How to run a PHP script asynchronously?

Question

I am creating a PHP script that will be run via the command line. As part of this script, there are times where I might need to spawn/fork a different script that could take a long time to complete. I don't want to block the original script from completing. If I were doing this with JavaScript, I could run AJAX requests in the background. That is essentially what I am trying to do here. I don't need to know when the forks complete, just that they start and complete themselves.

How can I run these PHP scripts asynchronously?

foreach ($lotsOfItems as $item) {
    if ($item->needsExtraHelp) {
        //start some asynchronous process here, and pass it $item
    }
}

Answer 1

$pids = array();
foreach ($lotsOfItems as $item) {
    if ($item->needsExtraHelp) {
        $pid = pcntl_fork();
        if ($pid == 0) {
           // you're in the child
           var_dump($item);
           exit(0); // don't forget this one!!
        } else if ($pid == -1) {
           // failed to fork process
        } else {
           // you're in the parent
           $pids[] = $pid;
        }
    }

    usleep(100); // prevent CPU from peaking
    foreach ($pids as $pid) {
        pcntl_waitpid($pid, $exitcode, WNOHANG); // prevents zombie processes
    }
}

Answer 2

Looking the user contributed notes on exec, it looks like you could use it, check out:

http://de3.php.net/manual/en/function.exec.php#86329

<?php 
function execInBackground($cmd) { 
    if (substr(php_uname(), 0, 7) == "Windows"){ 
        pclose(popen("start /B ". $cmd, "r"));  
    } 
    else { 
        exec($cmd . " > /dev/null &");   
    } 
} 
?> 

This will execute $cmd in the background (no cmd window) without PHP waiting for it to finish, on both Windows and Unix.