Fix queue management in jest-worker

CHANGELOG.md

@@ -14,7 +14,8 @@
 - `[jest-changed-files]` Improve default file selection for Mercurial repos ([#7880](https://github.com/facebook/jest/pull/7880))
 - `[jest-validate]` Fix validating async functions ([#7894](https://github.com/facebook/jest/issues/7894))
 - `[jest-circus]` Fix bug with test.only ([#7888](https://github.com/facebook/jest/pull/7888))
-- `[jest-transform]` Normalize config and remove unecessary checks, convert `TestUtils.js` to TypeScript ([#7801](https://github.com/facebook/jest/pull/7801)
+- `[jest-transform]` Normalize config and remove unecessary checks, convert `TestUtils.js` to TypeScript ([#7801](https://github.com/facebook/jest/pull/7801))
+- `[jest-worker]` Fix `jest-worker` when using pre-allocated jobs ([#7934](https://github.com/facebook/jest/pull/7934))
 
 ### Chore & Maintenance
 

packages/jest-worker/src/Farm.ts

@@ -9,6 +9,7 @@ import {
   ChildMessage,
   FarmOptions,
   QueueChildMessage,
+  QueueItem,
   WorkerInterface,
   OnStart,
   OnEnd,
@@ -19,24 +20,25 @@ export default class Farm {
   private _computeWorkerKey: FarmOptions['computeWorkerKey'];
   private _cacheKeys: {[key: string]: WorkerInterface};
   private _callback: Function;
-  private _last: Array<QueueChildMessage>;
+  private _last: Array<QueueItem>;
   private _locks: Array<boolean>;
   private _numOfWorkers: number;
   private _offset: number;
-  private _queue: Array<QueueChildMessage | null>;
+  private _queue: Array<QueueItem | null>;
 
   constructor(
     numOfWorkers: number,
     callback: Function,
     computeWorkerKey?: FarmOptions['computeWorkerKey'],
   ) {
-    this._callback = callback;
-    this._numOfWorkers = numOfWorkers;
     this._cacheKeys = Object.create(null);
-    this._queue = [];
+    this._callback = callback;
     this._last = [];
     this._locks = [];
+    this._numOfWorkers = numOfWorkers;
     this._offset = 0;
+    this._queue = [];
+
     if (computeWorkerKey) {
       this._computeWorkerKey = computeWorkerKey;
     }
@@ -70,6 +72,7 @@ export default class Farm {
       };
 
       const task = {onEnd, onStart, request};
+
       if (worker) {
         this._enqueue(task, worker.getWorkerId());
       } else {
@@ -78,80 +81,82 @@ export default class Farm {
     });
   }
 
-  private _getNextJob(workerId: number): QueueChildMessage | null {
+  private _getNextTask(workerId: number): QueueChildMessage | null {
     let queueHead = this._queue[workerId];
 
-    while (queueHead && queueHead.request[1]) {
+    while (queueHead && queueHead.task.request[1]) {
       queueHead = queueHead.next || null;
     }
 
     this._queue[workerId] = queueHead;
 
-    return queueHead;
+    return queueHead && queueHead.task;
   }
 
   private _process(workerId: number): Farm {
-    if (this.isLocked(workerId)) {
+    if (this._isLocked(workerId)) {
       return this;
     }
 
-    const job = this._getNextJob(workerId);
+    const task = this._getNextTask(workerId);
 
-    if (!job) {
+    if (!task) {
       return this;
     }
 
     const onEnd = (error: Error | null, result: unknown) => {
-      job.onEnd(error, result);
-      this.unlock(workerId);
+      task.onEnd(error, result);
+
+      this._unlock(workerId);
       this._process(workerId);
     };
 
-    this.lock(workerId);
+    task.request[1] = true;
 
-    this._callback(workerId, job.request, job.onStart, onEnd);
-
-    job.request[1] = true;
+    this._lock(workerId);
+    this._callback(workerId, task.request, task.onStart, onEnd);
 
     return this;
   }
 
   private _enqueue(task: QueueChildMessage, workerId: number): Farm {
+    const item = {next: null, task};
+
     if (task.request[1]) {
       return this;
     }
 
     if (this._queue[workerId]) {
-      this._last[workerId].next = task;
+      this._last[workerId].next = item;
     } else {
-      this._queue[workerId] = task;
+      this._queue[workerId] = item;
     }
 
-    this._last[workerId] = task;
+    this._last[workerId] = item;
     this._process(workerId);
 
     return this;
   }
 
   private _push(task: QueueChildMessage): Farm {
     for (let i = 0; i < this._numOfWorkers; i++) {
-      const workerIdx = (this._offset + i) % this._numOfWorkers;
-      this._enqueue(task, workerIdx);
+      this._enqueue(task, (this._offset + i) % this._numOfWorkers);
     }
+
     this._offset++;
 
     return this;
   }
 
-  lock(workerId: number): void {
+  private _lock(workerId: number): void {
     this._locks[workerId] = true;
   }
 
-  unlock(workerId: number): void {
+  private _unlock(workerId: number): void {
     this._locks[workerId] = false;
   }
 
-  isLocked(workerId: number): boolean {
+  private _isLocked(workerId: number): boolean {
     return this._locks[workerId];
   }
 }

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

@@ -200,18 +200,19 @@ describe('Farm', () => {
     workerReply(0, null, 17);
     await p0;
 
-    // Note that the stickiness is not created by the method name or the arguments
-    // it is solely controlled by the provided "computeWorkerKey" method, which in
-    // the test example always returns the same key, so all calls should be
-    // redirected to worker 1 (which is the one that resolved the first call).
+    // Note that the stickiness is not created by the method name or the
+    // arguments it is solely controlled by the provided "computeWorkerKey"
+    // method, which in the test example always returns the same key, so all
+    // calls should be redirected to worker 1 (which is the one that resolved
+    // the first call).
     const p1 = farm.doWork('foo', 'bar');
     workerReply(1, null, 17);
     await p1;
 
-    // The first time, a call with a "1234567890abcdef" hash had never been done
-    // earlier ("foo" call), so it got queued to all workers. Later, since the one
-    // that resolved the call was the one in position 1, all subsequent calls are
-    // only redirected to that worker.
+    // The first time, a call with a "1234567890abcdef" hash had never been
+    // done earlier ("foo" call), so it got queued to all workers. Later, since
+    // the one that resolved the call was the one in position 1, all subsequent
+    // calls are only redirected to that worker.
     expect(callback).toHaveBeenCalledTimes(2); // Only "foo".
     expect(callback).toHaveBeenNthCalledWith(
       1,
@@ -248,11 +249,11 @@ describe('Farm', () => {
     workerReply(1, null, 17);
     await p1;
 
-    // Both requests are send to the same worker
-    // The first time, a call with a "1234567890abcdef" hash had never been done
-    // earlier ("foo" call), so it got queued to all workers. Later, since the one
-    // that resolved the call was the one in position 1, all subsequent calls are
-    // only redirected to that worker.
+    // Both requests are send to the same worker.  The first time, a call with
+    // a "1234567890abcdef" hash had never been done earlier ("foo" call), so
+    // it got queued to all workers. Later, since the one that resolved the
+    // call was the one in position 1, all subsequent calls are only redirected
+    // to that worker.
     expect(callback).toHaveBeenCalledTimes(2);
     expect(callback).toHaveBeenNthCalledWith(
       1,
@@ -269,4 +270,67 @@ describe('Farm', () => {
       expect.any(Function),
     );
   });
+
+  it('checks that locking works, and jobs are never lost', async () => {
+    const hash = jest
+      .fn()
+      // This will go to both queues, but picked by the first worker.
+      .mockReturnValueOnce(0)
+      // This will go to both queues too, but picked by the second worker.
+      .mockReturnValueOnce(1)
+      // This will go to worker 0, now only assigned to it.
+      .mockReturnValueOnce(0)
+      // This will go to worker 1, now only assigned to it.
+      .mockReturnValueOnce(1)
+      // This will go to both queues too, but will wait, since workers are busy.
+      .mockReturnValueOnce(2)
+      // This will only go to the first queue.
+      .mockReturnValueOnce(0)
+      // This will be gone if the queue implementation is wrong.
+      .mockReturnValueOnce(0)
+      // Push onto the second queue; potentially wiping the earlier job.
+      .mockReturnValueOnce(1);
+
+    const farm = new Farm(2, callback, hash);
+
+    // First and second jobs get resolved, so that their hash is sticked to
+    // the right worker: worker assignment is performed when workers reply, not
+    // when the call is made.
+    const p0 = farm.doWork('work-0');
+    const p1 = farm.doWork('work-1');
+    workerReply(0, null, 'response-0');
+    await p0;
+    workerReply(1, null, 'response-1');
+    await p1;
+
+    // Now we perform the rest of the calls (7 resolves before 5 and 6, since 4
+    // is in both queues, and as soon as you resolve 4, 7 will be picked).
+    const p2 = farm.doWork('work-2');
+    const p3 = farm.doWork('work-3');
+    const p4 = farm.doWork('work-4');
+    const p5 = farm.doWork('work-5');
+    const p6 = farm.doWork('work-6');
+    const p7 = farm.doWork('work-7');
+    workerReply(2, null, 'response-2');
+    await p2;
+    workerReply(3, null, 'response-3');
+    await p3;
+    workerReply(4, null, 'response-4');
+    await p4;
+    workerReply(5, null, 'response-7');
+    await p7;
+    workerReply(6, null, 'response-5');
+    await p5;
+    workerReply(7, null, 'response-6');
+    await p6;
+
+    await expect(p0).resolves.toBe('response-0');
+    await expect(p1).resolves.toBe('response-1');
+    await expect(p2).resolves.toBe('response-2');
+    await expect(p3).resolves.toBe('response-3');
+    await expect(p4).resolves.toBe('response-4');
+    await expect(p5).resolves.toBe('response-5');
+    await expect(p6).resolves.toBe('response-6');
+    await expect(p7).resolves.toBe('response-7');
+  });
 });

packages/jest-worker/src/types.ts

@@ -147,12 +147,17 @@ export type ParentMessageError = [
 export type ParentMessage = ParentMessageOk | ParentMessageError;
 
 // Queue types.
+
 export type OnStart = (worker: WorkerInterface) => void;
 export type OnEnd = (err: Error | null, result: unknown) => void;
 
 export type QueueChildMessage = {
   request: ChildMessage;
   onStart: OnStart;
   onEnd: OnEnd;
-  next?: QueueChildMessage;
+};
+
+export type QueueItem = {
+  task: QueueChildMessage;
+  next: QueueItem | null;
 };