(PHP 4 >= 4.3.0, PHP 5, PHP 7, PHP 8)

pcntl_alarmSet an alarm clock for delivery of a signal


pcntl_alarm(int $seconds): int

Creates a timer that will send a SIGALRM signal to the process after the given number of seconds. Any call to pcntl_alarm() will cancel any previously set alarm.



The number of seconds to wait. If seconds is zero, no new alarm is created.

Valores devueltos

Returns the time in seconds that any previously scheduled alarm had remaining before it was to be delivered, or 0 if there was no previously scheduled alarm.

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User Contributed Notes 2 notes

kuba at valentine dot dev
2 years ago
This is that universal timeout functionality you dreamed about and always wanted to have and guess what - it's as reliable as it gets, it's basically bulletproof. It can interrupt absolutely anything you throw at it and more, you name it - socket_connect(), socket_read(), fread(), infinite while() loops, sleep(), semaphores - seriously, any blocking operation. You can specify your own handler and just get over anything that normally would make your code unresponsive.

* Because we shouldn't handle asynchronous
* events in synchronous manner.

* Some flag we can change to know for sure
* that our operation timed out.
$timed_out = FALSE;

* Register SIGALRM signal handler to avoid
* getting our process killed when signal arrives.
pcntl_signal(SIGALRM, function($signal) use (&$timed_out) {
$timed_out = TRUE;

* Now we set our timeout for 2 seconds, but it's not set in stone
* we can call pcntl_alarm() anytime to extend or to turn if off.

* Here we do something with unpredictable outcome that could
* possibly block our program for a very long time.
* I like sockets as an example, but it can be anything.
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
$connection = socket_connect($socket, 'irc.ircnet.com', 6667);

* If our blocking operation didn't timed out then
* timer is still ticking, we should turn it off ASAP.
$timed_out || pcntl_alarm(0);

* And now we do whatever we want to do.
$status = $connection ? 'Connected.' : ($timed_out ? 'Timed out.' : socket_strerror(socket_last_error($socket)));
'STATUS: '. $status . PHP_EOL;
4 years ago
Use pcntl_signal_dispatch() to catch the signal, don't use declare(ticks=1) because it is ineffcient

(SIGALRM, function () {
'Received an alarm signal !' . PHP_EOL;


while (
true) {
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