Icicle\Concurrent\Sync\PosixSemaphore::acquire PHP Method

    public function acquire() : \Generator
    {
        do {
            // Attempt to acquire a lock from the semaphore.
            if (@msg_receive($this->queue, 0, $type, 1, $chr, false, MSG_IPC_NOWAIT, $errno)) {
                // A free lock was found, so resolve with a lock object that can
                // be used to release the lock.
                return new Lock(function (Lock $lock) {
                    $this->release();
                });
            }
            // Check for unusual errors.
            if ($errno !== MSG_ENOMSG) {
                throw new SemaphoreException('Failed to acquire a lock.');
            }
        } while (yield from Coroutine\sleep(self::LATENCY_TIMEOUT));
    }