将 AsyncResource 用于 Worker 线程池

¥Using AsyncResource for a Worker thread pool

以下示例显示如何使用 AsyncResource 类为 Worker 池正确提供异步跟踪。其他资源池，例如数据库连接池，可以遵循类似的模型。

¥The following example shows how to use the AsyncResource class to properly provide async tracking for a Worker pool. Other resource pools, such as database connection pools, can follow a similar model.

假设任务是将两个数字相加，使用名为 task_processor.js 的文件，其内容如下：

¥Assuming that the task is adding two numbers, using a file named task_processor.js with the following content:

import { parentPort } from 'node:worker_threads';
parentPort.on('message', (task) => {
  parentPort.postMessage(task.a + task.b);
});const { parentPort } = require('node:worker_threads');
parentPort.on('message', (task) => {
  parentPort.postMessage(task.a + task.b);
});拷贝

它周围的工作池可以使用以下结构：

¥a Worker pool around it could use the following structure:

import { AsyncResource } from 'node:async_hooks';
import { EventEmitter } from 'node:events';
import { Worker } from 'node:worker_threads';

const kTaskInfo = Symbol('kTaskInfo');
const kWorkerFreedEvent = Symbol('kWorkerFreedEvent');

class WorkerPoolTaskInfo extends AsyncResource {
  constructor(callback) {
    super('WorkerPoolTaskInfo');
    this.callback = callback;
  }

  done(err, result) {
    this.runInAsyncScope(this.callback, null, err, result);
    this.emitDestroy();  // `TaskInfo`s are used only once.
  }
}

export default class WorkerPool extends EventEmitter {
  constructor(numThreads) {
    super();
    this.numThreads = numThreads;
    this.workers = [];
    this.freeWorkers = [];
    this.tasks = [];

    for (let i = 0; i < numThreads; i++)
      this.addNewWorker();

    // Any time the kWorkerFreedEvent is emitted, dispatch
    // the next task pending in the queue, if any.
    this.on(kWorkerFreedEvent, () => {
      if (this.tasks.length > 0) {
        const { task, callback } = this.tasks.shift();
        this.runTask(task, callback);
      }
    });
  }

  addNewWorker() {
    const worker = new Worker(new URL('task_processor.js', import.meta.url));
    worker.on('message', (result) => {
      // In case of success: Call the callback that was passed to `runTask`,
      // remove the `TaskInfo` associated with the Worker, and mark it as free
      // again.
      worker[kTaskInfo].done(null, result);
      worker[kTaskInfo] = null;
      this.freeWorkers.push(worker);
      this.emit(kWorkerFreedEvent);
    });
    worker.on('error', (err) => {
      // In case of an uncaught exception: Call the callback that was passed to
      // `runTask` with the error.
      if (worker[kTaskInfo])
        worker[kTaskInfo].done(err, null);
      else
        this.emit('error', err);
      // Remove the worker from the list and start a new Worker to replace the
      // current one.
      this.workers.splice(this.workers.indexOf(worker), 1);
      this.addNewWorker();
    });
    this.workers.push(worker);
    this.freeWorkers.push(worker);
    this.emit(kWorkerFreedEvent);
  }

  runTask(task, callback) {
    if (this.freeWorkers.length === 0) {
      // No free threads, wait until a worker thread becomes free.
      this.tasks.push({ task, callback });
      return;
    }

    const worker = this.freeWorkers.pop();
    worker[kTaskInfo] = new WorkerPoolTaskInfo(callback);
    worker.postMessage(task);
  }

  close() {
    for (const worker of this.workers) worker.terminate();
  }
}const { AsyncResource } = require('node:async_hooks');
const { EventEmitter } = require('node:events');
const path = require('node:path');
const { Worker } = require('node:worker_threads');

const kTaskInfo = Symbol('kTaskInfo');
const kWorkerFreedEvent = Symbol('kWorkerFreedEvent');

class WorkerPoolTaskInfo extends AsyncResource {
  constructor(callback) {
    super('WorkerPoolTaskInfo');
    this.callback = callback;
  }

  done(err, result) {
    this.runInAsyncScope(this.callback, null, err, result);
    this.emitDestroy();  // `TaskInfo`s are used only once.
  }
}

class WorkerPool extends EventEmitter {
  constructor(numThreads) {
    super();
    this.numThreads = numThreads;
    this.workers = [];
    this.freeWorkers = [];
    this.tasks = [];

    for (let i = 0; i < numThreads; i++)
      this.addNewWorker();

    // Any time the kWorkerFreedEvent is emitted, dispatch
    // the next task pending in the queue, if any.
    this.on(kWorkerFreedEvent, () => {
      if (this.tasks.length > 0) {
        const { task, callback } = this.tasks.shift();
        this.runTask(task, callback);
      }
    });
  }

  addNewWorker() {
    const worker = new Worker(path.resolve(__dirname, 'task_processor.js'));
    worker.on('message', (result) => {
      // In case of success: Call the callback that was passed to `runTask`,
      // remove the `TaskInfo` associated with the Worker, and mark it as free
      // again.
      worker[kTaskInfo].done(null, result);
      worker[kTaskInfo] = null;
      this.freeWorkers.push(worker);
      this.emit(kWorkerFreedEvent);
    });
    worker.on('error', (err) => {
      // In case of an uncaught exception: Call the callback that was passed to
      // `runTask` with the error.
      if (worker[kTaskInfo])
        worker[kTaskInfo].done(err, null);
      else
        this.emit('error', err);
      // Remove the worker from the list and start a new Worker to replace the
      // current one.
      this.workers.splice(this.workers.indexOf(worker), 1);
      this.addNewWorker();
    });
    this.workers.push(worker);
    this.freeWorkers.push(worker);
    this.emit(kWorkerFreedEvent);
  }

  runTask(task, callback) {
    if (this.freeWorkers.length === 0) {
      // No free threads, wait until a worker thread becomes free.
      this.tasks.push({ task, callback });
      return;
    }

    const worker = this.freeWorkers.pop();
    worker[kTaskInfo] = new WorkerPoolTaskInfo(callback);
    worker.postMessage(task);
  }

  close() {
    for (const worker of this.workers) worker.terminate();
  }
}

module.exports = WorkerPool;拷贝

如果没有 WorkerPoolTaskInfo 对象添加的显式跟踪，回调似乎与各个 Worker 对象相关联。但是，Worker 的创建与任务的创建无关，并且不提供有关任务计划时间的信息。

¥Without the explicit tracking added by the WorkerPoolTaskInfo objects, it would appear that the callbacks are associated with the individual Worker objects. However, the creation of the Workers is not associated with the creation of the tasks and does not provide information about when tasks were scheduled.

该池可以按如下方式使用：

¥This pool could be used as follows:

import WorkerPool from './worker_pool.js';
import os from 'node:os';

const pool = new WorkerPool(os.availableParallelism());

let finished = 0;
for (let i = 0; i < 10; i++) {
  pool.runTask({ a: 42, b: 100 }, (err, result) => {
    console.log(i, err, result);
    if (++finished === 10)
      pool.close();
  });
}const WorkerPool = require('./worker_pool.js');
const os = require('node:os');

const pool = new WorkerPool(os.availableParallelism());

let finished = 0;
for (let i = 0; i < 10; i++) {
  pool.runTask({ a: 42, b: 100 }, (err, result) => {
    console.log(i, err, result);
    if (++finished === 10)
      pool.close();
  });
}拷贝