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问个有关问题哟不知道如何标题应该如何取

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Jun 13, 2016 am 11:15 AM

apachenbspnginxphpselect

问个问题哟不知道怎么标题应该怎么取
就当时标题党吧

服务器上有一个php 文件  比如是1.php

当别人请求这个文件的时候
这个文件就会被执行  然后返回给客户端执行后的东西

我的问题是
当a客户访问的时候1.php的时候  这是服务器还没有执行完,
突然后b客户也来访问了这是1.php是等返回了a的请求在执行b的请求了,还是可以同时执行b的请求

------解决方案--------------------
同时执行b的请求
------解决方案--------------------
其实这涉及到网络模型的问题了。
你知道为什么现在都推崇nginx来取代apache，为什么nginx处理并发问题比apache要强很多吗？

因为apache采用的是linux旧版本内核的select模型，而nginx采用的是2.6+版本的epool模型。

回到具体你说的这个问题上，如果b客户来访问时，服务器等待a客户的处理结果再接受b的请求，这就是select模型的工作方式。从接收到请求后之后，同一个进程会一直follow这整个握手过程，知道response结束。这种模型也很容易遭到ddos攻击。

而epool模型，是异步的。服务器接收到一个请求后，由一个主进程负责把任务合理分工开，有个负责分发任务的线程只负责分发任务，剩余的事情委托给其他线程去处理，其他线程处理完毕后，会callback一下主进程可以response了，然后返回给相应客户端。这样的工作方式，每个请求都不会相互阻塞。

不过这样解释后，你可能会不明白，难道说apache就没法处理并发任务了？一个请求阻塞了，其他的请求都进不来了？当然不是，apache worker模式下会开n个进程，所谓的阻塞，也只会阻塞住一个进程。但select模型的这种工作方式确实效率很低。

这部分知识，你可以去参考libevent

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