Executing functions parallelly in PHP

Can PHP call a function and don't wait for it to return? So something like this:

function callback($pause, $arg) {
    sleep($pause);
    echo $arg, "\n";
}

header('Content-Type: text/plain');
fast_call_user_func_array('callback', array(3, 'three'));
fast_call_user_func_array('callback', array(2, 'two'));
fast_call_user_func_array('callback', array(1, 'one'));

would output

one (after 1 second)
two (after 2 seconds)
three (after 3 seconds)

rather than

three (after 3 seconds)
two (after 3 + 2 = 5 seconds)
one (after 3 + 2 + 1 = 6 seconds)

Main script is intended to be run as a permanent process (TCP server). callback() function would receive data from client, execute external PHP script and then do something based on other arguments that ar开发者_开发问答e passed to callback(). The problem is that main script must not wait for external PHP script to finish. Result of external script is important, so exec('php -f file.php &') is not an option.

Edit: Many have recommended to take a look at PCNTL, so it seems that such functionality can be achieved. PCNTL is not available in Windows, and I don't have an access to a Linux machine right now, so I can't test it, but if so many people have advised it, then it should do the trick :)

Thanks, everyone!

On Unix platforms you can enable the PCNTL functions, and use pcntl_fork to fork the process and run your jobs in child processes.

Something like:

function fast_call_user_func_array($func, $args) {
  if (pcntl_fork() == 0) {
    call_user_func_array($func, $args);
  }
}

Once you call pcntl_fork, two processes will execute your code from the same position. The parent process will get a PID returned from pcntl_fork, while the child process will get 0. (If there's an error the parent process will return -1, which is worth checking for in production code).

You can check out PHP Process Control:

http://us.php.net/manual/en/intro.pcntl.php

Note: This is not threading, but the handling of separate processes. There is more overhead attached.

Wouldn't it solve your problem to fork, keeping the parent process free for other connections & actions? See http://www.php.net/pcntl_fork. If you need an answer back you could possibly listen to a socket in the parent, and write with the child. A simple while(true) loop with a read could possibly do, and probably you already have that basic functionality if you run a permanent TCP server. Another option would be to keep track of your childprocess-ids, keep a accessable store somewhere (file/database/memcached etc), with a pcnt_wait in the main process with a WNOHANG to check which process has exited, and retrieve the data from the store.

You can do some threading in PHP if you use the method pcntl_fork.

http://ca.php.net/manual/en/function.pcntl-fork.php

I have never use this myself, but the are some good example of how to use it on php.net.

PHP doesn't have this functionality as far as I know

You can emulate the function using a different technique, like this one: Parallel functions in PHP

PHP does not support multi-threading, so there's no other option than taking advantage of the OS or the web server multi processing capabilities. Note that actually you can fetch both the result and output of exec:

string exec ( string $command [, array &$output [, int &$return_var ]] )

You can, at least, prevent the parent process from hanging until the child process is done by ignoring the child signals using pcntl_signal(SIGCHLD, SIG_IGN).

So, let's say you want to fork a process and execute another PHP function that takes a while without making the parent wait for it to finish (since you want the main process to finish in a timely manner):

pcntl_signal(SIGCHLD, SIG_IGN);
$pid = pcntl_fork();
if ($pid < 0) {
  exit(0);
} elseif (!$pid) {
  my_slow_function();
  exit(0);
}
// Parent keeps executing and finishes before the child does

If you want to execute a slow external script as the child process, pcntl_exec is handy:

$script = array('/path/to/my/script'); // E.g. /home/my_user/my_script.php
pcntl_exec('/path/to/program/executable',$script); // E.g. /usr/bin/php