Though not available under apache for processing web pages, we do have multi-threading in PHP 🙂
The “pcntl” extension enables multi threading in PHP command line interpreter. That is you can work with php multi threading only from command line. Here’s a code snippet:
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<?php // php pcntl_fork demonstration $fork = pcntl_fork(); // fork a new process echo "\n\n"; switch($fork) { case 0: // It's a child echo "I am a child process of ".posix_getppid()." and my process ID is ".posix_getpid()." \n\n"; break; case -1: // forking failed echo "Something went wrong while \"fork()\"ing a new process :( \n\n"; break; default: // It's the parent pcntl_wait($status); // store the child's exit status echo "I am the parent process with ID: ".posix_getpid()." and my child's ID is: $fork and it's exit status is: $status \n\n"; break; } ?> |
The above example first calls the pcntl_fork() function that creates another process with the same data. That is the current execution data is transferred into a new process. Both the processes will advance in the same way. We will have to differentiate the two processes from this point and assign two different tasks to them.
We differentiate the processes by using the return value of the pcntl_fork() function. If the function is successful in creating a new process, it will return two values — one for each of the processes. And a single value if failed. As you can imagine, if it fails, we will have that single process which started at the beginning. On success, we have two processes running at the same time. Both executes the same php script. But the return value of the pcntl_fork() function varies. So, we should add some code to the script that determines the process which is executing the script and act likewise.
The return value of the function could be of three types:
— A Process ID
— 0 (Zero)
— (-1) (Negative One)
If the process that’s executing the script is the child process, it gets the return value 0. And the parent process gets the process ID of the child. (-1) means the forking failed.
On the above example, we have used posix_getpid() and posix_getppid() functions to retrieve the process ID of that process and it’s parent’s.
The process of forking is a bit tough and it took an hour of total wilderness to understand how it really worked. And to be honest, the PHP manual is not that helpful regarding this extension if I compare to other PHP functionalities.
2 replies on “PHP Multi Threading :)”
I don’t know If I said it already but …This blog rocks! I gotta say, that I read a lot of blogs on a daily basis and for the most part, people lack substance but, I just wanted to make a quick comment to say I’m glad I found your blog. Thanks, 🙂
A definite great read..Tony Brown
[…] ago I wrote a similar post on multi threading in php – http://www.masnun.com/2009/09/07/php-multi-threading.html – which allowed us to fork a new process and execute codes in parallel. While it often served […]