fix: add option to disable worker_threads in jest-worker

CHANGELOG.md

@@ -52,6 +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))
 
 ### Fixes
 
@@ -129,6 +130,7 @@
 - `[jest-util]` [**BREAKING**] Remove long-deprecated globals for fake timers ([#7285](https://github.com/facebook/jest/pull/7285))
 - `[*]` [**BREAKING**] Upgrade to Micromatch 3 ([#6650](https://github.com/facebook/jest/pull/6650))
 - `[*]` [**BREAKING**] Remove regenerator-runtime injection ([#7595](https://github.com/facebook/jest/pull/7595))
+- `[jest-worker]` Disable `worker_threads` to avoid issues with libraries to ready for it ([#7681](https://github.com/facebook/jest/pull/7681))
 - `[docs]` Fix message property in custom matcher example to return a function instead of a constant. ([#7426](https://github.com/facebook/jest/pull/7426))
 - `[jest-circus]` Standardize file naming in `jest-circus` ([#7301](https://github.com/facebook/jest/pull/7301))
 - `[docs]` Add synchronous test.each setup ([#7150](https://github.com/facebook/jest/pull/7150))

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

@@ -155,6 +155,7 @@ 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

@@ -672,6 +672,7 @@ 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

@@ -96,6 +96,7 @@ 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

@@ -45,6 +45,8 @@ Node 10 shipped with [worker-threads](https://nodejs.org/api/worker_threads.html
 
 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`.
+
 ## API
 
 The only exposed method is a constructor (`Worker`) that is initialized by passing the worker path, plus an options object.
@@ -89,6 +91,10 @@ 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)
+
+`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`.
+
 ## Worker
 
 The returned `Worker` instance has all the exposed methods, plus some additional ones to interact with the workers itself:

packages/jest-worker/src/WorkerPool.js

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

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

@@ -101,4 +101,33 @@ describe('WorkerPool', () => {
       onEnd,
     );
   });
+
+  it('should avoid NodeThreadWorker if passed disableWorkerThreads', () => {
+    jest.mock('worker_threads', () => 'Defined');
+    const workerPool = new WorkerPool('/path', {
+      disableWorkerThreads: true,
+      forkOptions: {},
+      maxRetries: 1,
+      numWorkers: 1,
+      workerId: 0,
+      workerPath: '/path',
+    });
+
+    const onStart = () => {};
+    const onEnd = () => {};
+    workerPool.send(0, {foo: 'bar'}, onStart, onEnd);
+
+    expect(ChildProcessWorker).toBeCalledWith({
+      forkOptions: {},
+      maxRetries: 1,
+      workerId: 0,
+      workerPath: '/path',
+    });
+    expect(NodeThreadWorker).not.toBeCalled();
+    expect(workerPool._workers[0].send).toBeCalledWith(
+      {foo: 'bar'},
+      onStart,
+      onEnd,
+    );
+  });
 });

packages/jest-worker/src/index.js

@@ -77,6 +77,7 @@ export default class JestWorker {
     this._options = {...options};
 
     const workerPoolOptions: WorkerPoolOptions = {
+      disableWorkerThreads: this._options.disableWorkerThreads || 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

@@ -70,13 +70,15 @@ export type FarmOptions = {
     workerPath: string,
     options?: WorkerPoolOptions,
   ) => WorkerPoolInterface,
+  disableWorkerThreads?: boolean,
 };
 
 export type WorkerPoolOptions = {|
   setupArgs: Array<mixed>,
   forkOptions: ForkOptions,
   maxRetries: number,
   numWorkers: number,
+  disableWorkerThreads: boolean,
 |};
 
 export type WorkerOptions = {|