js线程实现

JavaScript 线程实现方法

JavaScript 是单线程语言，但可以通过以下方式模拟多线程或实现并行处理：

Web Workers

Web Workers 允许在后台线程中运行脚本，不会影响主线程的性能。

// 主线程代码
const worker = new Worker('worker.js');
worker.postMessage('Hello Worker');

worker.onmessage = function(e) {
  console.log('Message received from worker', e.data);
};

// worker.js
self.onmessage = function(e) {
  console.log('Message received from main script', e.data);
  self.postMessage('Hello Main');
};

Service Workers

Service Workers 是运行在浏览器后台的脚本，可以拦截网络请求、缓存资源等。

// 注册 Service Worker
if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('/sw.js')
    .then(registration => {
      console.log('ServiceWorker registration successful');
    });
}

SharedArrayBuffer 和 Atomics

共享内存和原子操作可以实现真正的多线程数据共享。

// 主线程
const sharedBuffer = new SharedArrayBuffer(1024);
const sharedArray = new Int32Array(sharedBuffer);

const worker = new Worker('worker.js');
worker.postMessage({buffer: sharedBuffer});

// worker.js
self.onmessage = function(e) {
  const sharedArray = new Int32Array(e.data.buffer);
  Atomics.add(sharedArray, 0, 1);
};

Node.js 工作线程

Node.js 提供了 worker_threads 模块实现多线程。

const { Worker, isMainThread } = require('worker_threads');

if (isMainThread) {
  const worker = new Worker(__filename);
  worker.on('message', (msg) => {
    console.log(msg);
  });
} else {
  parentPort.postMessage('Hello from worker');
}

异步编程

虽然不创建新线程，但 async/await 和 Promise 可以实现非阻塞操作。

async function fetchData() {
  const response = await fetch('https://api.example.com/data');
  const data = await response.json();
  return data;
}

这些方法各有适用场景：Web Workers 适合 CPU 密集型任务，Service Workers 适合离线应用和缓存，Node.js 工作线程适合服务器端并行处理，异步编程则适合 I/O 密集型操作。