What is thread safe or non-thread safe in PHP

Question

I saw different binaries for PHP  like non-thread or thread safe   What does this mean    What is the difference between these packages

User · Answer

As per PHP Documentation  What does thread safety mean when downloading PHP   Thread Safety means that binary can work in a multithreaded webserver context  such as Apache 2 on Windows  Thread Safety works by creating a local storage copy in each thread  so that the data won t collide with another thread  So what do I choose  If you choose to run PHP as a CGI binary  then you won t need thread safety  because the binary is invoked at each request  For multithreaded webservers  such as IIS5 and IIS6  you should use the threaded version of PHP   Following Libraries are not thread safe  They are not recommended for use in a multi-threaded environment   SNMP  Unix  mSQL  Unix  IMAP  Win Unix  Sybase-CT  Linux  libc5

User · Answer

Needed background on concurrency approaches   Different web servers implement different techniques for handling incoming HTTP requests in parallel  A pretty popular technique is using threads -- that is  the web server will create dedicate a single thread for each incoming request  The Apache HTTP web server supports multiple models for handling requests  one of which  called the worker MPM  uses threads  But it supports another concurrency model called the prefork MPM which uses processes -- that is  the web server will create dedicate a single process for each request   There are also other completely different concurrency models  using Asynchronous sockets and I O   as well as ones that mix two or even three models together  For the purpose of answering this question  we are only concerned with the two models above  and taking Apache HTTP server as an example   Needed background on how PHP  integrates  with web servers   PHP itself does not respond to the actual HTTP requests -- this is the job of the web server  So we configure the web server to forward requests to PHP for processing  then receive the result and send it back to the user  There are multiple ways to chain the web server with PHP  For Apache HTTP Server  the most popular is  mod php   This module is actually PHP itself  but compiled as a module for the web server  and so it gets loaded right inside it   There are other methods for chaining PHP with Apache and other web servers  but mod php is the most popular one and will also serve for answering your question   You may not have needed to understand these details before  because hosting companies and GNU Linux distros come with everything prepared for us   Now  onto your question   Since with mod php  PHP gets loaded right into Apache  if Apache is going to handle concurrency using its Worker MPM  that is  using Threads  then PHP must be able to operate within this same multi-threaded environment -- meaning  PHP has to be thread-safe to be able to play ball correctly with Apache   At this point  you should be thinking  OK  so if I m using a multi-threaded web server and I m going to embed PHP right into it  then I must use the thread-safe version of PHP   And this would be correct thinking  However  as it happens  PHP s thread-safety is highly disputed  It s a use-if-you-really-really-know-what-you-are-doing ground   Final notes  In case you are wondering  my personal advice would be to not use PHP in a multi-threaded environment if you have the choice   Speaking only of Unix-based environments  I d say that fortunately  you only have to think of this if you are going to use PHP with Apache web server  in which case you are advised to go with the prefork MPM of Apache  which doesn t use threads  and therefore  PHP thread-safety doesn t matter  and all GNU Linux distributions that I know of will take that decision for you when you are installing Apache   PHP through their package system  without even prompting you for a choice  If you are going to use other webservers such as nginx or lighttpd  you won t have the option to embed PHP into them anyway  You will be looking at using FastCGI or something equal which works in a different model where PHP is totally outside of the web server with multiple PHP processes used for answering requests through e g  FastCGI  For such cases  thread-safety also doesn t matter  To see which version your website is using put a file containing  lt  php phpinfo      gt  on your site and look for the Server API entry  This could say something like CGI FastCGI or Apache 2 0 Handler   If you also look at the command-line version of PHP -- thread safety does not matter   Finally  if thread-safety doesn t matter so which version should you use -- the thread-safe or the non-thread-safe  Frankly  I don t have a scientific answer  But I d guess that the non-thread-safe version is faster and or less buggy  or otherwise they would have just offered the thread-safe version and not bothered to give us the choice

User · Answer

Apache MPM prefork with modphp is used because it is easy to configure install  Performance-wise it is fairly inefficient  My preferred way to do the stack  FastCGI PHP-FPM  That way you can use the much faster MPM Worker  The whole PHP remains non-threaded  but Apache serves threaded  like it should    So basically  from bottom to top  Linux  Apache   MPM Worker   ModFastCGI  NOT FCGI    or   Cherokee   or   Nginx  PHP-FPM   APC  ModFCGI does not correctly support PHP-FPM  or any external FastCGI applications  It only supports non-process managed FastCGI scripts  PHP-FPM is the PHP FastCGI process manager

User · Answer

For me  I always choose non-thread safe version because I always use nginx  or run PHP from the command line   The non-thread safe version should be used if you install PHP as a CGI binary  command line interface or other environment where only a single thread is used   A thread-safe version should be used if you install PHP as an Apache module in a worker MPM  multi-processing model  or other environment where multiple PHP threads run concurrently

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