Function sleepq_add

freebsd/kern/subr_sleepqueue.c:308–388

* Places the current thread on the sleep queue for the specified wait * channel. If INVARIANTS is enabled, then it associates the passed in * lock with the sleepq to make sure it is held when that sleep queue is * woken up. */

 * woken up.
 */
void
sleepq_add(const void *wchan, struct lock_object *lock, const char *wmesg,
    int flags, int queue)
{
	struct sleepqueue_chain *sc;
	struct sleepqueue *sq;
	struct thread *td;

	td = curthread;
	sc = SC_LOOKUP(wchan);
	mtx_assert(&sc->sc_lock, MA_OWNED);
	MPASS(td->td_sleepqueue != NULL);
	MPASS(wchan != NULL);
	MPASS((queue >= 0) && (queue < NR_SLEEPQS));

	/* If this thread is not allowed to sleep, die a horrible death. */
	if (__predict_false(!THREAD_CAN_SLEEP())) {
#ifdef EPOCH_TRACE
		epoch_trace_list(curthread);
#endif
		KASSERT(0,
		    ("%s: td %p to sleep on wchan %p with sleeping prohibited",
		    __func__, td, wchan));
	}

	/* Look up the sleep queue associated with the wait channel 'wchan'. */
	sq = sleepq_lookup(wchan);

	/*
	 * If the wait channel does not already have a sleep queue, use
	 * this thread's sleep queue.  Otherwise, insert the current thread
	 * into the sleep queue already in use by this wait channel.
	 */
	if (sq == NULL) {
#ifdef INVARIANTS
		int i;

		sq = td->td_sleepqueue;
		for (i = 0; i < NR_SLEEPQS; i++) {
			KASSERT(TAILQ_EMPTY(&sq->sq_blocked[i]),
			    ("thread's sleep queue %d is not empty", i));
			KASSERT(sq->sq_blockedcnt[i] == 0,
			    ("thread's sleep queue %d count mismatches", i));
		}
		KASSERT(LIST_EMPTY(&sq->sq_free),
		    ("thread's sleep queue has a non-empty free list"));
		KASSERT(sq->sq_wchan == NULL, ("stale sq_wchan pointer"));
		sq->sq_lock = lock;
#endif
#ifdef SLEEPQUEUE_PROFILING
		sc->sc_depth++;
		if (sc->sc_depth > sc->sc_max_depth) {
			sc->sc_max_depth = sc->sc_depth;
			if (sc->sc_max_depth > sleepq_max_depth)
				sleepq_max_depth = sc->sc_max_depth;
		}
#endif
		sq = td->td_sleepqueue;