PHP: pcntl_signal

Description

function 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:

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

signo: 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:
When a handler is set to an object method, the reference count of that object is increased, which makes it persist until the handler is changed to something else, or the script ends.

restart_syscalls

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

Note:
Although this parameter defaults to true, that default does not apply to SIGALRM: when restart_syscalls is not passed and signal is SIGALRM, system call restarting is disabled. Pass true explicitly to enable system call restarting for SIGALRM.

Return Values

Returns true on success or false on failure.

Errors/Exceptions

A ValueError is thrown if signal is less than 1 or greater than or equal to NSIG, or if handler is an int other than SIG_DFL or SIG_IGN.

A TypeError is thrown if handler is neither a callable nor an int.

Changelog

Version	Description
7.4.0	`restart_syscalls` is now honoured for `SIGALRM`; previously system call restarting was always disabled for that signal. When the argument is not passed, system call restarting remains disabled for `SIGALRM`.
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() does not 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