Does PHP support asynchronous programming?

Question

I'm new to PHP. I am familiar with ASP.NET which support asynchronous programming. That is, if one request needs to do some I/O job. It is suggested to program the web page with BeginProcess/EndProcess way. The asynchronous programming is key to improve scalability.

I'm wondering whether there is counterpart of asynchronous programming(BeginXXXX/EndXXXX) in PHP world.

If the request is doing IO, what else is it doing while the IO is going on? Why not give a story of what is happening in PHP and see how you may approach it to take advantage of what PHP offers. — James Black, Nov 15 '09 at 15:25
In ASP.NET, each request is handled in one thread. Since threads as resources are limited, we don't want threads to be blocked on I/O operation. And, thread pool size is always limited in ASP.NET. So, Begin/End patterns are necessary. I suppose it is different story for PHP. Each request is handled in single process? and it doesn't matter to fork process to handle requests. So, this Begin/End asynchronous programming model is not necessary. — Morgan Cheng, Nov 16 '09 at 02:12

Darin Dimitrov · Accepted Answer · 2009-11-15T13:37:27.043

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In .NET BeginXXX/EndXXX paradigm relies heavily on threading, while on PHP I am not sure that you could even start a new thread (except maybe the PECL package).

FastCGI is the alternative to multithreading in most interpreted languages. Instead of spawning new threads it uses processes, but as spawning a new process is expensive, it keeps a reusable process pool just as the ThreadPool in .NET.

edited Nov 15 '09 at 13:37

answered Nov 15 '09 at 13:24

Darin Dimitrov

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Sad news. So, what we can do is to fork process? – Morgan Cheng Nov 15 '09 at 13:25
Yes you can fork processes but as this is an expensive operation I am not sure that you will get much performance improvements. Of course, as always you might have to measure. – Darin Dimitrov Nov 15 '09 at 13:27
I suppose forking processes should be light weighted in *nix OS. – Morgan Cheng Nov 15 '09 at 13:28
To clarify the previous comment, take a look at this [link](http://stackoverflow.com/questions/6133574/how-to-articulate-the-difference-between-asynchronous-and-parallel-programming). – CyberMonk Aug 01 '12 at 16:26
at the end of the day, u're doing a blocking I/O call no matter what, right? – tugberk Jul 21 '13 at 14:47

MeLight · Answer 2 · 2009-11-15T16:06:40.577

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If the I/O is performed with sockets or files you should use stream_socket_select() or stream_select() respectively (similar to system calls in C/C++).

Here's a simple command line chat tutorial done with PHP: Simple PHP socket-based terminal chat

Note: This is not a general multi-threading solution, but a simple solution for situations where you need "semi-parallel" I/O

edited Nov 15 '09 at 16:06

answered Nov 15 '09 at 15:38

MeLight

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score 0 · Answer 3 · answered Nov 15 '09 at 13:32

The core has a set of process control functions, including the ability to fork a process. I don't know that I'd use these in a web script, but have used them in command line scripts before.

http://www.php.net/manual/en/book.pcntl.php

http://www.php.net/manual/en/pcntl.example.php

score 0 · Answer 4 · answered Nov 15 '09 at 17:15

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Here's an interesting link on the subject of PHP multiplexing with PHP4 and PHP5 samples:

http://netevil.org/blog/2005/may/guru-multiplexing

answered Nov 15 '09 at 17:15

Barnabas Kendall

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score 0 · Answer 5 · answered Nov 15 '09 at 17:23

PHP doesn't, but you could use AJAX once the page has loaded, which will allow asynchronous requests.

Honestly though, there is no point. If you really want that heavyweight of a back end, you're better off writing a separate program that does the heavy lifting. PHP modules are written in pure C as far as I'm aware, so you should be able to use that and then call your own custom function from PHP.

score 0 · Answer 6 · answered Feb 22 '12 at 00:58

Using stream_select you can create child processes via a HTTP request. Checkout the code in http://drupal.org/project/httprl for some ideas on how to do this. I plan on pushing this library to github once I get it more polished; something that can be ran outside of drupal. But for now it lives in Drupal land.

Does PHP support asynchronous programming?

6 Answers6