Function gtaskqueue_drain_tq_queue

freebsd/kern/subr_gtaskqueue.c:261–287

* Block until all currently queued tasks in this taskqueue * have begun execution. Tasks queued during execution of * this function are ignored. */

 * this function are ignored.
 */
static void
gtaskqueue_drain_tq_queue(struct gtaskqueue *queue)
{
	struct gtask t_barrier;

	if (STAILQ_EMPTY(&queue->tq_queue))
		return;

	/*
	 * Enqueue our barrier after all current tasks, but with
	 * the highest priority so that newly queued tasks cannot
	 * pass it.  Because of the high priority, we can not use
	 * taskqueue_enqueue_locked directly (which drops the lock
	 * anyway) so just insert it at tail while we have the
	 * queue lock.
	 */
	GTASK_INIT(&t_barrier, 0, USHRT_MAX, gtaskqueue_task_nop_fn, &t_barrier);
	STAILQ_INSERT_TAIL(&queue->tq_queue, &t_barrier, ta_link);
	t_barrier.ta_flags |= TASK_ENQUEUED;

	/*
	 * Once the barrier has executed, all previously queued tasks
	 * have completed or are currently executing.
	 */
	while (t_barrier.ta_flags & TASK_ENQUEUED)
		TQ_SLEEP(queue, &t_barrier, "gtq_qdrain");
}

/*
 * Block until all currently executing tasks for this taskqueue