make worker_threads opt-in, not opt-out (#7693)

CHANGELOG.md

@@ -52,7 +52,7 @@
 - `[jest-runner]` Instantiate the test environment class with the current `testPath` ([#7442](https://github.com/facebook/jest/pull/7442))
 - `[jest-config]` Always resolve jest-environment-jsdom from jest-config ([#7476](https://github.com/facebook/jest/pull/7476))
 - `[expect]` Improve report when assertion fails, part 6 ([#7621](https://github.com/facebook/jest/pull/7621))
-- `[jest-worker]` Add `disableWorkerThreads` option to explicitly opt out of `worker_threads` even if available ([#7681](https://github.com/facebook/jest/pull/7681))
+- `[jest-worker]` Add `enableWorkerThreads` option to explicitly opt-in to `worker_threads` if available ([#7681](https://github.com/facebook/jest/pull/7681))
 
 ### Fixes
 

packages/jest-cli/src/reporters/coverage_reporter.js

@@ -155,7 +155,6 @@ export default class CoverageReporter extends BaseReporter {
     } else {
       // $FlowFixMe: assignment of a worker with custom properties.
       worker = new Worker(require.resolve('./coverage_worker'), {
-        disableWorkerThreads: true,
         exposedMethods: ['worker'],
         maxRetries: 2,
         numWorkers: this._globalConfig.maxWorkers,

packages/jest-haste-map/src/index.js

@@ -672,7 +672,6 @@ class HasteMap extends EventEmitter {
       } else {
         // $FlowFixMe: assignment of a worker with custom properties.
         this._worker = (new Worker(require.resolve('./worker'), {
-          disableWorkerThreads: true,
           exposedMethods: ['getSha1', 'worker'],
           maxRetries: 3,
           numWorkers: this._options.maxWorkers,

packages/jest-runner/src/index.js

@@ -96,7 +96,6 @@ class TestRunner {
   ) {
     // $FlowFixMe: class object is augmented with worker when instantiating.
     const worker: WorkerInterface = new Worker(TEST_WORKER_PATH, {
-      disableWorkerThreads: true,
       exposedMethods: ['worker'],
       forkOptions: {stdio: 'pipe'},
       maxRetries: 3,

packages/jest-worker/README.md

@@ -43,9 +43,7 @@ export function hello(param) {
 
 Node 10 shipped with [worker-threads](https://nodejs.org/api/worker_threads.html), a "threading API" that uses SharedArrayBuffers to communicate between the main process and its child threads. This experimental Node feature can significantly improve the communication time between parent and child processes in `jest-worker`.
 
-We will use worker threads where available. To enable in Node 10+, run the Node process with the `--experimental-worker` flag.
-
-You can explicitly opt-out of this by passing `disableWorkerThreads: true`.
+Since `worker_threads` are considered experimental in Node, you have to opt-in to this behavior by passing `enableWorkerThreads: true` when instantiating the worker. While the feature was unflagged in Node 11.7.0, you'll need to run the Node process with the `--experimental-worker` flag for Node 10.
 
 ## API
 
@@ -91,9 +89,9 @@ Provide a custom worker pool to be used for spawning child processes. By default
 
 The arguments that will be passed to the `setup` method during initialization.
 
-#### `disableWorkerThreads: boolean` (optional)
+#### `enableWorkerThreads: boolean` (optional)
 
-`jest-worker` will automatically detect if `worker_threads` are available and use them. However, running under threads comes with [some caveats](https://nodejs.org/api/worker_threads.html#worker_threads_class_worker), and is still experimental, so you can `opt-out` of this and use `disableWorkerThreads: true`.
+`jest-worker` will automatically detect if `worker_threads` are available, but will not use them unless passed `enableWorkerThreads: true`.
 
 ## Worker
 

packages/jest-worker/src/WorkerPool.js

@@ -42,7 +42,7 @@ class WorkerPool extends BaseWorkerPool implements WorkerPoolInterface {
 
   createWorker(workerOptions: WorkerOptions): WorkerInterface {
     let Worker;
-    if (!this._options.disableWorkerThreads && canUseWorkerThreads()) {
+    if (this._options.enableWorkerThreads && canUseWorkerThreads()) {
       Worker = require('./workers/NodeThreadsWorker').default;
     } else {
       Worker = require('./workers/ChildProcessWorker').default;

packages/jest-worker/src/__tests__/WorkerPool.test.js

@@ -77,6 +77,7 @@ describe('WorkerPool', () => {
   it('should create a NodeThreadWorker and send to it', () => {
     jest.mock('worker_threads', () => 'Defined');
     const workerPool = new WorkerPool('/path', {
+      enableWorkerThreads: true,
       forkOptions: {},
       maxRetries: 1,
       numWorkers: 1,
@@ -102,10 +103,9 @@ describe('WorkerPool', () => {
     );
   });
 
-  it('should avoid NodeThreadWorker if passed disableWorkerThreads', () => {
+  it('should avoid NodeThreadWorker if not passed enableWorkerThreads', () => {
     jest.mock('worker_threads', () => 'Defined');
     const workerPool = new WorkerPool('/path', {
-      disableWorkerThreads: true,
       forkOptions: {},
       maxRetries: 1,
       numWorkers: 1,

packages/jest-worker/src/__tests__/thread-integration.test.js

@@ -66,6 +66,7 @@ describe('Jest Worker Process Integration', () => {
 
   it('calls a single method from the worker', async () => {
     const farm = new Farm('/tmp/baz.js', {
+      enableWorkerThreads: true,
       exposedMethods: ['foo', 'bar'],
       numWorkers: 4,
     });
@@ -79,6 +80,7 @@ describe('Jest Worker Process Integration', () => {
 
   it('distributes sequential calls across child processes', async () => {
     const farm = new Farm('/tmp/baz.js', {
+      enableWorkerThreads: true,
       exposedMethods: ['foo', 'bar'],
       numWorkers: 4,
     });
@@ -100,6 +102,7 @@ describe('Jest Worker Process Integration', () => {
 
   it('distributes concurrent calls across child processes', async () => {
     const farm = new Farm('/tmp/baz.js', {
+      enableWorkerThreads: true,
       exposedMethods: ['foo', 'bar'],
       numWorkers: 4,
     });
@@ -128,6 +131,7 @@ describe('Jest Worker Process Integration', () => {
   it('sticks parallel calls to children', async () => {
     const farm = new Farm('/tmp/baz.js', {
       computeWorkerKey: () => '1234567890abcdef',
+      enableWorkerThreads: true,
       exposedMethods: ['foo', 'bar'],
       numWorkers: 4,
     });

packages/jest-worker/src/index.js

@@ -77,7 +77,7 @@ export default class JestWorker {
     this._options = {...options};
 
     const workerPoolOptions: WorkerPoolOptions = {
-      disableWorkerThreads: this._options.disableWorkerThreads || false,
+      enableWorkerThreads: this._options.enableWorkerThreads || false,
       forkOptions: this._options.forkOptions || {},
       maxRetries: this._options.maxRetries || 3,
       numWorkers: this._options.numWorkers || Math.max(os.cpus().length - 1, 1),

packages/jest-worker/src/types.js

@@ -70,15 +70,15 @@ export type FarmOptions = {
     workerPath: string,
     options?: WorkerPoolOptions,
   ) => WorkerPoolInterface,
-  disableWorkerThreads?: boolean,
+  enableWorkerThreads?: boolean,
 };
 
 export type WorkerPoolOptions = {|
   setupArgs: Array<mixed>,
   forkOptions: ForkOptions,
   maxRetries: number,
   numWorkers: number,
-  disableWorkerThreads: boolean,
+  enableWorkerThreads: boolean,
 |};
 
 export type WorkerOptions = {|