Watchdog timers

[danepowell]

I have a periodic timer that polls an external service every 5 seconds. When it sees a certain response it should cancel the timer and print the result.

But obviously I don't want that timer to run forever, so I've also created a watchdog timer that should cancel both timers after 45 minutes.

The problem is both timers need to be able to cancel each other, and it becomes a bootstrap problem. If I define it exactly as I've described above, the program will always run for 45 minutes because the pollingTimer has no way to reference the watchdogTimer.

Something like this, based on the example in the README:

$loop = React\EventLoop\Loop::get();

$timer = $loop->addPeriodicTimer(5, function () {
    if (someExternalResult()) {
      $loop->cancelTimer($timer);
      $loop->cancelTimer($watchdogTimer); // But $watchdogTimer isn't defined yet
    }
    echo 'Tick' . PHP_EOL;
});

$watchdogTimer = $loop->addTimer(60*45, function () use ($loop, $timer) {
    $loop->cancelTimer($timer);
    echo 'Done' . PHP_EOL;
});

$loop->run();

Am I missing something obvious here?

The workaround would be to have the pollingTimer just track the number of iterations it has run internally and cancel itself instead of relying on a watchdog. It's simpler in some ways but I'm not convinced it's 100% as effective.

[WyriHaximus]

Something like this?

$loop = React\EventLoop\Loop::get();

$timers = [];
$timers[] = $loop->addPeriodicTimer(5, function () use (&$timers) {
    if (someExternalResult()) {
      foreach ($timers as $timer) {
        $loop->cancelTimer($timer);
      }
      $timers = [];
    }
    echo 'Tick' . PHP_EOL;
});

$timers[] = $loop->addTimer(60*45, function () use ($loop, &$timers) {
    foreach ($timers as $timer) {
      $loop->cancelTimer($timer);
    }
    $timers = [];
    echo 'Done' . PHP_EOL;
});

$loop->run();

[danepowell]

That works perfectly, thanks! Of course now that you point it out it seems obvious 🙄 I'll open a PR to add it to the docs for the next person having a brain fart like me.

[WyriHaximus]

Looking forward to that PR, and while it's more a language thing, I do think it makes sense to add it as it's one of those tiny details that matter when using ReactPHP. I'll also close this issue as it has been answered :).