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。

User Contributed Notes

kuba at valentine dot dev 24-Oct-2020 08:25
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;
Gao,Shengwei 19-Apr-2018 05:12
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);
}