signal ​

(PHP 8.6+, True Async 1.0)

signal() — Waits for an OS signal. Returns a Future that resolves with a Signal value when the signal is received.

Description ​

signal(Async\Signal $signal, ?Async\Completable $cancellation = null): Async\Future

Creates a one-shot OS signal handler. Each call to signal() creates a new Future that resolves upon the first receipt of the specified signal. If the $cancellation parameter is provided, the Future will be rejected when the cancellation triggers (e.g., on timeout).

Multiple calls to signal() with the same signal work independently — each will receive a notification.

Parameters ​

signal An Async\Signal enum value specifying the expected signal. For example: Signal::SIGINT, Signal::SIGTERM, Signal::SIGUSR1.

cancellation An optional object implementing Async\Completable (e.g., a result of calling timeout()). If the cancellation object triggers before the signal arrives, the Future will be rejected with the corresponding exception (e.g., Async\TimeoutException).

If the cancellation object has already completed at the time of the call, signal() immediately returns a rejected Future.

Return Values ​

Returns Async\Future<Async\Signal>. When the signal is received, the Future resolves with the Async\Signal enum value corresponding to the received signal.

Errors/Exceptions ​

• Async\OperationCanceledException — if the cancellation token triggered (including timeout). The original exception from the token is available via $e->getPrevious() (e.g., TimeoutException when using timeout()).

Examples ​

Example #1 Waiting for a signal with timeout ​

<?php
use Async\Signal;
use function Async\signal;
use function Async\timeout;
use function Async\await;

try {
    $result = await(signal(Signal::SIGINT, timeout(5000)));
    echo "Signal received: " . $result->name . "\n";
} catch (Async\OperationCanceledException $e) {
    echo "Signal not received within 5 seconds\n";
}
?>

Example #2 Receiving a signal from another coroutine ​

<?php
use Async\Signal;
use function Async\signal;
use function Async\await;
use function Async\spawn;

$future = signal(Signal::SIGUSR1);

spawn(function() {
    posix_kill(getmypid(), SIGUSR1);
});

$result = await($future);
echo "Signal received: " . $result->name . "\n";
var_dump($result === Signal::SIGUSR1); // bool(true)
?>

Example #3 Graceful shutdown on SIGTERM ​

<?php
use Async\Signal;
use function Async\signal;
use function Async\await;
use function Async\spawn;
use function Async\graceful_shutdown;

spawn(function() {
    await(signal(Signal::SIGTERM));
    echo "SIGTERM received, shutting down...\n";
    graceful_shutdown();
});
?>

Example #4 Already expired timeout ​

<?php
use Async\Signal;
use function Async\signal;
use function Async\timeout;
use function Async\await;
use function Async\delay;

$t = timeout(1);
delay(50); // Timeout has already expired

$future = signal(Signal::SIGINT, $t);

try {
    await($future);
} catch (Async\OperationCanceledException $e) {
    echo get_class($e) . "\n"; // Async\OperationCanceledException
    echo get_class($e->getPrevious()) . "\n"; // Async\TimeoutException
}
?>

Notes ​

Note: Each call to signal() creates a one-shot handler. To wait for the same signal again, call signal() again.

Note: Signal::SIGINT and Signal::SIGBREAK work on all platforms, including Windows. Signals SIGUSR1, SIGUSR2, and other POSIX signals are only available on Unix systems.

Note: Signal::SIGKILL and Signal::SIGSEGV cannot be caught — this is an operating system limitation.

Signal ​

The Async\Signal enum defines the available OS signals:

See Also ​

• timeout() — create a timeout to limit waiting
• await() — waiting for a Future result
• graceful_shutdown() — graceful scheduler shutdown
• Cancellation — cancellation mechanism