Method doWork

packages/jest-worker/src/Farm.ts:44–110

(
    method: string,
    ...args: Array<unknown>
  )

  }

  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) => {
          if (hash != null) {
            this._cacheKeys[hash] = worker;
          }
        };

        const onEnd: OnEnd = (error: Error | null, result: unknown) => {
          customMessageListeners.clear();
          if (error) {
            reject(error);
          } else {
            resolve(result);
          }
        };

        const task = {onCustomMessage, onEnd, onStart, request};

        if (worker) {
          this._taskQueue.enqueue(task, worker.getWorkerId());
          this._process(worker.getWorkerId());
        } else {