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

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?

Solution 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

Solution 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.

Comments

[Ayush]

Thanks. This seems like a brilliant wrapper. I'm looking into the code right now

[Kelvin]

The link you reference also says it's bad to use an empty loop to check if threads are alive, because it will use up all your CPU. You should include a sleep in the loop.

[Jason]

@Kelvin, a better solution is to implement a join capability to the library, should be fairly simple to do.

[Sceptical Jule]

How can I start a class method using this approach?