Calling a function in a background thread / process (forking) - php

Question

I have code that's somewhat like this:
($i=0; $i < 100; $i++)
{
do ($foo[$i]);
}
The above is a time intensive task, and I was hoping to be able to create a function, and call it twice like below
function wrapper($start;$end)
{
($i=$start; $i < $end; $i++)
{
do ($foo[$i]);
}
}
//have both of these run in parallel
wrapper(0,50);
wrapper(51,100);
I looked at Gearman but I cannot use it as I cannot install the gearman server (since I'm on a shared server). It seems like the way to achieve this would be by forking. I tried reading up a lot about it, but documentation and support is scant. Any help / wireframe code would be appreciated.
To define my question, how could I call wrapper() passing in arguments such that it executes in a child process. Also, its important that I be able to register a callback function.
Additional Details: PHP 5.3, running on Linux server. Script is executed by cgi-fcgi.
I think this is how I am supposed to spawn a child process, but how can I use it to spawn multiple child processes? And how do I register a callback function?
$pid = pcntl_fork();
if ( $pid == -1 ) {
// Fork failed
exit(1);
} else if ( $pid ) {
// The parent process
//should I repeat this same code here to spawn another child process?
} else {
// the child process
//can I call wrapper from here and will it run in this child process?

Answer 1

From "Tudor Barbu's professional blog"
(http://blog.motane.lu/2009/01/02/multithreading-in-php/)
require_once( 'Thread.php' );
// test to see if threading is available
if( ! Thread::isAvailable() ) {
die( 'Threads not supported' );
}
// function to be ran on separate threads
function paralel( $_limit, $_name ) {
for ( $index = 0; $index < $_limit; $index++ ) {
echo 'Now running thread ' . $_name . PHP_EOL;
sleep( 1 );
}
}
// create 2 thread objects
$t1 = new Thread( 'paralel' );
$t2 = new Thread( 'paralel' );
// start them
$t1->start( 10, 't1' );
$t2->start( 10, 't2' );
// keep the program running until the threads finish
while( $t1->isAlive() && $t2->isAlive() ) {
}
Download Thread.php

Answer 2

If you are using Linux you can take advantage of the command line and do
public function newWrapperInstance($start,$end){
exec('bash -c "exec nohup setsid php-cli yourFile.php '.$start.' '.$end.' > /dev/null 2>&1 &"');
}
This will create a new instance of PHP in the background and detach itself from the exec function in the primary thread.
Warning:
The only downside is you can't control what those threads do once they are created.