Installs a signal handler

Description

pcntl_signal(int $signal, callable|int $handler, bool $restart_syscalls = true): bool

The pcntl_signal() function installs a new signal handler or replaces the current signal handler for the signal indicated by signal.

Parameters

signal

The signal number.

handler

The signal handler. This may be either a callable, which will be invoked to handle the signal, or either of the two global constants SIG_IGN or SIG_DFL, which will ignore the signal or restore the default signal handler respectively.

If a callable is given, it must implement the following signature:

handler(int $signo, mixed $siginfo): void

signal: The signal being handled.
siginfo: If operating systems supports siginfo_t structures, this will be an array of signal information dependent on the signal.

Note:
Note that when you set a handler to an object method, that object's reference count is increased which makes it persist until you either change the handler to something else, or your script ends.

restart_syscalls

Specifies whether system call restarting should be used when this signal arrives.

Return Values

Returns true on success or false on failure.

Changelog

Version	Description
7.1.0	As of PHP 7.1.0 the handler callback is given a second argument containing the siginfo of the specific signal. This data is only supplied if the operating system has the siginfo_t structure. If the OS does not implement siginfo_t NULL is supplied.

Examples

Example #1 pcntl_signal() example

<?php
pcntl_async_signals(true);

// signal handler function
function sig_handler($signo)
{

     switch ($signo) {
         case SIGTERM:
             // handle shutdown tasks
             exit;
             break;
         case SIGHUP:
             // handle restart tasks
             break;
         case SIGUSR1:
             echo "Caught SIGUSR1...\n";
             break;
         default:
             // handle all other signals
     }

}

echo "Installing signal handler...\n";

// setup signal handlers
pcntl_signal(SIGTERM, "sig_handler");
pcntl_signal(SIGHUP,  "sig_handler");
pcntl_signal(SIGUSR1, "sig_handler");

// or use an object
// pcntl_signal(SIGUSR1, array($obj, "do_something"));

echo"Generating signal SIGUSR1 to self...\n";

// send SIGUSR1 to current process id
// posix_* functions require the posix extension
posix_kill(posix_getpid(), SIGUSR1);

echo "Done\n";

?>

Notes

pcntl_signal() doesn't stack the signal handlers, but replaces them.

Dispatch Methods

There are several methods of dispatching signal handlers:

Asynchronous dispatch with pcntl_async_signals() enabled. This is the recommended method
Setting tick frequency
Manual dispatch with pcntl_signal_dispatch()

When signals are dispatched asynchronously or using tick-based execution, blocking functions like sleep() may be interrupted.

pcntl_signal