PHP 8.1.22 pcntl_waitpid does not work

[bbonev]

Description

The following code:

<?php
declare(ticks=1);

function dummy() {
	echo "got sigchild\n";
}

pcntl_signal(SIGCHLD,"dummy");

for ($i=0;$i<20;$i++)
	if (pcntl_fork()==0)
		pcntl_exec('/bin/sleep',["0.{$i}"]);

$done=0;
do {
	$st=-1;
	while (($pid=pcntl_waitpid(-1,$st,WNOHANG))>0)
		echo "got pid {$pid}\n";
	if ($pid==0)
		usleep(550);
} while (20>$done);

This loops forever on 8.1.22 but work as expected on 8.1.21 and earlier. In both cases I am getting the SIGCHLD signal but with 8.1.22 pcntl_waitpid always returns zero.

I have tried to get the pcntl.c from 8.1.21 and recompile 8.1.22 with it, then it works. I suspect that the problem is in f39b513 that calls waitpid inside the signal handler without buffering the results for pcntl_waitpid to fetch later (it calls wait4/waitpid), but I did not dig further.

It is also strange that pcntl_waitpid uses wait4/waitpid but pcntl_signal_handler doesn't do the same.

PHP Version

PHP 8.1.22

Operating System

No response

[nielsdos]

That commit is indeed the issue. This has been fixed in the current PHP-8.1 (and 8.2) development branch.