Timers

Timers are the objects the loop watches. Each timer keeps a queue of trigger times, and each time a timer is due it runs every callback attached to it.

IndividualTimer

IndividualTimer is for one-off trigger times.

We can schedule a relative delay in the constructor:

use GT\Async\Timer\IndividualTimer;

$timer = new IndividualTimer(5);

That means "trigger once, five seconds from now".

We can also add absolute trigger times:

$start = microtime(true);

$timer = new IndividualTimer();
$timer->addTriggerTime($start + 1);
$timer->addTriggerTime($start + 5);
$timer->addTriggerTime($start + 10);

addTriggerTime() expects a Unix epoch float, not a delay value.

PeriodicTimer

PeriodicTimer is for repeated work at a fixed interval.

use Gt\Async\Timer\PeriodicTimer;

$timer = new PeriodicTimer(0.25, true);

This timer will trigger every quarter of a second, and because the second argument is true, the first tick is immediate.

If we want the timer to wait before the first tick, use:

$timer = new PeriodicTimer(0.25, false);

Adding and removing callbacks

Any timer can hold more than one callback:

$timer->addCallback(function() {
	echo "A", PHP_EOL;
});

$timer->addCallback(function() {
	echo "B", PHP_EOL;
});

When the timer ticks, both callbacks run in the order they were added.

Callbacks can also be removed:

$callback = function() {
	echo "Only once", PHP_EOL;
};

$timer->addCallback($callback);
$timer->removeCallback($callback);

Running several timers together

The loop can observe any number of timers at once.

use GT\Async\Loop;
use GT\Async\Timer\IndividualTimer;
use GT\Async\Timer\PeriodicTimer;

$loop = new Loop();
$stopTimer = new IndividualTimer(5);
$countdownTimer = new PeriodicTimer(1, true);
$dotTimer = new PeriodicTimer(0.1, true);
$count = 5;

$countdownTimer->addCallback(function() use(&$count) {
	echo "Countdown: $count", PHP_EOL;
	$count--;
});

$dotTimer->addCallback(function() {
	echo ".";
});

$stopTimer->addCallback(function() use($loop) {
	echo PHP_EOL, "Stop", PHP_EOL;
	$loop->halt();
});

$loop->addTimer($countdownTimer);
$loop->addTimer($dotTimer);
$loop->addTimer($stopTimer);
$loop->run();

This is the main idea behind the package: small pieces of work can take turns without us having to block on one long operation.

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Next, move on to Deferred work to connect the loop to Deferred objects and promises.