PHP线程安全与非线程安全的区别

Difference between PHP thread safe and non thread safe binaries

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Since the release of PHP 5.2.1 back in Feburary there has been two new binary packages available for Windows, the non thread safe PHP binaries and the non thread safe PECL binaries. Since then I've read many threads in Internet forums where there seems to be a bit of confusion on what these extra binaries are, how they are used, and what effect they have. In this article I'll discuss the pro's and con's of these new binaries.

Since PHP first came to Windows back on the 20th of October 2000 with the release of PHP 3.0.17, the Windows binaries have always been released as thread safe packages. The reason for this is that Windows uses a multi threaded architecture as opposed to the multi proccess architecture of Linux and Unix. The problem this has when using PHP on IIS in CGI mode is that it makes it very slow as CGI was built on a multi process model, not a multi threaded model. On the flip side the problem this has when using PHP on IIS with the much faster ISAPI module is that there are several popular PHP extensions that have been developed with only Unix/Linux in mind (multi proccess model), and actually cause the PHP ISAPI module to crash on IIS. This making CGI the most stable environment for PHP on IIS, with the major disadvantage that it is terribly slow due to it having to load and unload the entire PHP environment from memory everytime there is a request.

There have been a few options available for a while to get PHP performing well on IIS. Firstly is the use of an opcode cache such as eAccelerator which stores PHP scripts in a partically precompiled state on disk and/or memory which drastically decreases script execution time. Another option is to configure IIS to use PHP in FastCGI mode which allows PHP processes to be recycled rather than killed off after each PHP request and also allows you to run several PHP processes at once, making PHP much much faster with the added bonus that as it is using the CGI interface there is little or no incompatibility issues with PHP extensions. This is still the fastest way to serve PHP, and is the way the IIS Aid PHP Installer is configured to install PHP on your IIS Environment.

What the non thread safe binaries allow you to do is to configure IIS (and other Windows based webservers) to use PHP as a standard CGI interface with massively increased performance as the PHP process is not required to wait for thread syncronisation. The performance increase is not to be sneezed at either as I've seen figures of upto 40% mentioned (though I'm yet to confirm myself), but it is still not as fast as the opcode/FastCGI method mentioned above. One of the biggest catches I've seen people getting themselves hooked on is that non thread safe binaries cannot be reliably used with the thread safe ones, and vise versa. This means that (for the moment at least) you cannot use opcode cache systems such as eAccelerator to give your non thread safe PHP environment a boost in the arm as they are all currently compiled as thread safe.

If the non thread safe binaries are not as fast as what you can configure the thread safe binaries to be then what is the point you ask? Here we come back to FastCGI, and in particular the efforts Microsoft have been making over the last year or so with the development of their own FastCGI handler. This new FastCGI handler from Microsoft enables you to configure the non thread safe PHP binaries in FastCGI mode, which is one massive shot in the arm for performance. Easiest way to put it is using the non thread safe PHP binaries with Microsoft's new FastCGI handler is like putting twin turbos on your car (without the inherent risk of blowing up your engine), and there is little doubt in my mind that this will be the future of PHP on IIS.

PHP线程安全与非线程安全的区别

Windows版的PHP从版本5.2.1开始有Thread Safe(线程安全)和None Thread Safe(NTS，非线程安全)之分，这两者不同在于何处？到底应该用哪种？这里做一个简单的介绍。

　　从2000年10月20日发布的第一个Windows版的PHP3.0.17开始的都是线程安全的版本，这是由于与Linux/Unix系统是采用多进程的工作方式不同的是Windows系统是采用多线程的工作方式。如果在IIS下以CGI方式运行PHP会非常慢，这是由于CGI模式是建立在多进程的基础之上的，而非多线程。一般我们会把PHP配置成以ISAPI的方式来运行，ISAPI是多线程的方式，这样就快多了。但存在一个问题，很多常用的PHP扩展是以Linux/Unix的多进程思想来开发的，这些扩展在ISAPI的方式运行时就会出错搞垮IIS。因此在IIS下CGI模式才是 PHP运行的最安全方式，但CGI模式对于每个HTTP请求都需要重新加载和卸载整个PHP环境，其消耗是巨大的。

　　为了兼顾IIS下PHP的效率和安全，微软给出了FastCGI的解决方案。FastCGI可以让PHP的进程重复利用而不是每一个新的请求就重开一个进程。同时FastCGI也可以允许几个进程同时执行。这样既解决了CGI进程模式消耗太大的问题，又利用上了CGI进程模式不存在线程安全问题的优势。

　　因此，如果是使用ISAPI的方式来运行PHP就必须用Thread Safe(线程安全)的版本；而用FastCGI模式运行PHP的话就没有必要用线程安全检查了，用None Thread Safe(NTS，非线程安全)的版本能够更好的提高效率。