On FastCGI SAPIs this doesn't kill the process, it just makes the fastcgi handler fully recycle PHP at the end of the script rather than just recycling the request state. This includes php-cgi.

I found out a solution for Apache 2. However this works only without threads and only on POSIX compatible OS systems (e.g. Linux, OpenSolaris...).

<?php

// Terminate Apache 2 child process after request has been
// done by sending a SIGWINCH POSIX signal (28).
function kill_on_exit() {
 posix_kill( getmypid(), 28 );
}

register_shutdown_function( 'kill_on_exit' );

?>

Apache child processes are greedy. If they get bloated by a PHP application that requires a lot of memory, they stay that way. The memory is never given back to the OS until that child dies.

You could use MaxRequestsPerChild in Apache to kill all child processes automatically after a certain number of connections. Or you can use apache_child_terminate to kill the child after your memory intensive functions.

Note: apache_child_terminate is not available in Apache 2.0 handler.

In response to sam at liddicott dot com:

it isin't so simple! You should never kill an apache process because it is automatically freed when apache need!

And, if you use apache worker or thread based mpm you risk to kill the entire process!

result: DO NOT USE THIS FUNCTION!

this code will add apache_child_terminate() function if it is not already present.

if (!function_exists("apache_child_terminate")){
function apache_child_terminate(){
register_shutdown_function("killonexit");
}

function killonexit(){
@exec("kill ".getmypid());
}
}