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HomeBackend DevelopmentPHP TutorialPHP中Session引起的脚本阻塞问题解决办法_php实例


解决session阻塞问题的办法:在session操作完成后调用session_write_close()即可避免此问题;


案例一:

使用session过程中,在开启session后,同一浏览器,执行同一程序,不同页面会被锁。不同浏览器不会出现这种情况。

  疑问:是不是session_start导致了阻塞?

   于是,我写了几个页面测试了一下,发现是session导致了阻塞,而其他两种情况不会造成阻塞。

   查了下PHP的Bug列表,发现有人提出了这个问题:

复制代码 代码如下:
Description:
------------
Calling session_start() appears to wait until other scripts have exited

that are using the same session. My guess is the 1st request locks the
session file for exclusive use, and the second request blocks until it
can open it.

    PHP官方的回复是:

复制代码 代码如下:
Thank you for taking the time to write to us, but this is not a bug.This is expected, the session file is locked to avoid corruption.

    结合了PHP的Session机制,找到了阻塞的原因。由于PHP的Session信息是写入文件的,1个客户端占有1个session文件。因此,当 session_start被调用的时候,该文件是被锁住的,而且是以读写模式锁住的(因为程序中可能要修改session的值),这样,第2次调用 session_start的时候就被阻塞了。

    最简解决方法:

    查了PHP的手册,发现一个session_write_close函数,作用是Write session data and end session,也就是写session的数据,同时关闭这个session。因此,我们可以在用完session之后,调用这个函数关闭session 文件即可解除锁定。一般,session是用来记录用户身份信息的,以便PHP进行身份认证,因此完全可以将session的读写放在页面刚开始执行的时 候,在执行完以后,马上调用session_write_close函数即可。


案例二:

上回说要改opencart其实是给opencart加一个抓取淘宝上的产品的功能,但是弄完后发现一个问题,就是当脚本在抓取的时候,因为这个过程比较慢,这个时候其他所有脚本的执行都被阻塞了,直到抓取完其他脚本才能依次执行。研究了半天没有结果,在知乎上问了下可能是session的问题,需要调用session_write_close()来解决,那么这个session_write_close()是干嘛用的呢,手册上这样写的:

复制代码 代码如下:

结束当前session,保存session数据。

session数据通常会在脚本执行结束后被保存而并不需要调用session_write_close(),但是为保护session在任何时候都只能被一个脚本执行写操作,session的数据会被锁住。当同时使用框架网页和session时你会发现,框架里的网页会因为这个个锁定而逐个载入。你可以通过在所有的session数据修改保存结束后马上结束session来加快载入时间。

这就很好的解释了为什么我的抓取脚本会阻塞其他页面的原因。所以,如果你有一个需要执行时间比较长并用到session的ajax请求的话,就需要在服务器端调用session_write_close(),不然你的其他页面就都会被挂起直到请求结束!!!

 

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