
   "typedocOptions": {
     "name": "OpenTelemetry API for JavaScript",
diff --git a/packages/opentelemetry-metrics/src/BoundInstrument.ts b/packages/opentelemetry-metrics/src/BoundInstrument.ts
index e78dca9576..b72176fae1 100644
--- a/packages/opentelemetry-metrics/src/BoundInstrument.ts
+++ b/packages/opentelemetry-metrics/src/BoundInstrument.ts
@@ -144,7 +144,11 @@ export class BoundMeasure extends BaseBoundInstrument
     super(labelSet);
   }
 
-  record(value: number, spanContext?: types.SpanContext): void {
+  record(
+    value: number,
+    distContext?: types.DistributedContext,
+    spanContext?: types.SpanContext
+  ): void {
     if (this._disabled) return;
 
     if (this._absolute && value < 0) {

From 02e07cb6962ba9104ae2409809255ad766556333 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 14:50:55 -0500
Subject: [PATCH 11/23] chore: revert carrier so it can be a separate pr

---
 .../src/context/propagation/HttpTextFormat.ts |  5 ++---
 .../context/propagation/NoopHttpTextFormat.ts |  5 ++---
 .../src/context/propagation/carrier.ts        | 19 -------------------
 packages/opentelemetry-api/src/index.ts       |  1 -
 .../src/shim.ts                               |  5 ++---
 5 files changed, 6 insertions(+), 29 deletions(-)
 delete mode 100644 packages/opentelemetry-api/src/context/propagation/carrier.ts

diff --git a/packages/opentelemetry-api/src/context/propagation/HttpTextFormat.ts b/packages/opentelemetry-api/src/context/propagation/HttpTextFormat.ts
index fef9293ecf..a8111400ae 100644
--- a/packages/opentelemetry-api/src/context/propagation/HttpTextFormat.ts
+++ b/packages/opentelemetry-api/src/context/propagation/HttpTextFormat.ts
@@ -15,7 +15,6 @@
  */
 
 import { Context } from '@opentelemetry/scope-base';
-import { Carrier } from './carrier';
 
 /**
  * Injects {@link Context} into and extracts it from carriers that travel
@@ -35,7 +34,7 @@ export interface HttpTextFormat {
    * @param context the Context from which to extract values to transmit over the wire.
    * @param carrier the carrier of propagation fields, such as http request headers.
    */
-  inject(context: Context, carrier: Carrier): void;
+  inject(context: Context, carrier: unknown): void;
 
   /**
    * Given a {@link Context} and a carrier, extract context values from a carrier and
@@ -44,5 +43,5 @@ export interface HttpTextFormat {
    * @param context the Context from which to extract values to transmit over the wire.
    * @param carrier the carrier of propagation fields, such as http request headers.
    */
-  extract(context: Context, carrier: Carrier): Context;
+  extract(context: Context, carrier: unknown): Context;
 }
diff --git a/packages/opentelemetry-api/src/context/propagation/NoopHttpTextFormat.ts b/packages/opentelemetry-api/src/context/propagation/NoopHttpTextFormat.ts
index 1f38729eb5..7296ffdf9b 100644
--- a/packages/opentelemetry-api/src/context/propagation/NoopHttpTextFormat.ts
+++ b/packages/opentelemetry-api/src/context/propagation/NoopHttpTextFormat.ts
@@ -15,7 +15,6 @@
  */
 
 import { Context } from '@opentelemetry/scope-base';
-import { Carrier } from './carrier';
 import { HttpTextFormat } from './HttpTextFormat';
 
 /**
@@ -23,9 +22,9 @@ import { HttpTextFormat } from './HttpTextFormat';
  */
 export class NoopHttpTextFormat implements HttpTextFormat {
   /** Noop inject function does nothing */
-  inject(context: Context, carrier: Carrier): void {}
+  inject(context: Context, carrier: unknown): void {}
   /** Noop extract function does nothing and returns the input context */
-  extract(context: Context, carrier: Carrier): Context {
+  extract(context: Context, carrier: unknown): Context {
     return context;
   }
 }
diff --git a/packages/opentelemetry-api/src/context/propagation/carrier.ts b/packages/opentelemetry-api/src/context/propagation/carrier.ts
deleted file mode 100644
index 7644ace1af..0000000000
--- a/packages/opentelemetry-api/src/context/propagation/carrier.ts
+++ /dev/null
@@ -1,19 +0,0 @@
-/*!
- * Copyright 2020, OpenTelemetry Authors
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      https://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-export type Carrier = {
-  [key: string]: unknown;
-};
diff --git a/packages/opentelemetry-api/src/index.ts b/packages/opentelemetry-api/src/index.ts
index e35ac4e746..ab10bb7ed4 100644
--- a/packages/opentelemetry-api/src/index.ts
+++ b/packages/opentelemetry-api/src/index.ts
@@ -16,7 +16,6 @@
 
 export * from './common/Logger';
 export * from './common/Time';
-export * from './context/propagation/carrier';
 export * from './context/propagation/BinaryFormat';
 export * from './context/propagation/HttpTextFormat';
 export * from './distributed_context/DistributedContext';
diff --git a/packages/opentelemetry-shim-opentracing/src/shim.ts b/packages/opentelemetry-shim-opentracing/src/shim.ts
index 7fdf9b1044..9fa2a0cc9e 100644
--- a/packages/opentelemetry-shim-opentracing/src/shim.ts
+++ b/packages/opentelemetry-shim-opentracing/src/shim.ts
@@ -15,7 +15,6 @@
  */
 
 import * as types from '@opentelemetry/api';
-import { Carrier } from '@opentelemetry/api';
 import { Context, NoopLogger } from '@opentelemetry/core';
 import * as opentracing from 'opentracing';
 
@@ -121,7 +120,7 @@ export class TracerShim extends opentracing.Tracer {
   _inject(
     spanContext: opentracing.SpanContext,
     format: string,
-    carrier: Carrier
+    carrier: unknown
   ): void {
     const opentelemSpanContext: types.SpanContext = (spanContext as SpanContextShim).getSpanContext();
     if (!carrier || typeof carrier !== 'object') return;
@@ -149,7 +148,7 @@ export class TracerShim extends opentracing.Tracer {
     }
   }
 
-  _extract(format: string, carrier: Carrier): opentracing.SpanContext | null {
+  _extract(format: string, carrier: unknown): opentracing.SpanContext | null {
     switch (format) {
       // tslint:disable-next-line:no-switch-case-fall-through
       case opentracing.FORMAT_HTTP_HEADERS:

From fb0d170c88f5447e56611f88bbd0891f3f938ab7 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 15:18:24 -0500
Subject: [PATCH 12/23] chore: typo

---
 packages/opentelemetry-plugin-http/src/http.ts            | 4 ++--
 packages/opentelemetry-plugin-xml-http-request/src/xhr.ts | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/opentelemetry-plugin-http/src/http.ts b/packages/opentelemetry-plugin-http/src/http.ts
index e2abb4e369..b5c3937b2c 100644
--- a/packages/opentelemetry-plugin-http/src/http.ts
+++ b/packages/opentelemetry-plugin-http/src/http.ts
@@ -297,7 +297,7 @@ export class HttpPlugin extends BasePlugin<Http> {
         }),
       };
 
-      // Using context direclty like this is temporary. In a future PR, context
+      // Using context directly like this is temporary. In a future PR, context
       // will be managed by the scope manager (which may be renamed to context manager?)
       const spanContext = Context.getExtractedSpanContext(
         propagation.extract(Context.ROOT_CONTEXT, headers)
@@ -410,7 +410,7 @@ export class HttpPlugin extends BasePlugin<Http> {
       const span = plugin._startHttpSpan(operationName, spanOptions);
       plugin._tracer
         .getHttpTextFormat()
-        // Using context direclty like this is temporary. In a future PR, context
+        // Using context directly like this is temporary. In a future PR, context
         // will be managed by the scope manager (which may be renamed to context manager?)
         .inject(
           Context.setActiveSpan(Context.ROOT_CONTEXT, span),
diff --git a/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts b/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
index 80c97c4ccf..70aa3bb7ef 100644
--- a/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
+++ b/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
@@ -90,7 +90,7 @@ export class XMLHttpRequestPlugin extends BasePlugin<XMLHttpRequest> {
     const headers: { [key: string]: unknown } = {};
     this._tracer
       .getHttpTextFormat()
-      // Using context direclty like this is temporary. In a future PR, context
+      // Using context directly like this is temporary. In a future PR, context
       // will be managed by the scope manager (which may be renamed to context manager?)
       .inject(Context.setActiveSpan(Context.ROOT_CONTEXT, span), headers);
 

From d4335289d3a9b372e5ceb0bbdc55c848a7b39373 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 17:05:06 -0500
Subject: [PATCH 13/23] chore: avoid extra allocation on context set value

---
 packages/opentelemetry-scope-base/src/context.ts | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
index 6b413e88b2..f4bfab021a 100644
--- a/packages/opentelemetry-scope-base/src/context.ts
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -32,9 +32,8 @@ export class Context {
    *
    * @param context a context from which to inherit values
    */
-  protected constructor(context: Context | Store = {}) {
-    const storage = context instanceof Context ? context._context : context;
-    this._context = Object.assign(Object.create(null), storage);
+  protected constructor(parentContext: Store = {}) {
+    this._context = Object.assign(Object.create(null), parentContext);
   }
 
   /**
@@ -54,10 +53,9 @@ export class Context {
    * @param value value to set for the given key
    */
   setValue(key: string, value: unknown): Context {
-    return new Context({
-      ...this._context,
-      [key]: value,
-    });
+    const context = new Context(this._context);
+    context._context[key] = value;
+    return context
   }
 
   /**
@@ -67,7 +65,7 @@ export class Context {
    * @param key context key for which to clear a value
    */
   deleteValue(key: string): Context {
-    const context = new Context(this);
+    const context = new Context(this._context);
     delete context._context[key];
     return context;
   }

From 38cda1d05214f1b2976c0b10ee1b1306077e70f3 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Thu, 6 Feb 2020 17:07:31 -0500
Subject: [PATCH 14/23] chore: lint

---
 packages/opentelemetry-scope-base/src/context.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
index f4bfab021a..aeb809bb1c 100644
--- a/packages/opentelemetry-scope-base/src/context.ts
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -55,7 +55,7 @@ export class Context {
   setValue(key: string, value: unknown): Context {
     const context = new Context(this._context);
     context._context[key] = value;
-    return context
+    return context;
   }
 
   /**

From d4caaba6e90b18db558be2d552188b9f87d7eeb1 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Fri, 7 Feb 2020 10:27:37 -0500
Subject: [PATCH 15/23] chore: do not extend context

---
 packages/opentelemetry-api/src/index.ts       |   2 +
 .../opentelemetry-core/src/context/context.ts | 105 ++++++++----------
 .../src/context/propagation/B3Format.ts       |   7 +-
 .../context/propagation/HttpTraceContext.ts   |   7 +-
 .../test/context/B3Format.test.ts             |  34 +++---
 .../test/context/HttpTraceContext.test.ts     |  24 ++--
 .../opentelemetry-plugin-http/src/http.ts     |  15 ++-
 .../test/utils/DummyPropagation.ts            |  11 +-
 .../opentelemetry-plugin-https/package.json   |   1 -
 .../test/utils/DummyPropagation.ts            |  11 +-
 .../src/xhr.ts                                |   8 +-
 .../src/JaegerHttpTraceFormat.ts              |  16 ++-
 .../test/JaegerHttpTraceFormat.test.ts        |  23 ++--
 .../opentelemetry-scope-base/src/context.ts   |  17 +--
 .../src/shim.ts                               |  14 ++-
 packages/opentelemetry-tracing/src/Tracer.ts  |  21 ++--
 .../test/BasicTracerRegistry.test.ts          |   6 +-
 .../src/StackScopeManager.ts                  |   2 +-
 .../test/StackScopeManager.test.ts            |   2 +-
 19 files changed, 178 insertions(+), 148 deletions(-)

diff --git a/packages/opentelemetry-api/src/index.ts b/packages/opentelemetry-api/src/index.ts
index ab10bb7ed4..ffdf3667d6 100644
--- a/packages/opentelemetry-api/src/index.ts
+++ b/packages/opentelemetry-api/src/index.ts
@@ -45,6 +45,8 @@ export * from './trace/NoopTracerProvider';
 export * from './metrics/NoopMeterProvider';
 export * from './metrics/NoopMeter';
 
+export { Context } from '@opentelemetry/scope-base';
+
 import { TraceAPI } from './api/trace';
 /** Entrypoint for trace API */
 export const trace = TraceAPI.getInstance();
diff --git a/packages/opentelemetry-core/src/context/context.ts b/packages/opentelemetry-core/src/context/context.ts
index b404664423..e1fec8b8b8 100644
--- a/packages/opentelemetry-core/src/context/context.ts
+++ b/packages/opentelemetry-core/src/context/context.ts
@@ -15,67 +15,60 @@
  */
 
 import { Span, SpanContext } from '@opentelemetry/api';
-import { Context as ContextBase } from '@opentelemetry/scope-base';
+import { Context } from '@opentelemetry/scope-base';
 
 /**
- * Context class with static helper functions for accessing values
- * of cross-cutting concerns.
+ * Return the active span if one exists
+ *
+ * @param context context to get span from
  */
-export class Context extends ContextBase {
-  /**
-   * Return the active span if one exists
-   *
-   * @param context context to get span from
-   */
-  static getActiveSpan(context: Context): Span | undefined {
-    return (context.getValue('ACTIVE_SPAN') as Span) || undefined;
-  }
+export function getActiveSpan(context: Context): Span | undefined {
+  return (context.getValue('ACTIVE_SPAN') as Span) || undefined;
+}
 
-  /**
-   * Set the active span on a context
-   *
-   * @param context context to use as parent
-   * @param span span to set active
-   */
-  static setActiveSpan(context: Context, span: Span): Context {
-    return context.setValue('ACTIVE_SPAN', span);
-  }
+/**
+ * Set the active span on a context
+ *
+ * @param context context to use as parent
+ * @param span span to set active
+ */
+export function setActiveSpan(context: Context, span: Span): Context {
+  return context.setValue('ACTIVE_SPAN', span);
+}
 
-  /**
-   * Get the extracted span context from a context
-   *
-   * @param context context to get span context from
-   */
-  static getExtractedSpanContext(context: Context): SpanContext | undefined {
-    return (
-      (context.getValue('EXTRACTED_SPAN_CONTEXT') as SpanContext) || undefined
-    );
-  }
+/**
+ * Get the extracted span context from a context
+ *
+ * @param context context to get span context from
+ */
+export function getExtractedSpanContext(
+  context: Context
+): SpanContext | undefined {
+  return (
+    (context.getValue('EXTRACTED_SPAN_CONTEXT') as SpanContext) || undefined
+  );
+}
 
-  /**
-   * Set the extracted span context on a context
-   *
-   * @param context context to set span context on
-   * @param spanContext span context to set
-   */
-  static setExtractedSpanContext(
-    context: Context,
-    spanContext: SpanContext
-  ): Context {
-    return context.setValue('EXTRACTED_SPAN_CONTEXT', spanContext);
-  }
+/**
+ * Set the extracted span context on a context
+ *
+ * @param context context to set span context on
+ * @param spanContext span context to set
+ */
+export function setExtractedSpanContext(
+  context: Context,
+  spanContext: SpanContext
+): Context {
+  return context.setValue('EXTRACTED_SPAN_CONTEXT', spanContext);
+}
 
-  /**
-   * Get the span context of the parent span if it exists,
-   * or the extracted span context if there is no active
-   * span.
-   *
-   * @param context context to get values from
-   */
-  static getParentSpanContext(context: Context) {
-    return (
-      Context.getActiveSpan(context)?.context() ||
-      Context.getExtractedSpanContext(context)
-    );
-  }
+/**
+ * Get the span context of the parent span if it exists,
+ * or the extracted span context if there is no active
+ * span.
+ *
+ * @param context context to get values from
+ */
+export function getParentSpanContext(context: Context) {
+  return getActiveSpan(context)?.context() || getExtractedSpanContext(context);
 }
diff --git a/packages/opentelemetry-core/src/context/propagation/B3Format.ts b/packages/opentelemetry-core/src/context/propagation/B3Format.ts
index 5b3db96594..dd9e7319de 100644
--- a/packages/opentelemetry-core/src/context/propagation/B3Format.ts
+++ b/packages/opentelemetry-core/src/context/propagation/B3Format.ts
@@ -15,7 +15,8 @@
  */
 
 import { HttpTextFormat, TraceFlags } from '@opentelemetry/api';
-import { Context } from '../context';
+import { Context } from '@opentelemetry/scope-base';
+import { getParentSpanContext, setExtractedSpanContext } from '../context';
 
 export const X_B3_TRACE_ID = 'x-b3-traceid';
 export const X_B3_SPAN_ID = 'x-b3-spanid';
@@ -38,7 +39,7 @@ function isValidSpanId(spanId: string): boolean {
  */
 export class B3Format implements HttpTextFormat {
   inject(context: Context, carrier: { [key: string]: unknown }) {
-    const spanContext = Context.getParentSpanContext(context);
+    const spanContext = getParentSpanContext(context);
     if (!spanContext) return;
 
     if (
@@ -70,7 +71,7 @@ export class B3Format implements HttpTextFormat {
       : sampledHeader;
 
     if (isValidTraceId(traceId) && isValidSpanId(spanId)) {
-      return Context.setExtractedSpanContext(context, {
+      return setExtractedSpanContext(context, {
         traceId,
         spanId,
         isRemote: true,
diff --git a/packages/opentelemetry-core/src/context/propagation/HttpTraceContext.ts b/packages/opentelemetry-core/src/context/propagation/HttpTraceContext.ts
index fa70fbe1d2..f3f342b356 100644
--- a/packages/opentelemetry-core/src/context/propagation/HttpTraceContext.ts
+++ b/packages/opentelemetry-core/src/context/propagation/HttpTraceContext.ts
@@ -15,8 +15,9 @@
  */
 
 import { HttpTextFormat, SpanContext, TraceFlags } from '@opentelemetry/api';
+import { Context } from '@opentelemetry/scope-base';
 import { TraceState } from '../../trace/TraceState';
-import { Context } from '../context';
+import { getParentSpanContext, setExtractedSpanContext } from '../context';
 
 export const TRACE_PARENT_HEADER = 'traceparent';
 export const TRACE_STATE_HEADER = 'tracestate';
@@ -58,7 +59,7 @@ export function parseTraceParent(traceParent: string): SpanContext | null {
  */
 export class HttpTraceContext implements HttpTextFormat {
   inject(context: Context, carrier: { [key: string]: unknown }) {
-    const spanContext = Context.getParentSpanContext(context);
+    const spanContext = getParentSpanContext(context);
     if (!spanContext) return;
 
     const traceParent = `${VERSION}-${spanContext.traceId}-${
@@ -91,6 +92,6 @@ export class HttpTraceContext implements HttpTextFormat {
         : traceStateHeader;
       spanContext.traceState = new TraceState(state as string);
     }
-    return Context.setExtractedSpanContext(context, spanContext);
+    return setExtractedSpanContext(context, spanContext);
   }
 }
diff --git a/packages/opentelemetry-core/test/context/B3Format.test.ts b/packages/opentelemetry-core/test/context/B3Format.test.ts
index ea352f24cc..df7a1e6162 100644
--- a/packages/opentelemetry-core/test/context/B3Format.test.ts
+++ b/packages/opentelemetry-core/test/context/B3Format.test.ts
@@ -16,7 +16,11 @@
 
 import { SpanContext, TraceFlags } from '@opentelemetry/api';
 import * as assert from 'assert';
-import { Context } from '../../src/context/context';
+import {
+  setExtractedSpanContext,
+  getExtractedSpanContext,
+} from '../../src/context/context';
+import { Context } from '@opentelemetry/scope-base';
 import {
   B3Format,
   X_B3_SAMPLED,
@@ -42,7 +46,7 @@ describe('B3Format', () => {
       };
 
       b3Format.inject(
-        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
         carrier
       );
       assert.deepStrictEqual(
@@ -63,7 +67,7 @@ describe('B3Format', () => {
       };
 
       b3Format.inject(
-        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
         carrier
       );
       assert.deepStrictEqual(
@@ -80,7 +84,7 @@ describe('B3Format', () => {
         spanId: '',
       };
       b3Format.inject(
-        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, emptySpanContext),
+        setExtractedSpanContext(Context.ROOT_CONTEXT, emptySpanContext),
         carrier
       );
       assert.deepStrictEqual(carrier[X_B3_TRACE_ID], undefined);
@@ -94,7 +98,7 @@ describe('B3Format', () => {
       };
 
       b3Format.inject(
-        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
         carrier
       );
       assert.deepStrictEqual(
@@ -110,7 +114,7 @@ describe('B3Format', () => {
     it('should extract context of a unsampled span from carrier', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         b3Format.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -126,7 +130,7 @@ describe('B3Format', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
       carrier[X_B3_SAMPLED] = '1';
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         b3Format.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -142,7 +146,7 @@ describe('B3Format', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
       carrier[X_B3_SAMPLED] = true;
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         b3Format.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -158,7 +162,7 @@ describe('B3Format', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
       carrier[X_B3_SAMPLED] = false;
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         b3Format.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -174,7 +178,7 @@ describe('B3Format', () => {
       carrier[X_B3_TRACE_ID] = undefined;
       carrier[X_B3_SPAN_ID] = undefined;
       assert.deepStrictEqual(
-        Context.getExtractedSpanContext(
+        getExtractedSpanContext(
           b3Format.extract(Context.ROOT_CONTEXT, carrier)
         ),
         undefined
@@ -185,7 +189,7 @@ describe('B3Format', () => {
       carrier[X_B3_TRACE_ID] = '0af7651916cd43dd8448eb211c80319c';
       carrier[X_B3_SPAN_ID] = undefined;
       assert.deepStrictEqual(
-        Context.getExtractedSpanContext(
+        getExtractedSpanContext(
           b3Format.extract(Context.ROOT_CONTEXT, carrier)
         ),
         undefined
@@ -194,7 +198,7 @@ describe('B3Format', () => {
 
     it('returns undefined if b3 header is missing', () => {
       assert.deepStrictEqual(
-        Context.getExtractedSpanContext(
+        getExtractedSpanContext(
           b3Format.extract(Context.ROOT_CONTEXT, carrier)
         ),
         undefined
@@ -204,7 +208,7 @@ describe('B3Format', () => {
     it('returns undefined if b3 header is invalid', () => {
       carrier[X_B3_TRACE_ID] = 'invalid!';
       assert.deepStrictEqual(
-        Context.getExtractedSpanContext(
+        getExtractedSpanContext(
           b3Format.extract(Context.ROOT_CONTEXT, carrier)
         ),
         undefined
@@ -215,7 +219,7 @@ describe('B3Format', () => {
       carrier[X_B3_TRACE_ID] = ['0af7651916cd43dd8448eb211c80319c'];
       carrier[X_B3_SPAN_ID] = 'b7ad6b7169203331';
       carrier[X_B3_SAMPLED] = '01';
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         b3Format.extract(Context.ROOT_CONTEXT, carrier)
       );
       assert.deepStrictEqual(extractedSpanContext, {
@@ -266,7 +270,7 @@ describe('B3Format', () => {
       Object.getOwnPropertyNames(testCases).forEach(testCase => {
         carrier[X_B3_TRACE_ID] = testCases[testCase];
 
-        const extractedSpanContext = Context.getExtractedSpanContext(
+        const extractedSpanContext = getExtractedSpanContext(
           b3Format.extract(Context.ROOT_CONTEXT, carrier)
         );
         assert.deepStrictEqual(extractedSpanContext, undefined, testCase);
diff --git a/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts b/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts
index 83dccac40b..fb53cec343 100644
--- a/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts
+++ b/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts
@@ -15,8 +15,12 @@
  */
 
 import { SpanContext, TraceFlags } from '@opentelemetry/api';
+import { Context } from '@opentelemetry/scope-base';
 import * as assert from 'assert';
-import { Context } from '../../src/context/context';
+import {
+  getExtractedSpanContext,
+  setExtractedSpanContext,
+} from '../../src/context/context';
 import {
   HttpTraceContext,
   TRACE_PARENT_HEADER,
@@ -41,7 +45,7 @@ describe('HttpTraceContext', () => {
       };
 
       httpTraceContext.inject(
-        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
         carrier
       );
       assert.deepStrictEqual(
@@ -60,7 +64,7 @@ describe('HttpTraceContext', () => {
       };
 
       httpTraceContext.inject(
-        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
         carrier
       );
       assert.deepStrictEqual(
@@ -75,7 +79,7 @@ describe('HttpTraceContext', () => {
     it('should extract context of a sampled span from carrier', () => {
       carrier[TRACE_PARENT_HEADER] =
         '00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01';
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -89,7 +93,7 @@ describe('HttpTraceContext', () => {
 
     it('returns null if traceparent header is missing', () => {
       assert.deepStrictEqual(
-        Context.getExtractedSpanContext(
+        getExtractedSpanContext(
           httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
         ),
         undefined
@@ -99,7 +103,7 @@ describe('HttpTraceContext', () => {
     it('returns null if traceparent header is invalid', () => {
       carrier[TRACE_PARENT_HEADER] = 'invalid!';
       assert.deepStrictEqual(
-        Context.getExtractedSpanContext(
+        getExtractedSpanContext(
           httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
         ),
         undefined
@@ -110,7 +114,7 @@ describe('HttpTraceContext', () => {
       carrier[TRACE_PARENT_HEADER] = [
         '00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01',
       ];
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
       );
       assert.deepStrictEqual(extractedSpanContext, {
@@ -125,7 +129,7 @@ describe('HttpTraceContext', () => {
       carrier[TRACE_PARENT_HEADER] =
         '00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01';
       carrier[TRACE_STATE_HEADER] = 'foo=bar,baz=qux';
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -143,7 +147,7 @@ describe('HttpTraceContext', () => {
       carrier[TRACE_PARENT_HEADER] =
         '00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01';
       carrier[TRACE_STATE_HEADER] = ['foo=bar,baz=qux', 'quux=quuz'];
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
       );
       assert.deepStrictEqual(extractedSpanContext, {
@@ -195,7 +199,7 @@ describe('HttpTraceContext', () => {
       Object.getOwnPropertyNames(testCases).forEach(testCase => {
         carrier[TRACE_PARENT_HEADER] = testCases[testCase];
 
-        const extractedSpanContext = Context.getExtractedSpanContext(
+        const extractedSpanContext = getExtractedSpanContext(
           httpTraceContext.extract(Context.ROOT_CONTEXT, carrier)
         );
         assert.deepStrictEqual(extractedSpanContext, undefined, testCase);
diff --git a/packages/opentelemetry-plugin-http/src/http.ts b/packages/opentelemetry-plugin-http/src/http.ts
index b5c3937b2c..19c9cb7a6f 100644
--- a/packages/opentelemetry-plugin-http/src/http.ts
+++ b/packages/opentelemetry-plugin-http/src/http.ts
@@ -16,12 +16,18 @@
 
 import {
   CanonicalCode,
+  Context,
   Span,
   SpanKind,
   SpanOptions,
   Status,
 } from '@opentelemetry/api';
-import { BasePlugin, Context, isValid } from '@opentelemetry/core';
+import {
+  BasePlugin,
+  getExtractedSpanContext,
+  isValid,
+  setActiveSpan,
+} from '@opentelemetry/core';
 import {
   ClientRequest,
   IncomingMessage,
@@ -299,7 +305,7 @@ export class HttpPlugin extends BasePlugin<Http> {
 
       // Using context directly like this is temporary. In a future PR, context
       // will be managed by the scope manager (which may be renamed to context manager?)
-      const spanContext = Context.getExtractedSpanContext(
+      const spanContext = getExtractedSpanContext(
         propagation.extract(Context.ROOT_CONTEXT, headers)
       );
       if (spanContext && isValid(spanContext)) {
@@ -412,10 +418,7 @@ export class HttpPlugin extends BasePlugin<Http> {
         .getHttpTextFormat()
         // Using context directly like this is temporary. In a future PR, context
         // will be managed by the scope manager (which may be renamed to context manager?)
-        .inject(
-          Context.setActiveSpan(Context.ROOT_CONTEXT, span),
-          options.headers!
-        );
+        .inject(setActiveSpan(Context.ROOT_CONTEXT, span), options.headers!);
 
       const request: ClientRequest = plugin._safeExecute(
         span,
diff --git a/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts b/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts
index 9101ab7d3c..887b7127a0 100644
--- a/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts
+++ b/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts
@@ -13,21 +13,24 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import { HttpTextFormat } from '@opentelemetry/api';
-import { Context } from '@opentelemetry/core';
+import { Context, HttpTextFormat } from '@opentelemetry/api';
+import {
+  setExtractedSpanContext,
+  getParentSpanContext,
+} from '@opentelemetry/core';
 import * as http from 'http';
 
 export class DummyPropagation implements HttpTextFormat {
   static TRACE_CONTEXT_KEY = 'x-dummy-trace-id';
   static SPAN_CONTEXT_KEY = 'x-dummy-span-id';
   extract(context: Context, carrier: http.OutgoingHttpHeaders) {
-    return Context.setExtractedSpanContext(Context.ROOT_CONTEXT, {
+    return setExtractedSpanContext(Context.ROOT_CONTEXT, {
       traceId: carrier[DummyPropagation.TRACE_CONTEXT_KEY] as string,
       spanId: DummyPropagation.SPAN_CONTEXT_KEY,
     });
   }
   inject(context: Context, headers: { [custom: string]: string }): void {
-    const spanContext = Context.getParentSpanContext(context);
+    const spanContext = getParentSpanContext(context);
     if (!spanContext) return;
     headers[DummyPropagation.TRACE_CONTEXT_KEY] = spanContext.traceId;
     headers[DummyPropagation.SPAN_CONTEXT_KEY] = spanContext.spanId;
diff --git a/packages/opentelemetry-plugin-https/package.json b/packages/opentelemetry-plugin-https/package.json
index ce24710c22..6e179098db 100644
--- a/packages/opentelemetry-plugin-https/package.json
+++ b/packages/opentelemetry-plugin-https/package.json
@@ -42,7 +42,6 @@
   },
   "devDependencies": {
     "@opentelemetry/node": "^0.4.0",
-    "@opentelemetry/scope-base": "^0.4.0",
     "@opentelemetry/tracing": "^0.4.0",
     "@types/got": "^9.6.7",
     "@types/mocha": "^5.2.7",
diff --git a/packages/opentelemetry-plugin-https/test/utils/DummyPropagation.ts b/packages/opentelemetry-plugin-https/test/utils/DummyPropagation.ts
index 7bf3510ea7..5c65bd16d7 100644
--- a/packages/opentelemetry-plugin-https/test/utils/DummyPropagation.ts
+++ b/packages/opentelemetry-plugin-https/test/utils/DummyPropagation.ts
@@ -13,21 +13,24 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import { HttpTextFormat } from '@opentelemetry/api';
-import { Context } from '@opentelemetry/core';
+import { Context, HttpTextFormat } from '@opentelemetry/api';
+import {
+  setExtractedSpanContext,
+  getParentSpanContext,
+} from '@opentelemetry/core';
 import * as http from 'http';
 
 export class DummyPropagation implements HttpTextFormat {
   static TRACE_CONTEXT_KEY = 'x-dummy-trace-id';
   static SPAN_CONTEXT_KEY = 'x-dummy-span-id';
   extract(context: Context, carrier: http.OutgoingHttpHeaders) {
-    return Context.setExtractedSpanContext(context, {
+    return setExtractedSpanContext(context, {
       traceId: carrier[DummyPropagation.TRACE_CONTEXT_KEY] as string,
       spanId: DummyPropagation.SPAN_CONTEXT_KEY,
     });
   }
   inject(context: Context, headers: { [custom: string]: string }): void {
-    const spanContext = Context.getParentSpanContext(context);
+    const spanContext = getParentSpanContext(context);
     if (!spanContext) return;
     headers[DummyPropagation.TRACE_CONTEXT_KEY] = spanContext.traceId;
     headers[DummyPropagation.SPAN_CONTEXT_KEY] = spanContext.spanId;
diff --git a/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts b/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
index 70aa3bb7ef..8aea846312 100644
--- a/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
+++ b/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
@@ -14,16 +14,16 @@
  * limitations under the License.
  */
 
+import * as types from '@opentelemetry/api';
 import {
   BasePlugin,
-  Context,
   hrTime,
   isUrlIgnored,
   isWrapped,
   otperformance,
+  setActiveSpan,
   urlMatches,
 } from '@opentelemetry/core';
-import * as types from '@opentelemetry/api';
 import {
   addSpanNetworkEvent,
   getResource,
@@ -90,9 +90,9 @@ export class XMLHttpRequestPlugin extends BasePlugin<XMLHttpRequest> {
     const headers: { [key: string]: unknown } = {};
     this._tracer
       .getHttpTextFormat()
-      // Using context directly like this is temporary. In a future PR, context
+      // Using context direclty like this is temporary. In a future PR, context
       // will be managed by the scope manager (which may be renamed to context manager?)
-      .inject(Context.setActiveSpan(Context.ROOT_CONTEXT, span), headers);
+      .inject(setActiveSpan(types.Context.ROOT_CONTEXT, span), headers);
 
     Object.keys(headers).forEach(key => {
       xhr.setRequestHeader(key, String(headers[key]));
diff --git a/packages/opentelemetry-propagator-jaeger/src/JaegerHttpTraceFormat.ts b/packages/opentelemetry-propagator-jaeger/src/JaegerHttpTraceFormat.ts
index 6fb7c78b0a..05e5980915 100644
--- a/packages/opentelemetry-propagator-jaeger/src/JaegerHttpTraceFormat.ts
+++ b/packages/opentelemetry-propagator-jaeger/src/JaegerHttpTraceFormat.ts
@@ -14,8 +14,16 @@
  * limitations under the License.
  */
 
-import { HttpTextFormat, SpanContext, TraceFlags } from '@opentelemetry/api';
-import { Context } from '@opentelemetry/core';
+import {
+  Context,
+  HttpTextFormat,
+  SpanContext,
+  TraceFlags,
+} from '@opentelemetry/api';
+import {
+  getParentSpanContext,
+  setExtractedSpanContext,
+} from '@opentelemetry/core';
 
 export const UBER_TRACE_ID_HEADER = 'uber-trace-id';
 
@@ -45,7 +53,7 @@ export class JaegerHttpTraceFormat implements HttpTextFormat {
   }
 
   inject(context: Context, carrier: { [key: string]: unknown }) {
-    const spanContext = Context.getParentSpanContext(context);
+    const spanContext = getParentSpanContext(context);
     if (!spanContext) return;
 
     const traceFlags = `0${(
@@ -67,7 +75,7 @@ export class JaegerHttpTraceFormat implements HttpTextFormat {
     const spanContext = deserializeSpanContext(uberTraceId);
     if (!spanContext) return context;
 
-    return Context.setExtractedSpanContext(context, spanContext);
+    return setExtractedSpanContext(context, spanContext);
   }
 }
 
diff --git a/packages/opentelemetry-propagator-jaeger/test/JaegerHttpTraceFormat.test.ts b/packages/opentelemetry-propagator-jaeger/test/JaegerHttpTraceFormat.test.ts
index f641ebdf6d..c8e5e1b406 100644
--- a/packages/opentelemetry-propagator-jaeger/test/JaegerHttpTraceFormat.test.ts
+++ b/packages/opentelemetry-propagator-jaeger/test/JaegerHttpTraceFormat.test.ts
@@ -14,8 +14,11 @@
  * limitations under the License.
  */
 
-import { SpanContext, TraceFlags } from '@opentelemetry/api';
-import { Context } from '@opentelemetry/core';
+import { Context, SpanContext, TraceFlags } from '@opentelemetry/api';
+import {
+  getExtractedSpanContext,
+  setExtractedSpanContext,
+} from '@opentelemetry/core';
 import * as assert from 'assert';
 import {
   JaegerHttpTraceFormat,
@@ -41,7 +44,7 @@ describe('JaegerHttpTraceFormat', () => {
       };
 
       jaegerHttpTraceFormat.inject(
-        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
         carrier
       );
       assert.deepStrictEqual(
@@ -58,7 +61,7 @@ describe('JaegerHttpTraceFormat', () => {
       };
 
       customJaegerHttpTraceFormat.inject(
-        Context.setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
+        setExtractedSpanContext(Context.ROOT_CONTEXT, spanContext),
         carrier
       );
       assert.deepStrictEqual(
@@ -72,7 +75,7 @@ describe('JaegerHttpTraceFormat', () => {
     it('should extract context of a sampled span from carrier', () => {
       carrier[UBER_TRACE_ID_HEADER] =
         'd4cda95b652f4a1592b449d5929fda1b:6e0c63257de34c92:0:01';
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -87,7 +90,7 @@ describe('JaegerHttpTraceFormat', () => {
     it('should extract context of a sampled span from carrier with 1 bit flag', () => {
       carrier[UBER_TRACE_ID_HEADER] =
         '9c41e35aeb6d1272:45fd2a9709dadcf1:a13699e3fb724f40:1';
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -102,7 +105,7 @@ describe('JaegerHttpTraceFormat', () => {
     it('should extract context of a sampled span from UTF-8 encoded carrier', () => {
       carrier[UBER_TRACE_ID_HEADER] =
         'ac1f3dc3c2c0b06e%3A5ac292c4a11a163e%3Ac086aaa825821068%3A1';
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -117,7 +120,7 @@ describe('JaegerHttpTraceFormat', () => {
     it('should use custom header if provided', () => {
       carrier[customHeader] =
         'd4cda95b652f4a1592b449d5929fda1b:6e0c63257de34c92:0:01';
-      const extractedSpanContext = Context.getExtractedSpanContext(
+      const extractedSpanContext = getExtractedSpanContext(
         customJaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
       );
 
@@ -131,7 +134,7 @@ describe('JaegerHttpTraceFormat', () => {
 
     it('returns undefined if UBER_TRACE_ID_HEADER header is missing', () => {
       assert.deepStrictEqual(
-        Context.getExtractedSpanContext(
+        getExtractedSpanContext(
           jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
         ),
         undefined
@@ -141,7 +144,7 @@ describe('JaegerHttpTraceFormat', () => {
     it('returns undefined if UBER_TRACE_ID_HEADER header is invalid', () => {
       carrier[UBER_TRACE_ID_HEADER] = 'invalid!';
       assert.deepStrictEqual(
-        Context.getExtractedSpanContext(
+        getExtractedSpanContext(
           jaegerHttpTraceFormat.extract(Context.ROOT_CONTEXT, carrier)
         ),
         undefined
diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
index aeb809bb1c..d1f944bd5e 100644
--- a/packages/opentelemetry-scope-base/src/context.ts
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -23,8 +23,9 @@ type Store = { [identifer: string]: unknown };
  * but create a new one with updated values.
  */
 export class Context {
-  private _context: Store;
+  private _currentContext: Store;
 
+  /** The root context is used as the default parent context when there is no active context */
   public static readonly ROOT_CONTEXT = new Context();
 
   /**
@@ -32,8 +33,8 @@ export class Context {
    *
    * @param context a context from which to inherit values
    */
-  protected constructor(parentContext: Store = {}) {
-    this._context = Object.assign(Object.create(null), parentContext);
+  private constructor(parentContext: Store = {}) {
+    this._currentContext = Object.assign(Object.create(null), parentContext);
   }
 
   /**
@@ -42,7 +43,7 @@ export class Context {
    * @param key key which identifies a context value
    */
   getValue(key: string): unknown {
-    return this._context[key];
+    return this._currentContext[key];
   }
 
   /**
@@ -53,8 +54,8 @@ export class Context {
    * @param value value to set for the given key
    */
   setValue(key: string, value: unknown): Context {
-    const context = new Context(this._context);
-    context._context[key] = value;
+    const context = new Context(this._currentContext);
+    context._currentContext[key] = value;
     return context;
   }
 
@@ -65,8 +66,8 @@ export class Context {
    * @param key context key for which to clear a value
    */
   deleteValue(key: string): Context {
-    const context = new Context(this._context);
-    delete context._context[key];
+    const context = new Context(this._currentContext);
+    delete context._currentContext[key];
     return context;
   }
 }
diff --git a/packages/opentelemetry-shim-opentracing/src/shim.ts b/packages/opentelemetry-shim-opentracing/src/shim.ts
index 9fa2a0cc9e..c5d09eb8e7 100644
--- a/packages/opentelemetry-shim-opentracing/src/shim.ts
+++ b/packages/opentelemetry-shim-opentracing/src/shim.ts
@@ -15,7 +15,11 @@
  */
 
 import * as types from '@opentelemetry/api';
-import { Context, NoopLogger } from '@opentelemetry/core';
+import {
+  getExtractedSpanContext,
+  NoopLogger,
+  setExtractedSpanContext,
+} from '@opentelemetry/core';
 import * as opentracing from 'opentracing';
 
 function translateReferences(
@@ -131,8 +135,8 @@ export class TracerShim extends opentracing.Tracer {
         this._tracer
           .getHttpTextFormat()
           .inject(
-            Context.setExtractedSpanContext(
-              Context.ROOT_CONTEXT,
+            setExtractedSpanContext(
+              types.Context.ROOT_CONTEXT,
               opentelemSpanContext
             ),
             carrier
@@ -153,10 +157,10 @@ export class TracerShim extends opentracing.Tracer {
       // tslint:disable-next-line:no-switch-case-fall-through
       case opentracing.FORMAT_HTTP_HEADERS:
       case opentracing.FORMAT_TEXT_MAP:
-        const context = Context.getExtractedSpanContext(
+        const context = getExtractedSpanContext(
           this._tracer
             .getHttpTextFormat()
-            .extract(Context.ROOT_CONTEXT, carrier)
+            .extract(types.Context.ROOT_CONTEXT, carrier)
         );
         if (!context) {
           return null;
diff --git a/packages/opentelemetry-tracing/src/Tracer.ts b/packages/opentelemetry-tracing/src/Tracer.ts
index 3cccbfce04..6bff5f84d7 100644
--- a/packages/opentelemetry-tracing/src/Tracer.ts
+++ b/packages/opentelemetry-tracing/src/Tracer.ts
@@ -16,19 +16,20 @@
 
 import * as types from '@opentelemetry/api';
 import {
-  randomTraceId,
+  ConsoleLogger,
+  getActiveSpan,
   isValid,
-  randomSpanId,
   NoRecordingSpan,
-  ConsoleLogger,
-  Context,
+  randomSpanId,
+  randomTraceId,
+  setActiveSpan,
 } from '@opentelemetry/core';
-import { TracerConfig, TraceParams } from './types';
 import { ScopeManager } from '@opentelemetry/scope-base';
+import { BasicTracerProvider } from './BasicTracerProvider';
+import { DEFAULT_CONFIG } from './config';
 import { Span } from './Span';
+import { TraceParams, TracerConfig } from './types';
 import { mergeConfig } from './utility';
-import { DEFAULT_CONFIG } from './config';
-import { BasicTracerProvider } from './BasicTracerProvider';
 
 /**
  * This class represents a basic tracer.
@@ -111,7 +112,7 @@ export class Tracer implements types.Tracer {
    */
   getCurrentSpan(): types.Span | undefined {
     // Get the current Span from the context or null if none found.
-    return Context.getActiveSpan(this._scopeManager.active());
+    return getActiveSpan(this._scopeManager.active());
   }
 
   /**
@@ -123,7 +124,7 @@ export class Tracer implements types.Tracer {
   ): ReturnType<T> {
     // Set given span to context.
     return this._scopeManager.with(
-      Context.setActiveSpan(this._scopeManager.active(), span),
+      setActiveSpan(this._scopeManager.active(), span),
       fn
     );
   }
@@ -135,7 +136,7 @@ export class Tracer implements types.Tracer {
     return this._scopeManager.bind(
       target,
       span
-        ? Context.setActiveSpan(this._scopeManager.active(), span)
+        ? setActiveSpan(this._scopeManager.active(), span)
         : this._scopeManager.active()
     );
   }
diff --git a/packages/opentelemetry-tracing/test/BasicTracerRegistry.test.ts b/packages/opentelemetry-tracing/test/BasicTracerRegistry.test.ts
index 7f8e8047ce..f829de1ff7 100644
--- a/packages/opentelemetry-tracing/test/BasicTracerRegistry.test.ts
+++ b/packages/opentelemetry-tracing/test/BasicTracerRegistry.test.ts
@@ -14,15 +14,15 @@
  * limitations under the License.
  */
 
-import { TraceFlags } from '@opentelemetry/api';
+import { Context, TraceFlags } from '@opentelemetry/api';
 import {
   ALWAYS_SAMPLER,
   BinaryTraceContext,
-  Context,
   HttpTraceContext,
   NEVER_SAMPLER,
   NoopLogger,
   NoRecordingSpan,
+  setActiveSpan,
   TraceState,
 } from '@opentelemetry/core';
 import { NoopScopeManager, ScopeManager } from '@opentelemetry/scope-base';
@@ -317,7 +317,7 @@ describe('BasicTracerProvider', () => {
       const tracer = new BasicTracerProvider({
         scopeManager: {
           active: () =>
-            Context.setActiveSpan(Context.ROOT_CONTEXT, ('foo' as any) as Span),
+            setActiveSpan(Context.ROOT_CONTEXT, ('foo' as any) as Span),
         } as ScopeManager,
       }).getTracer('default');
       assert.deepStrictEqual(tracer.getCurrentSpan(), 'foo');
diff --git a/packages/opentelemetry-web/src/StackScopeManager.ts b/packages/opentelemetry-web/src/StackScopeManager.ts
index 5fe39459e8..72ee4712c6 100644
--- a/packages/opentelemetry-web/src/StackScopeManager.ts
+++ b/packages/opentelemetry-web/src/StackScopeManager.ts
@@ -14,8 +14,8 @@
  * limitations under the License.
  */
 
+import { Context } from '@opentelemetry/api';
 import { ScopeManager } from '@opentelemetry/scope-base';
-import { Context } from '@opentelemetry/core';
 
 /**
  * Stack Scope Manager for managing the state in web
diff --git a/packages/opentelemetry-web/test/StackScopeManager.test.ts b/packages/opentelemetry-web/test/StackScopeManager.test.ts
index 680334a591..3d419aa0cb 100644
--- a/packages/opentelemetry-web/test/StackScopeManager.test.ts
+++ b/packages/opentelemetry-web/test/StackScopeManager.test.ts
@@ -16,7 +16,7 @@
 
 import * as assert from 'assert';
 import { StackScopeManager } from '../src';
-import { Context } from '@opentelemetry/core';
+import { Context } from '@opentelemetry/api';
 
 describe('StackScopeManager', () => {
   let scopeManager: StackScopeManager;

From d89fcc6d1749d095f11b19a2cc1ac9ce63f0533b Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Fri, 7 Feb 2020 13:37:27 -0500
Subject: [PATCH 16/23] chore: remove extra allocation

---
 packages/opentelemetry-scope-base/src/context.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
index d1f944bd5e..4a66b771e8 100644
--- a/packages/opentelemetry-scope-base/src/context.ts
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -33,7 +33,7 @@ export class Context {
    *
    * @param context a context from which to inherit values
    */
-  private constructor(parentContext: Store = {}) {
+  private constructor(parentContext?: Store) {
     this._currentContext = Object.assign(Object.create(null), parentContext);
   }
 

From 68234f742c73367875ddcbed886c3852c3108ba5 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Fri, 7 Feb 2020 13:43:58 -0500
Subject: [PATCH 17/23] chore: review comments

---
 .../opentelemetry-core/test/context/HttpTraceContext.test.ts  | 2 +-
 packages/opentelemetry-plugin-http/src/http.ts                | 4 +++-
 packages/opentelemetry-scope-base/src/context.ts              | 2 +-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts b/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts
index fb53cec343..bc74b8d682 100644
--- a/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts
+++ b/packages/opentelemetry-core/test/context/HttpTraceContext.test.ts
@@ -75,7 +75,7 @@ describe('HttpTraceContext', () => {
     });
   });
 
-  describe('.extract())', () => {
+  describe('.extract()', () => {
     it('should extract context of a sampled span from carrier', () => {
       carrier[TRACE_PARENT_HEADER] =
         '00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01';
diff --git a/packages/opentelemetry-plugin-http/src/http.ts b/packages/opentelemetry-plugin-http/src/http.ts
index 19c9cb7a6f..e72e7a75b3 100644
--- a/packages/opentelemetry-plugin-http/src/http.ts
+++ b/packages/opentelemetry-plugin-http/src/http.ts
@@ -414,11 +414,13 @@ export class HttpPlugin extends BasePlugin<Http> {
       };
 
       const span = plugin._startHttpSpan(operationName, spanOptions);
+
+      if (!options.headers) options.headers = {};
       plugin._tracer
         .getHttpTextFormat()
         // Using context directly like this is temporary. In a future PR, context
         // will be managed by the scope manager (which may be renamed to context manager?)
-        .inject(setActiveSpan(Context.ROOT_CONTEXT, span), options.headers!);
+        .inject(setActiveSpan(Context.ROOT_CONTEXT, span), options.headers);
 
       const request: ClientRequest = plugin._safeExecute(
         span,
diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
index 4a66b771e8..dffebb98e4 100644
--- a/packages/opentelemetry-scope-base/src/context.ts
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -31,7 +31,7 @@ export class Context {
   /**
    * Construct a new context which inherits values from an optional parent context.
    *
-   * @param context a context from which to inherit values
+   * @param parentContext a context from which to inherit values
    */
   private constructor(parentContext?: Store) {
     this._currentContext = Object.assign(Object.create(null), parentContext);

From 2987a5962966abf90e91e3081ad42fc658f0067d Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Wed, 12 Feb 2020 10:13:45 -0500
Subject: [PATCH 18/23] chore: use variables for context keys

---
 .../opentelemetry-core/src/context/context.ts     | 15 ++++++++++-----
 .../test/ZoneScopeManager.test.ts                 |  4 ++--
 .../test/StackScopeManager.test.ts                |  4 ++--
 3 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/packages/opentelemetry-core/src/context/context.ts b/packages/opentelemetry-core/src/context/context.ts
index e1fec8b8b8..ee293556a2 100644
--- a/packages/opentelemetry-core/src/context/context.ts
+++ b/packages/opentelemetry-core/src/context/context.ts
@@ -17,13 +17,16 @@
 import { Span, SpanContext } from '@opentelemetry/api';
 import { Context } from '@opentelemetry/scope-base';
 
+const ACTIVE_SPAN_KEY = 'ACTIVE_SPAN';
+const EXTRACTED_SPAN_CONTEXT_KEY = 'EXTRACTED_SPAN_CONTEXT';
+
 /**
  * Return the active span if one exists
  *
  * @param context context to get span from
  */
 export function getActiveSpan(context: Context): Span | undefined {
-  return (context.getValue('ACTIVE_SPAN') as Span) || undefined;
+  return (context.getValue(ACTIVE_SPAN_KEY) as Span) || undefined;
 }
 
 /**
@@ -33,7 +36,7 @@ export function getActiveSpan(context: Context): Span | undefined {
  * @param span span to set active
  */
 export function setActiveSpan(context: Context, span: Span): Context {
-  return context.setValue('ACTIVE_SPAN', span);
+  return context.setValue(ACTIVE_SPAN_KEY, span);
 }
 
 /**
@@ -45,7 +48,7 @@ export function getExtractedSpanContext(
   context: Context
 ): SpanContext | undefined {
   return (
-    (context.getValue('EXTRACTED_SPAN_CONTEXT') as SpanContext) || undefined
+    (context.getValue(EXTRACTED_SPAN_CONTEXT_KEY) as SpanContext) || undefined
   );
 }
 
@@ -59,7 +62,7 @@ export function setExtractedSpanContext(
   context: Context,
   spanContext: SpanContext
 ): Context {
-  return context.setValue('EXTRACTED_SPAN_CONTEXT', spanContext);
+  return context.setValue(EXTRACTED_SPAN_CONTEXT_KEY, spanContext);
 }
 
 /**
@@ -69,6 +72,8 @@ export function setExtractedSpanContext(
  *
  * @param context context to get values from
  */
-export function getParentSpanContext(context: Context) {
+export function getParentSpanContext(
+  context: Context
+): SpanContext | undefined {
   return getActiveSpan(context)?.context() || getExtractedSpanContext(context);
 }
diff --git a/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts b/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
index 8973c7e06e..57a4694ce2 100644
--- a/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
+++ b/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
@@ -42,7 +42,7 @@ describe('ZoneScopeManager', () => {
       assert.doesNotThrow(() => {
         assert(scopeManager.enable() === scopeManager, 'should return this');
         scopeManager.with(ctx, () => {
-          assert(scopeManager.active() === ctx, 'should has root scope');
+          assert(scopeManager.active() === ctx, 'should have root scope');
         });
       });
     });
@@ -56,7 +56,7 @@ describe('ZoneScopeManager', () => {
         scopeManager.with(ctx, () => {
           assert(
             scopeManager.active() === Context.ROOT_CONTEXT,
-            'should has root scope'
+            'should have root scope'
           );
         });
       });
diff --git a/packages/opentelemetry-web/test/StackScopeManager.test.ts b/packages/opentelemetry-web/test/StackScopeManager.test.ts
index 3d419aa0cb..4e12c9f123 100644
--- a/packages/opentelemetry-web/test/StackScopeManager.test.ts
+++ b/packages/opentelemetry-web/test/StackScopeManager.test.ts
@@ -36,7 +36,7 @@ describe('StackScopeManager', () => {
         assert(scopeManager.enable() === scopeManager, 'should return this');
         assert(
           scopeManager.active() === Context.ROOT_CONTEXT,
-          'should has root scope'
+          'should have root scope'
         );
       });
     });
@@ -48,7 +48,7 @@ describe('StackScopeManager', () => {
         assert(scopeManager.disable() === scopeManager, 'should return this');
         assert(
           scopeManager.active() === Context.ROOT_CONTEXT,
-          'should has no scope'
+          'should have no scope'
         );
       });
     });

From 5ad438311fe3df3ed8c8b992de9f4dbc2fdc12e7 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Wed, 12 Feb 2020 15:53:42 -0500
Subject: [PATCH 19/23] chore: use unique symbols to identify context values

---
 .../opentelemetry-core/src/context/context.ts |  4 +-
 .../test/AsyncHooksScopeManager.test.ts       | 25 +++++-----
 .../opentelemetry-scope-base/src/context.ts   | 25 +++++-----
 .../test/NoopScopeManager.test.ts             |  3 +-
 .../test/ZoneScopeManager.test.ts             | 48 ++++++++++---------
 .../test/StackScopeManager.test.ts            | 27 ++++++-----
 6 files changed, 70 insertions(+), 62 deletions(-)

diff --git a/packages/opentelemetry-core/src/context/context.ts b/packages/opentelemetry-core/src/context/context.ts
index ee293556a2..4ffb649cef 100644
--- a/packages/opentelemetry-core/src/context/context.ts
+++ b/packages/opentelemetry-core/src/context/context.ts
@@ -17,8 +17,8 @@
 import { Span, SpanContext } from '@opentelemetry/api';
 import { Context } from '@opentelemetry/scope-base';
 
-const ACTIVE_SPAN_KEY = 'ACTIVE_SPAN';
-const EXTRACTED_SPAN_CONTEXT_KEY = 'EXTRACTED_SPAN_CONTEXT';
+const ACTIVE_SPAN_KEY = Context.getKey('OpenTelemetry Context Key ACTIVE_SPAN');
+const EXTRACTED_SPAN_CONTEXT_KEY = Context.getKey('OpenTelemetry Context Key EXTRACTED_SPAN_CONTEXT');
 
 /**
  * Return the active span if one exists
diff --git a/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts b/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts
index 6927810b6e..dff24c7774 100644
--- a/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts
+++ b/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts
@@ -21,6 +21,7 @@ import { Context } from '@opentelemetry/scope-base';
 
 describe('AsyncHooksScopeManager', () => {
   let scopeManager: AsyncHooksScopeManager;
+  const key1 = Context.getKey('test key 1');
 
   beforeEach(() => {
     scopeManager = new AsyncHooksScopeManager();
@@ -55,7 +56,7 @@ describe('AsyncHooksScopeManager', () => {
     });
 
     it('should run the callback (object as target)', done => {
-      const test = Context.ROOT_CONTEXT.setValue('a', 1);
+      const test = Context.ROOT_CONTEXT.setValue(key1, 1);
       scopeManager.with(test, () => {
         assert.strictEqual(scopeManager.active(), test, 'should have scope');
         return done();
@@ -80,8 +81,8 @@ describe('AsyncHooksScopeManager', () => {
     });
 
     it('should finally restore an old scope', done => {
-      const scope1 = Context.ROOT_CONTEXT.setValue('name', 'scope1');
-      const scope2 = Context.ROOT_CONTEXT.setValue('name', 'scope2');
+      const scope1 = Context.ROOT_CONTEXT.setValue(key1, 'scope1');
+      const scope2 = Context.ROOT_CONTEXT.setValue(key1, 'scope2');
       scopeManager.with(scope1, () => {
         assert.strictEqual(scopeManager.active(), scope1);
         scopeManager.with(scope2, () => {
@@ -113,7 +114,7 @@ describe('AsyncHooksScopeManager', () => {
     });
 
     it('should return current scope (when enabled)', done => {
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const fn = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();
@@ -127,7 +128,7 @@ describe('AsyncHooksScopeManager', () => {
      */
     it('should return current scope (when disabled)', done => {
       scopeManager.disable();
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const fn = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();
@@ -137,7 +138,7 @@ describe('AsyncHooksScopeManager', () => {
 
     it('should fail to return current scope (when disabled + async op)', done => {
       scopeManager.disable();
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const fn = scopeManager.bind(() => {
         setTimeout(() => {
           assert.strictEqual(
@@ -153,7 +154,7 @@ describe('AsyncHooksScopeManager', () => {
 
     it('should return current scope (when re-enabled + async op)', done => {
       scopeManager.enable();
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const fn = scopeManager.bind(() => {
         setTimeout(() => {
           assert.strictEqual(scopeManager.active(), scope, 'should have scope');
@@ -179,7 +180,7 @@ describe('AsyncHooksScopeManager', () => {
 
     it('should return current scope and removeListener (when enabled)', done => {
       const ee = new EventEmitter();
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         assert.deepStrictEqual(scopeManager.active(), scope);
@@ -194,7 +195,7 @@ describe('AsyncHooksScopeManager', () => {
 
     it('should return current scope and removeAllListener (when enabled)', done => {
       const ee = new EventEmitter();
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         assert.deepStrictEqual(scopeManager.active(), scope);
@@ -214,7 +215,7 @@ describe('AsyncHooksScopeManager', () => {
     it('should return scope (when disabled)', done => {
       scopeManager.disable();
       const ee = new EventEmitter();
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         assert.deepStrictEqual(scopeManager.active(), scope);
@@ -231,7 +232,7 @@ describe('AsyncHooksScopeManager', () => {
     it('should not return current scope (when disabled + async op)', done => {
       scopeManager.disable();
       const ee = new EventEmitter();
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         setImmediate(() => {
@@ -249,7 +250,7 @@ describe('AsyncHooksScopeManager', () => {
     it('should return current scope (when enabled + async op)', done => {
       scopeManager.enable();
       const ee = new EventEmitter();
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const patchedEe = scopeManager.bind(ee, scope);
       const handler = () => {
         setImmediate(() => {
diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
index dffebb98e4..67443d5bff 100644
--- a/packages/opentelemetry-scope-base/src/context.ts
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -14,8 +14,6 @@
  * limitations under the License.
  */
 
-/** Map of identifiers to an unknown value used internally to store context */
-type Store = { [identifer: string]: unknown };
 
 /**
  * Class which stores and manages current context values. All methods which
@@ -23,18 +21,23 @@ type Store = { [identifer: string]: unknown };
  * but create a new one with updated values.
  */
 export class Context {
-  private _currentContext: Store;
+  private _currentContext: Map<symbol, unknown>;
 
   /** The root context is used as the default parent context when there is no active context */
   public static readonly ROOT_CONTEXT = new Context();
 
+  /** Get a key to uniquely identify a context value */
+  public static getKey(description: string) {
+    return Symbol(description);
+  }
+
   /**
    * Construct a new context which inherits values from an optional parent context.
    *
    * @param parentContext a context from which to inherit values
    */
-  private constructor(parentContext?: Store) {
-    this._currentContext = Object.assign(Object.create(null), parentContext);
+  private constructor(parentContext?: Map<symbol, unknown>) {
+    this._currentContext = parentContext ? new Map(parentContext) : new Map();
   }
 
   /**
@@ -42,8 +45,8 @@ export class Context {
    *
    * @param key key which identifies a context value
    */
-  getValue(key: string): unknown {
-    return this._currentContext[key];
+  getValue(key: symbol): unknown {
+    return this._currentContext.get(key);
   }
 
   /**
@@ -53,9 +56,9 @@ export class Context {
    * @param key context key for which to set the value
    * @param value value to set for the given key
    */
-  setValue(key: string, value: unknown): Context {
+  setValue(key: symbol, value: unknown): Context {
     const context = new Context(this._currentContext);
-    context._currentContext[key] = value;
+    context._currentContext.set(key, value);
     return context;
   }
 
@@ -65,9 +68,9 @@ export class Context {
    *
    * @param key context key for which to clear a value
    */
-  deleteValue(key: string): Context {
+  deleteValue(key: symbol): Context {
     const context = new Context(this._currentContext);
-    delete context._currentContext[key];
+    context._currentContext.delete(key);
     return context;
   }
 }
diff --git a/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts b/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts
index 5a9245b666..0e68a4be79 100644
--- a/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts
+++ b/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts
@@ -44,7 +44,8 @@ describe('NoopScopeManager', () => {
     });
 
     it('should run the callback (object as target)', done => {
-      const test = Context.ROOT_CONTEXT.setValue('a', 1);
+      const key = Context.getKey('test key 1');
+      const test = Context.ROOT_CONTEXT.setValue(key, 1);
       scopeManager.with(test, () => {
         assert.strictEqual(
           scopeManager.active(),
diff --git a/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts b/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
index 57a4694ce2..bed361e41a 100644
--- a/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
+++ b/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
@@ -24,6 +24,8 @@ let clock: any;
 
 describe('ZoneScopeManager', () => {
   let scopeManager: ZoneScopeManager;
+  const key1 = Context.getKey('test key 1');
+  const key2 = Context.getKey('test key 2');
 
   beforeEach(() => {
     clock = sinon.useFakeTimers();
@@ -38,7 +40,7 @@ describe('ZoneScopeManager', () => {
 
   describe('.enable()', () => {
     it('should work', () => {
-      const ctx = Context.ROOT_CONTEXT.setValue('a', 1);
+      const ctx = Context.ROOT_CONTEXT.setValue(key1, 1);
       assert.doesNotThrow(() => {
         assert(scopeManager.enable() === scopeManager, 'should return this');
         scopeManager.with(ctx, () => {
@@ -50,7 +52,7 @@ describe('ZoneScopeManager', () => {
 
   describe('.disable()', () => {
     it('should work', () => {
-      const ctx = Context.ROOT_CONTEXT.setValue('a', 1);
+      const ctx = Context.ROOT_CONTEXT.setValue(key1, 1);
       assert.doesNotThrow(() => {
         assert(scopeManager.disable() === scopeManager, 'should return this');
         scopeManager.with(ctx, () => {
@@ -69,7 +71,7 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should run the callback (object as target)', done => {
-      const test = Context.ROOT_CONTEXT.setValue('a', 1);
+      const test = Context.ROOT_CONTEXT.setValue(key1, 1);
       scopeManager.with(test, () => {
         assert.strictEqual(scopeManager.active(), test, 'should have scope');
         return done();
@@ -94,9 +96,9 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should finally restore an old scope, including the async task', done => {
-      const scope1 = Context.ROOT_CONTEXT.setValue('scope', 'scope1');
-      const scope2 = Context.ROOT_CONTEXT.setValue('scope', 'scope2');
-      const scope3 = Context.ROOT_CONTEXT.setValue('scope', 'scope3');
+      const scope1 = Context.ROOT_CONTEXT.setValue(key1, 'scope1');
+      const scope2 = Context.ROOT_CONTEXT.setValue(key1, 'scope2');
+      const scope3 = Context.ROOT_CONTEXT.setValue(key1, 'scope3');
 
       scopeManager.with(scope1, () => {
         assert.strictEqual(scopeManager.active(), scope1);
@@ -118,9 +120,9 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should finally restore an old scope when scope is an object, including the async task', done => {
-      const scope1 = Context.ROOT_CONTEXT.setValue('x', 1);
-      const scope2 = Context.ROOT_CONTEXT.setValue('x', 2);
-      const scope3 = Context.ROOT_CONTEXT.setValue('x', 3);
+      const scope1 = Context.ROOT_CONTEXT.setValue(key1, 1);
+      const scope2 = Context.ROOT_CONTEXT.setValue(key1, 2);
+      const scope3 = Context.ROOT_CONTEXT.setValue(key1, 3);
       scopeManager.with(scope1, () => {
         assert.strictEqual(scopeManager.active(), scope1);
         scopeManager.with(scope2, () => {
@@ -140,29 +142,29 @@ describe('ZoneScopeManager', () => {
       assert.strictEqual(scopeManager.active(), window);
     });
     it('should correctly return the scopes for 3 parallel actions', () => {
-      const rootSpan = Context.ROOT_CONTEXT.setValue('name', 'root');
+      const rootSpan = Context.ROOT_CONTEXT.setValue(key1, 'root');
       scopeManager.with(rootSpan, () => {
         assert.ok(
-          scopeManager.active().getValue('name') === 'root',
+          scopeManager.active().getValue(key1) === 'root',
           'Current span is rootSpan'
         );
         const concurrentSpan1 = Context.ROOT_CONTEXT.setValue(
-          'span',
+          key2,
           'concurrentSpan1'
         );
         const concurrentSpan2 = Context.ROOT_CONTEXT.setValue(
-          'span',
+          key2,
           'concurrentSpan2'
         );
         const concurrentSpan3 = Context.ROOT_CONTEXT.setValue(
-          'span',
+          key2,
           'concurrentSpan3'
         );
 
         scopeManager.with(concurrentSpan1, () => {
           setTimeout(() => {
             assert.ok(
-              scopeManager.active().getValue('span') === concurrentSpan1,
+              scopeManager.active().getValue(key2) === concurrentSpan1,
               'Current span is concurrentSpan1'
             );
           }, 10);
@@ -171,7 +173,7 @@ describe('ZoneScopeManager', () => {
         scopeManager.with(concurrentSpan2, () => {
           setTimeout(() => {
             assert.ok(
-              scopeManager.active().getValue('span') === concurrentSpan2,
+              scopeManager.active().getValue(key2) === concurrentSpan2,
               'Current span is concurrentSpan2'
             );
           }, 20);
@@ -180,7 +182,7 @@ describe('ZoneScopeManager', () => {
         scopeManager.with(concurrentSpan3, () => {
           setTimeout(() => {
             assert.ok(
-              scopeManager.active().getValue('span') === concurrentSpan3,
+              scopeManager.active().getValue(key2) === concurrentSpan3,
               'Current span is concurrentSpan3'
             );
           }, 30);
@@ -199,12 +201,12 @@ describe('ZoneScopeManager', () => {
         }
 
         getTitle() {
-          return (scopeManager.active().getValue('obj') as Obj).title;
+          return (scopeManager.active().getValue(key1) as Obj).title;
         }
       }
 
       const obj1 = new Obj('a1');
-      const ctx = Context.ROOT_CONTEXT.setValue('obj', obj1);
+      const ctx = Context.ROOT_CONTEXT.setValue(key1, obj1);
       obj1.title = 'a2';
       const obj2 = new Obj('b1');
       const wrapper: any = scopeManager.bind(obj2.getTitle, ctx);
@@ -230,7 +232,7 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should return current scope (when enabled)', done => {
-      const scope = Context.ROOT_CONTEXT.setValue('ctx', { a: 1 });
+      const scope = Context.ROOT_CONTEXT.setValue(key1, { a: 1 });
       const fn: any = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();
@@ -240,7 +242,7 @@ describe('ZoneScopeManager', () => {
 
     it('should return root scope (when disabled)', done => {
       scopeManager.disable();
-      const scope = Context.ROOT_CONTEXT.setValue('ctx', { a: 1 });
+      const scope = Context.ROOT_CONTEXT.setValue(key1, { a: 1 });
       const fn: any = scopeManager.bind(() => {
         assert.strictEqual(
           scopeManager.active(),
@@ -253,7 +255,7 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should bind the the certain scope to the target "addEventListener" function', done => {
-      const scope1 = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope1 = Context.ROOT_CONTEXT.setValue(key1, 1);
       const element = document.createElement('div');
 
       scopeManager.bind(element, scope1);
@@ -277,7 +279,7 @@ describe('ZoneScopeManager', () => {
     });
 
     it('should preserve zone when creating new click event inside zone', done => {
-      const scope1 = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope1 = Context.ROOT_CONTEXT.setValue(key1, 1);
       const element = document.createElement('div');
 
       scopeManager.bind(element, scope1);
diff --git a/packages/opentelemetry-web/test/StackScopeManager.test.ts b/packages/opentelemetry-web/test/StackScopeManager.test.ts
index 4e12c9f123..0f33e996ba 100644
--- a/packages/opentelemetry-web/test/StackScopeManager.test.ts
+++ b/packages/opentelemetry-web/test/StackScopeManager.test.ts
@@ -20,6 +20,7 @@ import { Context } from '@opentelemetry/api';
 
 describe('StackScopeManager', () => {
   let scopeManager: StackScopeManager;
+  const key1 = Context.getKey('test key 1');
 
   beforeEach(() => {
     scopeManager = new StackScopeManager();
@@ -60,7 +61,7 @@ describe('StackScopeManager', () => {
     });
 
     it('should run the callback (object as target)', done => {
-      const test = Context.ROOT_CONTEXT.setValue('a', 1);
+      const test = Context.ROOT_CONTEXT.setValue(key1, 1);
       scopeManager.with(test, () => {
         assert.strictEqual(scopeManager.active(), test, 'should have scope');
         return done();
@@ -85,9 +86,9 @@ describe('StackScopeManager', () => {
     });
 
     it('should finally restore an old scope', done => {
-      const scope1 = Context.ROOT_CONTEXT.setValue('name', 'scope1');
-      const scope2 = Context.ROOT_CONTEXT.setValue('name', 'scope2');
-      const scope3 = Context.ROOT_CONTEXT.setValue('name', 'scope3');
+      const scope1 = Context.ROOT_CONTEXT.setValue(key1, 'scope1');
+      const scope2 = Context.ROOT_CONTEXT.setValue(key1, 'scope2');
+      const scope3 = Context.ROOT_CONTEXT.setValue(key1, 'scope3');
       scopeManager.with(scope1, () => {
         assert.strictEqual(scopeManager.active(), scope1);
         scopeManager.with(scope2, () => {
@@ -104,9 +105,9 @@ describe('StackScopeManager', () => {
     });
 
     it('should finally restore an old scope when scope is an object', done => {
-      const scope1 = Context.ROOT_CONTEXT.setValue('a', 1);
-      const scope2 = Context.ROOT_CONTEXT.setValue('a', 2);
-      const scope3 = Context.ROOT_CONTEXT.setValue('a', 3);
+      const scope1 = Context.ROOT_CONTEXT.setValue(key1, 1);
+      const scope2 = Context.ROOT_CONTEXT.setValue(key1, 2);
+      const scope3 = Context.ROOT_CONTEXT.setValue(key1, 3);
       scopeManager.with(scope1, () => {
         assert.strictEqual(scopeManager.active(), scope1);
         scopeManager.with(scope2, () => {
@@ -133,12 +134,12 @@ describe('StackScopeManager', () => {
         }
 
         getTitle() {
-          return (scopeManager.active().getValue('obj') as Obj).title;
+          return (scopeManager.active().getValue(key1) as Obj).title;
         }
       }
 
       const obj1 = new Obj('a1');
-      const ctx = Context.ROOT_CONTEXT.setValue('obj', obj1);
+      const ctx = Context.ROOT_CONTEXT.setValue(key1, obj1);
       obj1.title = 'a2';
       const obj2 = new Obj('b1');
       const wrapper: any = scopeManager.bind(obj2.getTitle, ctx);
@@ -146,19 +147,19 @@ describe('StackScopeManager', () => {
     });
 
     it('should return the same target (when enabled)', () => {
-      const test = Context.ROOT_CONTEXT.setValue('a', 1);
+      const test = Context.ROOT_CONTEXT.setValue(key1, 1);
       assert.deepStrictEqual(scopeManager.bind(test), test);
     });
 
     it('should return the same target (when disabled)', () => {
       scopeManager.disable();
-      const test = Context.ROOT_CONTEXT.setValue('a', 1);
+      const test = Context.ROOT_CONTEXT.setValue(key1, 1);
       assert.deepStrictEqual(scopeManager.bind(test), test);
       scopeManager.enable();
     });
 
     it('should return current scope (when enabled)', done => {
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const fn: any = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();
@@ -168,7 +169,7 @@ describe('StackScopeManager', () => {
 
     it('should return current scope (when disabled)', done => {
       scopeManager.disable();
-      const scope = Context.ROOT_CONTEXT.setValue('a', 1);
+      const scope = Context.ROOT_CONTEXT.setValue(key1, 1);
       const fn: any = scopeManager.bind(() => {
         assert.strictEqual(scopeManager.active(), scope, 'should have scope');
         return done();

From d5ef1d8b896ad3e02033db60ad777a35c53a19ff Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Wed, 12 Feb 2020 16:06:38 -0500
Subject: [PATCH 20/23] chore: use TODO context reference

---
 packages/opentelemetry-plugin-http/src/http.ts           | 4 ++--
 .../opentelemetry-plugin-xml-http-request/src/xhr.ts     | 2 +-
 packages/opentelemetry-scope-base/src/context.ts         | 9 +++++++++
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/packages/opentelemetry-plugin-http/src/http.ts b/packages/opentelemetry-plugin-http/src/http.ts
index e72e7a75b3..d11b4b0708 100644
--- a/packages/opentelemetry-plugin-http/src/http.ts
+++ b/packages/opentelemetry-plugin-http/src/http.ts
@@ -306,7 +306,7 @@ export class HttpPlugin extends BasePlugin<Http> {
       // Using context directly like this is temporary. In a future PR, context
       // will be managed by the scope manager (which may be renamed to context manager?)
       const spanContext = getExtractedSpanContext(
-        propagation.extract(Context.ROOT_CONTEXT, headers)
+        propagation.extract(Context.TODO, headers)
       );
       if (spanContext && isValid(spanContext)) {
         spanOptions.parent = spanContext;
@@ -420,7 +420,7 @@ export class HttpPlugin extends BasePlugin<Http> {
         .getHttpTextFormat()
         // Using context directly like this is temporary. In a future PR, context
         // will be managed by the scope manager (which may be renamed to context manager?)
-        .inject(setActiveSpan(Context.ROOT_CONTEXT, span), options.headers);
+        .inject(setActiveSpan(Context.TODO, span), options.headers);
 
       const request: ClientRequest = plugin._safeExecute(
         span,
diff --git a/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts b/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
index 8aea846312..cef6eff144 100644
--- a/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
+++ b/packages/opentelemetry-plugin-xml-http-request/src/xhr.ts
@@ -92,7 +92,7 @@ export class XMLHttpRequestPlugin extends BasePlugin<XMLHttpRequest> {
       .getHttpTextFormat()
       // Using context direclty like this is temporary. In a future PR, context
       // will be managed by the scope manager (which may be renamed to context manager?)
-      .inject(setActiveSpan(types.Context.ROOT_CONTEXT, span), headers);
+      .inject(setActiveSpan(types.Context.TODO, span), headers);
 
     Object.keys(headers).forEach(key => {
       xhr.setRequestHeader(key, String(headers[key]));
diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
index 67443d5bff..491f863264 100644
--- a/packages/opentelemetry-scope-base/src/context.ts
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -26,6 +26,15 @@ export class Context {
   /** The root context is used as the default parent context when there is no active context */
   public static readonly ROOT_CONTEXT = new Context();
 
+
+  /** 
+   * This is another identifier to the root context which allows developers to easily search the
+   * codebase for direct uses of context which need to be removed in later PRs.
+   * 
+   * It's existence is temporary and it should be removed when all references are fixed.
+   */
+  public static readonly TODO = Context.ROOT_CONTEXT;
+
   /** Get a key to uniquely identify a context value */
   public static getKey(description: string) {
     return Symbol(description);

From e750d4b67415a7f074492d4a772bb225f21fb16d Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Wed, 12 Feb 2020 16:06:50 -0500
Subject: [PATCH 21/23] chore: remove root context from dummy propagator

---
 .../opentelemetry-plugin-http/test/utils/DummyPropagation.ts    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts b/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts
index 887b7127a0..5c65bd16d7 100644
--- a/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts
+++ b/packages/opentelemetry-plugin-http/test/utils/DummyPropagation.ts
@@ -24,7 +24,7 @@ export class DummyPropagation implements HttpTextFormat {
   static TRACE_CONTEXT_KEY = 'x-dummy-trace-id';
   static SPAN_CONTEXT_KEY = 'x-dummy-span-id';
   extract(context: Context, carrier: http.OutgoingHttpHeaders) {
-    return setExtractedSpanContext(Context.ROOT_CONTEXT, {
+    return setExtractedSpanContext(context, {
       traceId: carrier[DummyPropagation.TRACE_CONTEXT_KEY] as string,
       spanId: DummyPropagation.SPAN_CONTEXT_KEY,
     });

From adff03cb64f931f5a282cb52e115262196fc58f4 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Wed, 12 Feb 2020 16:09:50 -0500
Subject: [PATCH 22/23] chore: lint

---
 packages/opentelemetry-core/src/context/context.ts | 4 +++-
 packages/opentelemetry-scope-base/src/context.ts   | 6 ++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/packages/opentelemetry-core/src/context/context.ts b/packages/opentelemetry-core/src/context/context.ts
index 4ffb649cef..16f430f13f 100644
--- a/packages/opentelemetry-core/src/context/context.ts
+++ b/packages/opentelemetry-core/src/context/context.ts
@@ -18,7 +18,9 @@ import { Span, SpanContext } from '@opentelemetry/api';
 import { Context } from '@opentelemetry/scope-base';
 
 const ACTIVE_SPAN_KEY = Context.getKey('OpenTelemetry Context Key ACTIVE_SPAN');
-const EXTRACTED_SPAN_CONTEXT_KEY = Context.getKey('OpenTelemetry Context Key EXTRACTED_SPAN_CONTEXT');
+const EXTRACTED_SPAN_CONTEXT_KEY = Context.getKey(
+  'OpenTelemetry Context Key EXTRACTED_SPAN_CONTEXT'
+);
 
 /**
  * Return the active span if one exists
diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
index 491f863264..23dcf84dd2 100644
--- a/packages/opentelemetry-scope-base/src/context.ts
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -14,7 +14,6 @@
  * limitations under the License.
  */
 
-
 /**
  * Class which stores and manages current context values. All methods which
  * update context such as get and delete do not modify an existing context,
@@ -26,11 +25,10 @@ export class Context {
   /** The root context is used as the default parent context when there is no active context */
   public static readonly ROOT_CONTEXT = new Context();
 
-
-  /** 
+  /**
    * This is another identifier to the root context which allows developers to easily search the
    * codebase for direct uses of context which need to be removed in later PRs.
-   * 
+   *
    * It's existence is temporary and it should be removed when all references are fixed.
    */
   public static readonly TODO = Context.ROOT_CONTEXT;

From 8e433f17a6d7a772a55fe57d72f143ca0b43f085 Mon Sep 17 00:00:00 2001
From: Daniel Dyla <dyladan@users.noreply.github.com>
Date: Wed, 12 Feb 2020 16:36:10 -0500
Subject: [PATCH 23/23] chore: rename getKey to createKey

---
 packages/opentelemetry-core/src/context/context.ts          | 6 ++++--
 .../test/AsyncHooksScopeManager.test.ts                     | 2 +-
 packages/opentelemetry-scope-base/src/context.ts            | 2 +-
 .../opentelemetry-scope-base/test/NoopScopeManager.test.ts  | 2 +-
 .../test/ZoneScopeManager.test.ts                           | 4 ++--
 packages/opentelemetry-web/test/StackScopeManager.test.ts   | 2 +-
 6 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/packages/opentelemetry-core/src/context/context.ts b/packages/opentelemetry-core/src/context/context.ts
index 16f430f13f..0ae080b3ed 100644
--- a/packages/opentelemetry-core/src/context/context.ts
+++ b/packages/opentelemetry-core/src/context/context.ts
@@ -17,8 +17,10 @@
 import { Span, SpanContext } from '@opentelemetry/api';
 import { Context } from '@opentelemetry/scope-base';
 
-const ACTIVE_SPAN_KEY = Context.getKey('OpenTelemetry Context Key ACTIVE_SPAN');
-const EXTRACTED_SPAN_CONTEXT_KEY = Context.getKey(
+const ACTIVE_SPAN_KEY = Context.createKey(
+  'OpenTelemetry Context Key ACTIVE_SPAN'
+);
+const EXTRACTED_SPAN_CONTEXT_KEY = Context.createKey(
   'OpenTelemetry Context Key EXTRACTED_SPAN_CONTEXT'
 );
 
diff --git a/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts b/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts
index dff24c7774..ea85caf6a3 100644
--- a/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts
+++ b/packages/opentelemetry-scope-async-hooks/test/AsyncHooksScopeManager.test.ts
@@ -21,7 +21,7 @@ import { Context } from '@opentelemetry/scope-base';
 
 describe('AsyncHooksScopeManager', () => {
   let scopeManager: AsyncHooksScopeManager;
-  const key1 = Context.getKey('test key 1');
+  const key1 = Context.createKey('test key 1');
 
   beforeEach(() => {
     scopeManager = new AsyncHooksScopeManager();
diff --git a/packages/opentelemetry-scope-base/src/context.ts b/packages/opentelemetry-scope-base/src/context.ts
index 23dcf84dd2..8b42d7e9af 100644
--- a/packages/opentelemetry-scope-base/src/context.ts
+++ b/packages/opentelemetry-scope-base/src/context.ts
@@ -34,7 +34,7 @@ export class Context {
   public static readonly TODO = Context.ROOT_CONTEXT;
 
   /** Get a key to uniquely identify a context value */
-  public static getKey(description: string) {
+  public static createKey(description: string) {
     return Symbol(description);
   }
 
diff --git a/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts b/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts
index 0e68a4be79..8daf15ded0 100644
--- a/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts
+++ b/packages/opentelemetry-scope-base/test/NoopScopeManager.test.ts
@@ -44,7 +44,7 @@ describe('NoopScopeManager', () => {
     });
 
     it('should run the callback (object as target)', done => {
-      const key = Context.getKey('test key 1');
+      const key = Context.createKey('test key 1');
       const test = Context.ROOT_CONTEXT.setValue(key, 1);
       scopeManager.with(test, () => {
         assert.strictEqual(
diff --git a/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts b/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
index bed361e41a..33e62c29e6 100644
--- a/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
+++ b/packages/opentelemetry-scope-zone-peer-dep/test/ZoneScopeManager.test.ts
@@ -24,8 +24,8 @@ let clock: any;
 
 describe('ZoneScopeManager', () => {
   let scopeManager: ZoneScopeManager;
-  const key1 = Context.getKey('test key 1');
-  const key2 = Context.getKey('test key 2');
+  const key1 = Context.createKey('test key 1');
+  const key2 = Context.createKey('test key 2');
 
   beforeEach(() => {
     clock = sinon.useFakeTimers();
diff --git a/packages/opentelemetry-web/test/StackScopeManager.test.ts b/packages/opentelemetry-web/test/StackScopeManager.test.ts
index 0f33e996ba..bb0e92970d 100644
--- a/packages/opentelemetry-web/test/StackScopeManager.test.ts
+++ b/packages/opentelemetry-web/test/StackScopeManager.test.ts
@@ -20,7 +20,7 @@ import { Context } from '@opentelemetry/api';
 
 describe('StackScopeManager', () => {
   let scopeManager: StackScopeManager;
-  const key1 = Context.getKey('test key 1');
+  const key1 = Context.createKey('test key 1');
 
   beforeEach(() => {
     scopeManager = new StackScopeManager();