我刚开始学习node.js。我有以下（服务器）示例：

var app = require("express").createServer();
app.listen(80);

function fail(req, res, next) { setTimeout(next, 10); }
function success() {
    return function(req, res, next) { setTimeout(next, 10); };
}
app.get("/success0", success(), function(req, res, next) { res.send("0"); });
app.get("/success1", success(), function(req, res, next) { res.send("1"); });
app.get("/fail0", fail, function(req, res, next) { res.send("0"); });
app.get("/fail1", fail, function(req, res, next) { res.send("1"); });

如果我同时调用/fail 0和/fail 1，其中一个会成功，另一个会失败并出现404错误。调用/success 0和success 1可以正常工作。有人能告诉我为什么一个有效而另一个无效吗？下面是我的测试客户：

var http = require("http");
var sys = require("sys");

for(var i = 0; i < 10; i++) {
    var io = http.createClient(80, "localhost");
    var request = io.request("GET", "/fail" + (i%2), {host:"localhost"});
    request.on("response", function(response) {
        var body = "";
        response.on("data", function(data) { body += data; });
        response.on("end", function() {
            sys.puts(response.statusCode + ":" + body);
        });
    }).end();
}

在客户端上运行将返回：

404:Cannot GET /fail0
200:1
404:Cannot GET /fail0
200:1
404:Cannot GET /fail0
200:1
404:Cannot GET /fail0
200:1
404:Cannot GET /fail0
200:1