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Saturday, October 30, 2010

A discussion about asynchronous programming in PHP and further

I read an article about asynchronous programming in PHP. It declares that lacking asynchronous programming is not limitation from PHP language. However, I think this is obviously the limitation of PHP.

Lacking of multi-thread features is the source of the limitation. PHP programmers have argued that they can use named pipe, node.js, libevent, Curl, Zend_Job, and other process control extensions to implement asynchronous functions in PHP. However, these methods are not core PHP feature. Therefore, there is no guarantee that these functions can be run on all platforms on which core PHP can run. For example, I wonder whether libevent can run on IBM i platform or not. Zend Server for IBM i supports Zend_Job. But it is not in Zend Server CE, which is free. Also, some extensions like PCNTL seems a solution based on multi process with shared memory. It is a inter-process implementation. Multithreading is a inner process implementation.

This limitation of PHP is because of the way of running PHP script too. PHP is known that it has less memory leak problem. This is not surprised as each PHP script is loaded into memory only when it need to be executed. After it is executed, it is flushed out of memory. Of course, PHP has no memory leak as it has no memory at all.This is because PHP inherits from perl as CGI programming language. Somebody will argue that PHP actually has optimizers and extensions like memcache. These make PHP looks like have some memory. However, optimizer is for caching operation code. memcache is for caching some data as a persistent storage. They can not make PHP to have real memory.

Since PHP has no memory, core PHP has no function like PipedInputStream, PipedOutputStream, and multi thread etc. As I presented in an old post, its static modifier means different life scope than other languages do. So, lacking of asynchronous programming feature is the limitation from PHP itself. It is confusing to discuss PHP lacks asynchronous feature and deny it is limitation from PHP language itself.

Also, in servlet world, people has been interested in changing "request per thread" architecture because of the challenge from multiplied Ajax calling from browser side. Leading by Jetty, both Jetty and Tomcat 7.0 has implemented asynchronous servlet API already. I will deeply investigate whether PHP is facing same challenge or not. Or, with Fastcgi, PHP does not need to worry about this at all.


  1. hello, I am having issues with some code I have written in php... an you help me fix something lacking.

  2. can I post the code here? I think I am missing the point in a slight way

  3. Hi palstreet,

    Thank you for comments! You are absolutely welcome to post your code here.

  4. I was looking for this kind of information. Thanks a lot dear.