If you are running PHP as CLI and as a "daemon" (i.e. in a loop), this function must be called in each loop to check if new signals are waiting dispatching.
(PHP 5 >= 5.3.0, PHP 7)
pcntl_signal_dispatch — Calls signal handlers for pending signals
The pcntl_signal_dispatch() function calls the signal handlers installed by pcntl_signal() for each pending signal.
Returns TRUE on success or FALSE on failure.
Example #1 pcntl_signal_dispatch() example
<?php
echo "Installing signal handler...\n";
pcntl_signal(SIGHUP, function($signo) {
echo "signal handler called\n";
});
echo "Generating signal SIGHUP to self...\n";
posix_kill(posix_getpid(), SIGHUP);
echo "Dispatching...\n";
pcntl_signal_dispatch();
echo "Done\n";
?>
The above example will output something similar to:
Installing signal handler... Generating signal SIGHUP to self... Dispatching... signal handler called Done
If you are running PHP as CLI and as a "daemon" (i.e. in a loop), this function must be called in each loop to check if new signals are waiting dispatching.
Note that calling pcntl_signal_dispatch() from within a signal handler invoked by a previous pcntl_signal_dispatch() will not trigger handlers for any new pending signals. This means that if you write a CLI daemon which forks off child processes in response to a signal, then those child processes won't be able to respond to signals. This gave me a headache for a while as pcntl_signal_dispatch() doesn't raise any errors when this occurs. One solution is to set a flag within the signal handler and react upon it (by forking off the needed child processes) elsewhere in the parent process's main loop.
Well I misspoke before. It is not enough to process signals outside of the signal handler. They must be processed outside of the tick handler (explicit or implied). So...
Register a tick handler that calls pcntl_signal_dispatch();
In the signal handler, enqueue your signal;
In the main loop of your script, process your signals;
<?php
declare(ticks=1);
global $sig_queue;
global $use_queue;
$sig_queue = array();
$use_queue = true; // set to false to do it the old way
function tick_handler()
{
pcntl_signal_dispatch();
}
function sig_handler($sig)
{
global $sig_queue;
global $use_queue;
if(isset($use_queue) && $use_queue)
{
$sig_queue[] = $sig;
}
else
{
sig_helper($sig);
}
}
function sig_helper($sig)
{
switch($sig)
{
case SIGHUP:
$pid = pcntl_fork();
if($pid) print("forked $pid\n");
break;
default:
print("unhandled sig: $sig\n");
}
}
pcntl_signal(SIGHUP, "sig_handler");
while(true)
{
if($use_queue) foreach($sig_queue as $idx=>$sig)
{
sig_helper($sig);
unset($sig_queue[$idx]);
}
sleep(1);
}
?>
As noted by "me at subsonic dot net" calling pcntl_signal_dispatch() from within a signal handler invoked by a previous pcntl_signal_dispatch() will not trigger handlers for any new pending signals. This seems to be true even if you pcntl_exec() a new PHP processor to execute an entirely different script.
The solution seems to be to explicitly call pcntl_signal_dispatch()inside a ticks_handler() . And use sig_handler(int) as a push function to a queue. Immediately following the call to dispatch in the ticks_handler, pop your queue doing what you would have done in the signal_handler until the queue is empty.