pcntl_alarm

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

pcntl_alarm — 为进程设置一个alarm闹钟信号

说明

pcntl_alarm(int $seconds): int

创建一个计时器，在指定的秒数后向进程发送一个SIGALRM信号。每次对 pcntl_alarm()的调用都会取消之前设置的alarm信号。

参数

seconds: 等待的秒数。如果seconds设置为0,将不会创建alarm信号。

返回值

返回上次alarm调度（离alarm信号发送）剩余的秒数，或者之前没有alarm调度（译注：或者之前调度已完成）时返回0。

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User Contributed Notes 3 notes

down

kuba at valentine dot dev ¶

1 year 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.


<?php

/**

 * Because we shouldn't handle asynchronous

 * events in synchronous manner.

 */

pcntl_async_signals(TRUE);


/**

 * 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.

 */

pcntl_alarm(2);


/**

 * 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)));

echo 'STATUS: '. $status . PHP_EOL;

down

molsavsky1 at gmail dot com ¶

6 months ago


Beware that pcntl_signal will interrupt (u)sleep calls which will not be resumed once the handler is completed.

It's a documented behaviour (https://www.php.net/manual/en/function.sleep.php) although it may look like a bug when encountered for the first time.

From the docs:
"If the call was interrupted by a signal, sleep() returns a non-zero value. On Windows, this value will always be 192 (the value of the WAIT_IO_COMPLETION constant within the Windows API). On other platforms, the return value will be the number of seconds left to sleep."

```
<?php

$interval = 1;
pcntl_async_signals(true);

pcntl_signal(SIGALRM, function () use ($interval): void {
    echo 'SIGALRM called' . PHP_EOL;
    pcntl_alarm($interval);
});

pcntl_alarm($interval);

echo 'Sleep (will be interrupted) started' . PHP_EOL;

sleep(100000000000);

echo 'Sleep ended soon due to interrupt' . PHP_EOL;

$sleepTimeout = 10;
echo "Proper sleep for {$sleepTimeout} seconds" . PHP_EOL;

$startedAt = time();
while ($sleepTimeout > 0 && ($sleepTimeout = sleep($sleepTimeout)) !== true) {
    echo "Sleep interrupted, {$sleepTimeout} seconds remaining" . PHP_EOL;
}

$elapsed = time() - $startedAt;
echo "Sleep finished after {$elapsed} seconds" . PHP_EOL;
```

down

-3

Gao,Shengwei ¶

4 years ago


Use pcntl_signal_dispatch() to catch the signal, don't use declare(ticks=1) because it is ineffcient

<?php
pcntl_signal(SIGALRM, function () {
    echo 'Received an alarm signal !' . PHP_EOL;
}, false);

pcntl_alarm(5);

while (true) {
    pcntl_signal_dispatch();
    sleep(1);
}

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官方地址：https://www.php.net/manual/en/function.pcntl-alarm.php

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pcntl_alarm

说明

参数

返回值

User Contributed Notes 3 notes