在集群中使用http.createServer时，为什么要多次调用http.create服务器的回调

Question

我试图了解集群的工作人员如何为http请求提供服务。我从代码开始http://nodejs.org/api/cluster.html并添加了一些日志记录。

我将以下代码放在server.js中，并使用执行该文件：NODE_DEBUG=集群节点服务器.js

var cluster = require('cluster');
var http = require('http');
var numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
    console.log('number of CPUs: ' + numCPUs);
    // Fork workers.
    for (var i = 0; i < numCPUs; i++) {
        console.log('forking worker ' + i);
        cluster.fork();
    }
    cluster.on('exit', function(worker, code, signal) {
        console.log('worker ' + worker.process.pid + ' died');
    });
} else {
    console.log('worker spawned: ' + cluster.worker.process.pid);
    var someVar = {'b': 1};
    // Workers can share any TCP connection
    // In this case its a HTTP server
    http.createServer(function(req, res) {
        console.log('someVar.b current value: ' + someVar.b + ". someVar.b will be incremented");
        someVar.b = someVar.b + 1;
        console.log('Request being processed by worker: ' + cluster.worker.process.pid);
        res.writeHead(200);
        res.end("hello worldn");
        console.log('response ended by worker: ' + cluster.worker.process.pid);
    }).listen(8000);
}

然后我去了localhost:8000一次，瞧，"helloworld"是我所期望的响应。我没想到的是，一些日志语句被打印了两次：

number of CPUs: 2
forking worker 0
forking worker 1
535,Master Worker 536 online
535,Master Worker 537 online
worker spawned: 536
worker spawned: 537
someVar.b current value: 1. someVar.b will be incremented
Request being processed by worker: 536
response ended by worker: 536
someVar.b current value: 2. someVar.b will be incremented
Request being processed by worker: 536
response ended by worker: 536

具体来说，我预计对于我的服务器的一个请求，以下行只打印一次：

someVar.b current value: X. someVar.b will be incremented
Request being processed by worker: XXX
response ended by worker: XXX

相反，我的函数被同一个工人执行了两次。有人能解释一下吗？

Answer 1

是否检查了req.url？我打赌这两个请求中有一个请求是/favicon.ico。