nodejs实现多线程例子

Node.js 是单线程的，但是可以通过 cluster 模块实现多进程。下面是一个简单的多进程例子：

const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;

if (cluster.isMaster) {
  console.log(`Master ${process.pid} is running`);

  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }

  cluster.on('exit', (worker, code, signal) => {
    console.log(`worker ${worker.process.pid} died`);
  });
} else {
  console.log(`Worker ${process.pid} started`);

  http.createServer((req, res) => {
    res.writeHead(200);
    res.end('Hello World\n');
  }).listen(8000);

  console.log(`Worker ${process.pid} started listening on port 8000`);
}

这个例子创建了多个 worker 进程，每个 worker 进程都监听 8000 端口，当接收到请求时返回 "Hello World"。当一个 worker 进程意外退出时，主进程会重新启动一个新的 worker 进程来代替它。