Question

I’m having some difficulties getting the PHP libevent extension to break out of a loop on a timeout. Here’s what I’ve got so far based on the demos on the PHP.net docs pages:

// From here: http://www.php.net/manual/en/libevent.examples.php

function print_line($fd, $events, $arg) {
    static $max_requests = 0;
    $max_requests++;

    printf("Received event: %s after %s\n%s", implode(getEventFlags($events)), getTimer(), fgets($fd));

    if ($max_requests == 10) {
        // exit loop after 3 writes
        echo " [EXIT]\n";
        event_base_loopexit($arg[1]);
    }
}

// create base and event
$base = event_base_new();
$event = event_new();


getTimer(); // Initialise time

$fd = STDIN;
event_set($event, $fd, EV_READ | EV_PERSIST, "print_line", array($event, $base));
event_base_set($event, $base);
event_add($event, 2000000);
event_base_loop($base);

// extract flags from bitmask
function getEventFlags ($ebm) {
    $expFlags = array('EV_TIMEOUT', 'EV_SIGNAL', 'EV_READ', 'EV_WRITE', 'EV_PERSIST');
    $ret = array();
    foreach ($expFlags as $exf) {
        if ($ebm & constant($exf)) {
            $ret[] = $exf;
        }
    }
    return $ret;
}

// Used to track time!
function getTimer () {
    static $ts;
    if (is_null($ts)) {
        $ts = microtime(true);
        return "Timer initialised";
    }
    $newts = microtime(true);
    $r = sprintf("Delta: %.3f", $newts - $ts);
    $ts = $newts;
    return $r;
}

I can see that the timeout value passed to event_add effects the events passed to print_line(), if these events are any more than 2 seconds apart I get an EV_TIMEOUT instead of an EV_READ. What I want however is for libevent to call print_line as soon as the timeout is reached rather than waiting for the next event in order to give me the timeout.

I’ve tried using event_base_loopexit($base, 2000000), this causes the event loop to exit immediately without blocking for events. I’ve also tried passing EV_TIMEOUT to event_set, this seems to have no effect at all.

Has anyone managed to get this working before? I know that the event_buffer_* stuff works with timeouts, however I want to use the standard event_base functions. One of the PECL bugs talks about event_timer_* functions and these functions do exist on my system, however they’re not documented at all.

Answer 1

Problem is in fgets() in:

printf("Received event: %s after %s\n%s", implode(getEventFlags($events)), getTimer(), fgets($fd));

This blocks processing and waits for data from STDIN (but there are none on timeout)

Change to something like that:

$text = '';
if ($events & EV_READ) {
    $text = fgets($fd);
}
printf("Received event: %s after %s\n%s", implode(getEventFlags($events)), getTimer(), $text);