21.queues.md

Queues

A queue is a sequence of callables that will always execute in a FIFO (First In First Out) order.

Each queue is identified by a unique tag, a name.

Queues can overlap while executing, but callables within the queues themselves will never overlap.

The QueueService provides 2 methods, queue() and consume()

/**
 * Queue a callable to run on a specific queue.
 * @param  string                   $tag the name of the queue.
 *                                  If it doesn't exist it will be created automatically.
 *
 * @param  callable                 $action callable to execute
 * @throws InvalidArgumentException
 * @return void
 */
public function queue($tag, $action);

/**
 * Consume all available callables on all queues.
 * Will not execute a second time unless the previous execution has finished.
 * @return void
 */
public function consume();

Tagging

Two callables that are delayed by 5 and 2 seconds using different tags tag-a and tag-b.

<?php
use CatPaw\Queue\Services\QueueService;
use function Amp\delay;

function main(QueueService $queue): void {
   $start = time();

   $queue->queue("tag-a", function() {
       delay(5000);
       echo 'a'.PHP_EOL;
   });

   $queue->queue("tag-b", function() {
       delay(2000);
       echo 'b'.PHP_EOL;
   });

   $queue->consume();

   $finish = time();
   $delta  = $finish - $start;
   echo "$delta seconds have passed.".PHP_EOL;
}

Output

b
a
5 seconds have passed.

Tagging the same identifier twice

Two callables that are delayed by 5 and 2 seconds both using the same tag my-tag.

<?php
use CatPaw\Queue\Services\QueueService;
use function Amp\delay;

function main(QueueService $queue): void {
    $start = time();

    $queue->queue("my-tag", function() {
        delay(5000);
        echo 'a'.PHP_EOL;
    });

    $queue->queue("my-tag", function() {
        delay(2000);
        echo 'b'.PHP_EOL;
    });

    $queue->consume();

    $finish = time();
    $delta  = $finish - $start;
    echo "$delta seconds have passed.".PHP_EOL;
}

Output

a
b
7 seconds have passed.