I'm currently working with PHP-CLI in order to write a comprensive multithread server framework, using the following PHP modules:
-PCNTL (for process forking)
-SOCKETS (for managing of sockets...)
-SYSVSEM (semaphores to syncronyze threads)
-SYSVSHM (for sharing data between threads)
-XMLRPC (the best object broking for me)

I noticed a strange behaviour of my apps when i use the PHP4.3 executable; the following test script does not work under 4.3, while it works under 4.2.

<?php
define (PULL_TIME,"1");		//event check frequency (secs)

function usr1_handle($signal){
	 if ($signal==SIGUSR1) 
	 print time() . "-Received signal!\n";

}

print "Server starting at " . time() . " ...\n";

$pid=pcntl_fork();
if ($pid==0) {
	// this is the child
   pcntl_signal(SIGUSR1, "usr1_handle");
sleep(5);
$i = 0;
while(true) {sleep(1);}

} else {
	//this is the parent
sleep(5);
while(true) {
   posix_kill($pid,SIGUSR1);
   sleep(PULL_TIME);
}
}
?>

No backtrace avaible, PHP does not crash, simply do nothing.