Move global tracer and substitute agent-core types with API types where this is trivially possible.

CHANGELOG.asciidoc

@@ -19,7 +19,6 @@ endif::[]
 ////
 
 === Unreleased
-* Introduce *apm-agent-tracer* module that contains a minimal, zero-dependency `Tracer` API. - {pull}3043[#3043]
 
 [[release-notes-1.37.0]]
 ==== 1.37.0 - YYYY/MM/DD

apm-agent-core/src/main/java/co/elastic/apm/agent/bci/ElasticApmAgent.java

@@ -36,7 +36,8 @@
 import co.elastic.apm.agent.configuration.CoreConfiguration;
 import co.elastic.apm.agent.impl.ElasticApmTracer;
 import co.elastic.apm.agent.impl.ElasticApmTracerBuilder;
-import co.elastic.apm.agent.impl.GlobalTracer;
+import co.elastic.apm.agent.impl.Tracer;
+import co.elastic.apm.agent.tracer.GlobalTracer;
 import co.elastic.apm.agent.logging.ApmServerLogAppender;
 import co.elastic.apm.agent.matcher.MethodMatcher;
 import co.elastic.apm.agent.sdk.ElasticApmInstrumentation;
@@ -179,7 +180,7 @@ private static void initInstrumentation(ElasticApmTracer tracer, Instrumentation
     }
 
     @Nonnull
-    private static Iterable<ElasticApmInstrumentation> loadInstrumentations(ElasticApmTracer tracer) {
+    private static Iterable<ElasticApmInstrumentation> loadInstrumentations(Tracer tracer) {
         List<ClassLoader> pluginClassLoaders = new ArrayList<>();
         pluginClassLoaders.add(PrivilegedActionUtils.getClassLoader(ElasticApmAgent.class));
         pluginClassLoaders.addAll(createExternalPluginClassLoaders(tracer.getConfig(CoreConfiguration.class).getPluginsDir()));
@@ -308,7 +309,7 @@ public void onChange(ConfigurationOption configurationOption, Object oldValue, O
     }
 
     public static synchronized Future<?> reInitInstrumentation() {
-        final ElasticApmTracer tracer = GlobalTracer.requireTracerImpl();
+        final Tracer tracer = TracerAwareInstrumentation.tracer.require(Tracer.class);
         if (instrumentation == null) {
             throw new IllegalStateException("Can't re-init agent before it has been initialized");
         }
@@ -340,7 +341,7 @@ public static boolean openModule(Class<?> classFromTargetModule, ClassLoader ope
     static synchronized void doReInitInstrumentation(Iterable<ElasticApmInstrumentation> instrumentations) {
         Logger logger = getLogger();
         logger.info("Re initializing instrumentation");
-        AgentBuilder agentBuilder = initAgentBuilder(GlobalTracer.requireTracerImpl(), instrumentation, instrumentations, logger, AgentBuilder.DescriptionStrategy.Default.POOL_ONLY, false);
+        AgentBuilder agentBuilder = initAgentBuilder(GlobalTracer.get().require(ElasticApmTracer.class), instrumentation, instrumentations, logger, AgentBuilder.DescriptionStrategy.Default.POOL_ONLY, false);
 
         resettableClassFileTransformer = agentBuilder.patchOn(instrumentation, resettableClassFileTransformer);
     }
@@ -457,7 +458,7 @@ public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder, TypeDesc
     private static Logger getLogger() {
         if (logger == null) {
             // lazily init logger to allow the tracer builder to init the logging config first
-            GlobalTracer.requireTracerImpl();
+            GlobalTracer.get().require(ElasticApmTracer.class);
             logger = LoggerFactory.getLogger(ElasticApmAgent.class);
         }
         // re-using an existing logger avoids running into a JVM bug that leads to a segfault
@@ -646,7 +647,7 @@ public static synchronized void reset() {
         if (instrumentation == null) {
             return;
         }
-        GlobalTracer.get().stop();
+        GlobalTracer.get().require(Tracer.class).stop();
         GlobalTracer.setNoop();
         Exception exception = null;
         if (resettableClassFileTransformer != null) {
@@ -788,7 +789,7 @@ public static void ensureInstrumented(final Class<?> classToInstrument,
 
         if (!appliedInstrumentations.contains(instrumentationClasses)) {
             synchronized (ElasticApmAgent.class) {
-                final ElasticApmTracer tracer = GlobalTracer.requireTracerImpl();
+                final ElasticApmTracer tracer = GlobalTracer.get().require(ElasticApmTracer.class);
                 if (instrumentation == null) {
                     throw new IllegalStateException("Agent is not initialized");
                 }
@@ -896,7 +897,11 @@ private static ElasticApmInstrumentation tryInstantiate(Class<? extends ElasticA
         Constructor<? extends ElasticApmInstrumentation> constructor = null;
         try {
             if (withTracer) {
-                constructor = instrumentation.getConstructor(ElasticApmTracer.class);
+                try {
+                    constructor = instrumentation.getConstructor(ElasticApmTracer.class);
+                } catch (NoSuchMethodException ignored) {
+                    constructor = instrumentation.getConstructor(co.elastic.apm.agent.tracer.Tracer.class);
+                }
             } else {
                 constructor = instrumentation.getConstructor();
             }
@@ -908,7 +913,7 @@ private static ElasticApmInstrumentation tryInstantiate(Class<? extends ElasticA
         if (constructor != null) {
             try {
                 if (withTracer) {
-                    instance = constructor.newInstance(GlobalTracer.requireTracerImpl());
+                    instance = constructor.newInstance(GlobalTracer.get().require(ElasticApmTracer.class));
                 } else {
                     instance = constructor.newInstance();
                 }

apm-agent-core/src/main/java/co/elastic/apm/agent/bci/TracerAwareInstrumentation.java

@@ -18,13 +18,12 @@
  */
 package co.elastic.apm.agent.bci;
 
-import co.elastic.apm.agent.impl.ElasticApmTracer;
-import co.elastic.apm.agent.impl.GlobalTracer;
-import co.elastic.apm.agent.impl.Tracer;
+import co.elastic.apm.agent.tracer.GlobalTracer;
 import co.elastic.apm.agent.sdk.ElasticApmInstrumentation;
+import co.elastic.apm.agent.tracer.Tracer;
 
 /**
- * The constructor can optionally have a {@link ElasticApmTracer} parameter.
+ * The constructor can optionally have a {@link Tracer} parameter.
  */
 public abstract class TracerAwareInstrumentation extends ElasticApmInstrumentation {
 

apm-agent-core/src/main/java/co/elastic/apm/agent/collections/SpanConcurrentHashMap.java

@@ -18,7 +18,7 @@
  */
 package co.elastic.apm.agent.collections;
 
-import co.elastic.apm.agent.impl.transaction.AbstractSpan;
+import co.elastic.apm.agent.tracer.AbstractSpan;
 
 import javax.annotation.Nullable;
 import java.util.Iterator;

apm-agent-core/src/main/java/co/elastic/apm/agent/collections/WeakConcurrentProviderImpl.java

@@ -18,11 +18,11 @@
  */
 package co.elastic.apm.agent.collections;
 
-import co.elastic.apm.agent.impl.transaction.AbstractSpan;
 import co.elastic.apm.agent.sdk.weakconcurrent.DetachedThreadLocal;
 import co.elastic.apm.agent.sdk.weakconcurrent.WeakConcurrent;
 import co.elastic.apm.agent.sdk.weakconcurrent.WeakMap;
 import co.elastic.apm.agent.sdk.weakconcurrent.WeakSet;
+import co.elastic.apm.agent.tracer.AbstractSpan;
 import com.blogspot.mydailyjava.weaklockfree.AbstractWeakConcurrentMap;
 import com.blogspot.mydailyjava.weaklockfree.WeakConcurrentSet;
 

apm-agent-core/src/main/java/co/elastic/apm/agent/impl/ElasticApmTracer.java

@@ -46,17 +46,21 @@
 import co.elastic.apm.agent.sdk.logging.LoggerFactory;
 import co.elastic.apm.agent.sdk.weakconcurrent.WeakConcurrent;
 import co.elastic.apm.agent.sdk.weakconcurrent.WeakMap;
+import co.elastic.apm.agent.tracer.GlobalTracer;
 import co.elastic.apm.agent.util.DependencyInjectingServiceLoader;
 import co.elastic.apm.agent.util.ExecutorUtils;
 import co.elastic.apm.agent.tracer.Scope;
 import co.elastic.apm.agent.tracer.dispatch.BinaryHeaderGetter;
 import co.elastic.apm.agent.tracer.dispatch.TextHeaderGetter;
+import co.elastic.apm.agent.util.PrivilegedActionUtils;
+import co.elastic.apm.agent.util.VersionUtils;
 import org.stagemonitor.configuration.ConfigurationOption;
 import org.stagemonitor.configuration.ConfigurationOptionProvider;
 import org.stagemonitor.configuration.ConfigurationRegistry;
 
 import javax.annotation.Nullable;
 import java.io.Closeable;
+import java.io.File;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
@@ -77,6 +81,8 @@ public class ElasticApmTracer implements Tracer {
 
     private static final WeakMap<ClassLoader, ServiceInfo> serviceInfoByClassLoader = WeakConcurrent.buildMap();
 
+    private static volatile boolean classloaderCheckOk = false;
+
     private final ConfigurationRegistry configurationRegistry;
     private final StacktraceConfiguration stacktraceConfiguration;
     private final ApmServerClient apmServerClient;
@@ -117,6 +123,49 @@ protected ActiveStack initialValue() {
     private final String ephemeralId;
     private final MetaDataFuture metaDataFuture;
 
+    static {
+        checkClassloader();
+    }
+
+    private static void checkClassloader() {
+        ClassLoader cl = PrivilegedActionUtils.getClassLoader(GlobalTracer.class);
+
+        // agent currently loaded in the bootstrap CL, which is the current correct location
+        if (cl == null) {
+            return;
+        }
+
+        if (classloaderCheckOk) {
+            return;
+        }
+
+        String agentLocation = PrivilegedActionUtils.getProtectionDomain(GlobalTracer.class).getCodeSource().getLocation().getFile();
+        if (!agentLocation.endsWith(".jar")) {
+            // agent is not packaged, thus we assume running tests
+            classloaderCheckOk = true;
+            return;
+        }
+
+        String premainClass = VersionUtils.getManifestEntry(new File(agentLocation), "Premain-Class");
+        if (null == premainClass) {
+            // packaged within a .jar, but not within an agent jar, thus we assume it's still for testing
+            classloaderCheckOk = true;
+            return;
+        }
+
+        if (premainClass.startsWith("co.elastic.apm.agent")) {
+            // premain class will only be present when packaged as an agent jar
+            classloaderCheckOk = true;
+            return;
+        }
+
+        // A packaged agent class has been loaded outside of bootstrap classloader, we are not in the context of
+        // unit/integration tests, that's likely a setup issue where the agent jar has been added to application
+        // classpath.
+        throw new IllegalStateException(String.format("Agent setup error: agent jar file \"%s\"  likely referenced in JVM or application classpath", agentLocation));
+
+    }
+
     ElasticApmTracer(ConfigurationRegistry configurationRegistry, MetricRegistry metricRegistry, Reporter reporter, ObjectPoolFactory poolFactory,
                      ApmServerClient apmServerClient, final String ephemeralId, MetaDataFuture metaDataFuture) {
         this.metricRegistry = metricRegistry;