name : TaskQueueInterface.php <?php declare(strict_types=1); namespace GuzzleHttp\Promise; interface TaskQueueInterface { /** * Returns true if the queue is empty. */ public function isEmpty(): bool; /** * Adds a task to the queue that will be executed the next time run is * called. */ public function add(callable $task): void; /** * Execute all of the pending task in the queue. */ public function run(): void; }