用NodeJS实现集群计算
Node的单个实例运行在单个的线程中，要充分利用多核系统，我们可以运行Node进程集群来处理负载。

也就是说，如果系统有8核，单个Node实例只能使用其中1核，可以利用cluster包的workers概念来充分利用所有的核。有趣的是，它们可以共享同一个端口。

该模块还处于实验阶段。

var cluster = require('cluster');
var http = require('http');
var numCPUs = require('os').cpus().length;
 
if (cluster.isMaster) {
  // Fork workers.
  require('os').cpus().forEach(function(){
    cluster.fork();
  });
  // In case the worker dies!
  cluster.on('exit', function(worker, code, signal) {
    console.log('worker ' + worker.process.pid + ' died');
  });
  // As workers come up.
  cluster.on('listening', function(worker, address) {
    console.log("A worker with #"+worker.id+" is now connected to " +\
     address.address +\
    ":" + address.port);
  });
  // When the master gets a msg from the worker increment the request count.
  var reqCount = 0;
  Object.keys(cluster.workers).forEach(function(id) {
    cluster.workers[id].on('message',function(msg){
      if(msg.info && msg.info == 'ReqServMaster'){
        reqCount += 1;
      }
    });
  });
  // Track the number of request served.
  setInterval(function() {
    console.log("Number of request served = ",reqCount);
  }, 1000);
 
} else {
  // Workers can share the same port!
  require('http').Server(function(req, res) {
    res.writeHead(200);
    res.end("Hello from Cluster!");
    // Notify the master about the request.
    process.send({ info : 'ReqServMaster' });
  }).listen(8000);
}

在一个4核的计算机上，输出如下：

Number of request served =  0
A worker with #2 is now connected to 0.0.0.0:8000
A worker with #4 is now connected to 0.0.0.0:8000
A worker with #1 is now connected to 0.0.0.0:8000
A worker with #3 is now connected to 0.0.0.0:8000
Number of request served =  0
...
Number of request served =  2
..
Number of request served =  4
...
Number of request served =  6