Class Farm

packages/jest-worker/src/Farm.ts:24–190

} from './types';

export default class Farm {
  private readonly _computeWorkerKey: WorkerFarmOptions['computeWorkerKey'];
  private readonly _workerSchedulingPolicy: WorkerSchedulingPolicy;
  private readonly _cacheKeys: Record<string, WorkerInterface> =
    Object.create(null);
  private readonly _locks: Array<boolean> = [];
  private _offset = 0;
  private readonly _taskQueue: TaskQueue;

  constructor(
    private readonly _numOfWorkers: number,
    private readonly _callback: WorkerCallback,
    options: WorkerFarmOptions = {},
  ) {
    this._computeWorkerKey = options.computeWorkerKey;
    this._workerSchedulingPolicy =
      options.workerSchedulingPolicy ?? 'round-robin';
    this._taskQueue = options.taskQueue ?? new FifoQueue();
  }

  doWork(
    method: string,
    ...args: Array<unknown>
  ): PromiseWithCustomMessage<unknown> {
    const customMessageListeners = new Set<OnCustomMessage>();

    const addCustomMessageListener = (listener: OnCustomMessage) => {
      customMessageListeners.add(listener);
      return () => {
        customMessageListeners.delete(listener);
      };
    };

    const onCustomMessage: OnCustomMessage = message => {
      for (const listener of customMessageListeners) listener(message);
    };

    const promise: PromiseWithCustomMessage<unknown> = new Promise(
      // Bind args to this function so it won't reference to the parent scope.
      // This prevents a memory leak in v8, because otherwise the function will
      // retain args for the closure.
      ((
        args: Array<unknown>,
        resolve: (value: unknown) => void,
        reject: (reason?: any) => void,
      ) => {
        const computeWorkerKey = this._computeWorkerKey;
        const request: ChildMessage = [CHILD_MESSAGE_CALL, false, method, args];

        let worker: WorkerInterface | null = null;
        let hash: string | null = null;

        if (computeWorkerKey) {
          hash = computeWorkerKey.call(this, method, ...args);
          worker = hash == null ? null : this._cacheKeys[hash];
        }

        const onStart: OnStart = (worker: WorkerInterface) => {