在最开始，我们要弄清楚node会什么会存在阻塞？
node是这么标榜自己的：“在node中除了代码，所有一切都是并行执行的！”
意思是，Node.js可以在不新增额外线程的情况下，依然可以对任务进行并行处理 —— Node.js是单线程的。
也就是说，我们启动的web服务器，监听8888端口的start方法，是单线程的。
如果某一个请求耗时，那么后面的请求要等上一个请求完成之后才执行，这显然是不合理的！
如requestHandlers中start handler：
function start() { ???console.log("Request handler ‘start‘ was called."); ???function sleep(milliSeconds) { ???????var startTime = new Date().getTime(); ???????while (new Date().getTime() < startTime + milliSeconds); ???} ???sleep(10000); ???return "Hello Start";}我们可以使用child_process模块来实现非阻塞操作，其实就是一个异步操作，强调一点，耗时操作通常都需要通过异步操作来处理。
一种错误的示范：
var exec = require("child_process").exec;function start() { ?console.log("Request handler ‘start‘ was called."); ?var content = "empty"; ?exec("ls -lah", function (error, stdout, stderr) { ???content = stdout; ?}); ?return content;}function upload() { ?console.log("Request handler ‘upload‘ was called."); ?return "Hello Upload";}exports.start = start;exports.upload = upload;错误原因，exec异步操作后面的不能再跟同步代码，一个简单的例子，juqery ajax请求成功后的后续操作应该在success中处理，而不应该再ajax整个代码块后面处理。
既然后续操作都要在异步回调函数中实现，所以response的处理就要移步至handler中实现。
server.js
var http = require("http");var url = require("url");function start(route, handle) { ?function onRequest(request, response) { ???var pathname = url.parse(request.url).pathname; ???console.log("Request for " + pathname + " received."); ???route(handle, pathname, response); ?} ?http.createServer(onRequest).listen(8888); ?console.log("Server has started.");}exports.start = start;router.js
function route(handle, pathname, response) { ?console.log("About to route a request for " + pathname); ?if (typeof handle[pathname] === ‘function‘) { ???handle[pathname](response); ?} else { ???console.log("No request handler found for " + pathname); ???response.writeHead(404, {"Content-Type": "text/plain"}); ???response.write("404 Not found"); ???response.end(); ?}}exports.route = route;requestHandler.js
var exec = require("child_process").exec;
function start(response) {
console.log("Request handler ‘start‘ was called.");
exec("find /",
{ timeout: 10000, maxBuffer: 20000*1024 },
function (error, stdout, stderr) {
response.writeHead(200, {"Content-Type": "text/plain"});
response.write(stdout);
response.end();
});
}
function upload(response) {
console.log("Request handler ‘upload‘ was called.");
response.writeHead(200, {"Content-Type": "text/plain"});
response.write("Hello Upload");
response.end();
}
exports.start = start;
exports.upload = upload;nodejs入门学习笔记二——解决阻塞问题
原文地址：http://www.cnblogs.com/anybus/p/7724994.html