concurrent-requests.php

<?php

require __DIR__ . '/vendor/autoload.php';

use Amp\Loop;
use Amp\Artax;

$queue = new SplQueue;
$waiting = new Amp\Deferred;
$http = new Artax\DefaultClient;

$worker = Amp\coroutine(function ($workerId) use ($queue, &$waiting, $http) {
    while (true) {
        while ($queue->isEmpty()) {
            yield $waiting->promise();
        }

        $uri = $queue->pop();
        $response = yield $http->request($uri);
        $responseBody = yield $response->getBody();

        print "#" . $workerId . " - " . $uri . " → " . $response->getStatus() . " " . $response->getReason() . " (queue size: " . $queue->count() . ")" . PHP_EOL;

        if (random_int(0, 1) === 1) {
            $isEmpty = $queue->isEmpty();

            $queue->push("http://example.com/" . random_int(0, 32));
            $queue->push("http://example.net/" . random_int(0, 32));

            if ($isEmpty) {
                $deferred = $waiting;
                $waiting = new Amp\Deferred;
                $deferred->resolve();
            }
        }
    }
});

$queue->push("http://example.com/");

Loop::run(function () use ($worker) {
    // Create workers and wait for them to finish
    yield array_map($worker, range(0, 3));

    // Because we automatically exit the event loop, this line will never be reached.
    // If some end condition is known, the while (true) in the workers can be replaced
    // and then this line will be reached once finished.
    print "Finished processing." . PHP_EOL; // <-- Never reached
});