xref: /freebsd/sys/kern/subr_taskqueue.c (revision 8d20be1e22095c27faf8fe8b2f0d089739cc742e) 
1 /*-
2  * Copyright (c) 2000 Doug Rabson
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24  * SUCH DAMAGE.
25  */
26 
27 #include <sys/cdefs.h>
28 __FBSDID("$FreeBSD$");
29 
30 #include <sys/param.h>
31 #include <sys/systm.h>
32 #include <sys/bus.h>
33 #include <sys/interrupt.h>
34 #include <sys/kernel.h>
35 #include <sys/kthread.h>
36 #include <sys/limits.h>
37 #include <sys/lock.h>
38 #include <sys/malloc.h>
39 #include <sys/mutex.h>
40 #include <sys/proc.h>
41 #include <sys/sched.h>
42 #include <sys/taskqueue.h>
43 #include <sys/unistd.h>
44 #include <machine/stdarg.h>
45 
46 static MALLOC_DEFINE(M_TASKQUEUE, "taskqueue", "Task Queues");
47 static void	*taskqueue_giant_ih;
48 static void	*taskqueue_ih;
49 static void	 taskqueue_fast_enqueue(void *);
50 static void	 taskqueue_swi_enqueue(void *);
51 static void	 taskqueue_swi_giant_enqueue(void *);
52 
53 struct taskqueue_busy {
54 	struct task	*tb_running;
55 	TAILQ_ENTRY(taskqueue_busy) tb_link;
56 };
57 
58 struct taskqueue {
59 	STAILQ_HEAD(, task)	tq_queue;
60 	taskqueue_enqueue_fn	tq_enqueue;
61 	void			*tq_context;
62 	TAILQ_HEAD(, taskqueue_busy) tq_active;
63 	struct mtx		tq_mutex;
64 	struct thread		**tq_threads;
65 	int			tq_tcount;
66 	int			tq_spin;
67 	int			tq_flags;
68 	int			tq_callouts;
69 	taskqueue_callback_fn	tq_callbacks[TASKQUEUE_NUM_CALLBACKS];
70 	void			*tq_cb_contexts[TASKQUEUE_NUM_CALLBACKS];
71 };
72 
73 #define	TQ_FLAGS_ACTIVE		(1 << 0)
74 #define	TQ_FLAGS_BLOCKED	(1 << 1)
75 #define	TQ_FLAGS_UNLOCKED_ENQUEUE	(1 << 2)
76 
77 #define	DT_CALLOUT_ARMED	(1 << 0)
78 
79 #define	TQ_LOCK(tq)							\
80 	do {								\
81 		if ((tq)->tq_spin)					\
82 			mtx_lock_spin(&(tq)->tq_mutex);			\
83 		else							\
84 			mtx_lock(&(tq)->tq_mutex);			\
85 	} while (0)
86 #define	TQ_ASSERT_LOCKED(tq)	mtx_assert(&(tq)->tq_mutex, MA_OWNED)
87 
88 #define	TQ_UNLOCK(tq)							\
89 	do {								\
90 		if ((tq)->tq_spin)					\
91 			mtx_unlock_spin(&(tq)->tq_mutex);		\
92 		else							\
93 			mtx_unlock(&(tq)->tq_mutex);			\
94 	} while (0)
95 #define	TQ_ASSERT_UNLOCKED(tq)	mtx_assert(&(tq)->tq_mutex, MA_NOTOWNED)
96 
97 void
98 _timeout_task_init(struct taskqueue *queue, struct timeout_task *timeout_task,
99     int priority, task_fn_t func, void *context)
100 {
101 
102 	TASK_INIT(&timeout_task->t, priority, func, context);
103 	callout_init_mtx(&timeout_task->c, &queue->tq_mutex,
104 	    CALLOUT_RETURNUNLOCKED);
105 	timeout_task->q = queue;
106 	timeout_task->f = 0;
107 }
108 
109 static __inline int
110 TQ_SLEEP(struct taskqueue *tq, void *p, struct mtx *m, int pri, const char *wm,
111     int t)
112 {
113 	if (tq->tq_spin)
114 		return (msleep_spin(p, m, wm, t));
115 	return (msleep(p, m, pri, wm, t));
116 }
117 
118 static struct taskqueue *
119 _taskqueue_create(const char *name __unused, int mflags,
120 		 taskqueue_enqueue_fn enqueue, void *context,
121 		 int mtxflags, const char *mtxname)
122 {
123 	struct taskqueue *queue;
124 
125 	queue = malloc(sizeof(struct taskqueue), M_TASKQUEUE, mflags | M_ZERO);
126 	if (!queue)
127 		return NULL;
128 
129 	STAILQ_INIT(&queue->tq_queue);
130 	TAILQ_INIT(&queue->tq_active);
131 	queue->tq_enqueue = enqueue;
132 	queue->tq_context = context;
133 	queue->tq_spin = (mtxflags & MTX_SPIN) != 0;
134 	queue->tq_flags |= TQ_FLAGS_ACTIVE;
135 	if (enqueue == taskqueue_fast_enqueue ||
136 	    enqueue == taskqueue_swi_enqueue ||
137 	    enqueue == taskqueue_swi_giant_enqueue ||
138 	    enqueue == taskqueue_thread_enqueue)
139 		queue->tq_flags |= TQ_FLAGS_UNLOCKED_ENQUEUE;
140 	mtx_init(&queue->tq_mutex, mtxname, NULL, mtxflags);
141 
142 	return queue;
143 }
144 
145 struct taskqueue *
146 taskqueue_create(const char *name, int mflags,
147 		 taskqueue_enqueue_fn enqueue, void *context)
148 {
149 	return _taskqueue_create(name, mflags, enqueue, context,
150 			MTX_DEF, "taskqueue");
151 }
152 
153 void
154 taskqueue_set_callback(struct taskqueue *queue,
155     enum taskqueue_callback_type cb_type, taskqueue_callback_fn callback,
156     void *context)
157 {
158 
159 	KASSERT(((cb_type >= TASKQUEUE_CALLBACK_TYPE_MIN) &&
160 	    (cb_type <= TASKQUEUE_CALLBACK_TYPE_MAX)),
161 	    ("Callback type %d not valid, must be %d-%d", cb_type,
162 	    TASKQUEUE_CALLBACK_TYPE_MIN, TASKQUEUE_CALLBACK_TYPE_MAX));
163 	KASSERT((queue->tq_callbacks[cb_type] == NULL),
164 	    ("Re-initialization of taskqueue callback?"));
165 
166 	queue->tq_callbacks[cb_type] = callback;
167 	queue->tq_cb_contexts[cb_type] = context;
168 }
169 
170 /*
171  * Signal a taskqueue thread to terminate.
172  */
173 static void
174 taskqueue_terminate(struct thread **pp, struct taskqueue *tq)
175 {
176 
177 	while (tq->tq_tcount > 0 || tq->tq_callouts > 0) {
178 		wakeup(tq);
179 		TQ_SLEEP(tq, pp, &tq->tq_mutex, PWAIT, "taskqueue_destroy", 0);
180 	}
181 }
182 
183 void
184 taskqueue_free(struct taskqueue *queue)
185 {
186 
187 	TQ_LOCK(queue);
188 	queue->tq_flags &= ~TQ_FLAGS_ACTIVE;
189 	taskqueue_terminate(queue->tq_threads, queue);
190 	KASSERT(TAILQ_EMPTY(&queue->tq_active), ("Tasks still running?"));
191 	KASSERT(queue->tq_callouts == 0, ("Armed timeout tasks"));
192 	mtx_destroy(&queue->tq_mutex);
193 	free(queue->tq_threads, M_TASKQUEUE);
194 	free(queue, M_TASKQUEUE);
195 }
196 
197 static int
198 taskqueue_enqueue_locked(struct taskqueue *queue, struct task *task)
199 {
200 	struct task *ins;
201 	struct task *prev;
202 
203 	/*
204 	 * Count multiple enqueues.
205 	 */
206 	if (task->ta_pending) {
207 		if (task->ta_pending < USHRT_MAX)
208 			task->ta_pending++;
209 		TQ_UNLOCK(queue);
210 		return (0);
211 	}
212 
213 	/*
214 	 * Optimise the case when all tasks have the same priority.
215 	 */
216 	prev = STAILQ_LAST(&queue->tq_queue, task, ta_link);
217 	if (!prev || prev->ta_priority >= task->ta_priority) {
218 		STAILQ_INSERT_TAIL(&queue->tq_queue, task, ta_link);
219 	} else {
220 		prev = NULL;
221 		for (ins = STAILQ_FIRST(&queue->tq_queue); ins;
222 		     prev = ins, ins = STAILQ_NEXT(ins, ta_link))
223 			if (ins->ta_priority < task->ta_priority)
224 				break;
225 
226 		if (prev)
227 			STAILQ_INSERT_AFTER(&queue->tq_queue, prev, task, ta_link);
228 		else
229 			STAILQ_INSERT_HEAD(&queue->tq_queue, task, ta_link);
230 	}
231 
232 	task->ta_pending = 1;
233 	if ((queue->tq_flags & TQ_FLAGS_UNLOCKED_ENQUEUE) != 0)
234 		TQ_UNLOCK(queue);
235 	if ((queue->tq_flags & TQ_FLAGS_BLOCKED) == 0)
236 		queue->tq_enqueue(queue->tq_context);
237 	if ((queue->tq_flags & TQ_FLAGS_UNLOCKED_ENQUEUE) == 0)
238 		TQ_UNLOCK(queue);
239 
240 	/* Return with lock released. */
241 	return (0);
242 }
243 int
244 taskqueue_enqueue(struct taskqueue *queue, struct task *task)
245 {
246 	int res;
247 
248 	TQ_LOCK(queue);
249 	res = taskqueue_enqueue_locked(queue, task);
250 	/* The lock is released inside. */
251 
252 	return (res);
253 }
254 
255 static void
256 taskqueue_timeout_func(void *arg)
257 {
258 	struct taskqueue *queue;
259 	struct timeout_task *timeout_task;
260 
261 	timeout_task = arg;
262 	queue = timeout_task->q;
263 	KASSERT((timeout_task->f & DT_CALLOUT_ARMED) != 0, ("Stray timeout"));
264 	timeout_task->f &= ~DT_CALLOUT_ARMED;
265 	queue->tq_callouts--;
266 	taskqueue_enqueue_locked(timeout_task->q, &timeout_task->t);
267 	/* The lock is released inside. */
268 }
269 
270 int
271 taskqueue_enqueue_timeout(struct taskqueue *queue,
272     struct timeout_task *timeout_task, int ticks)
273 {
274 	int res;
275 
276 	TQ_LOCK(queue);
277 	KASSERT(timeout_task->q == NULL || timeout_task->q == queue,
278 	    ("Migrated queue"));
279 	KASSERT(!queue->tq_spin, ("Timeout for spin-queue"));
280 	timeout_task->q = queue;
281 	res = timeout_task->t.ta_pending;
282 	if (ticks == 0) {
283 		taskqueue_enqueue_locked(queue, &timeout_task->t);
284 		/* The lock is released inside. */
285 	} else {
286 		if ((timeout_task->f & DT_CALLOUT_ARMED) != 0) {
287 			res++;
288 		} else {
289 			queue->tq_callouts++;
290 			timeout_task->f |= DT_CALLOUT_ARMED;
291 			if (ticks < 0)
292 				ticks = -ticks; /* Ignore overflow. */
293 		}
294 		if (ticks > 0) {
295 			callout_reset(&timeout_task->c, ticks,
296 			    taskqueue_timeout_func, timeout_task);
297 		}
298 		TQ_UNLOCK(queue);
299 	}
300 	return (res);
301 }
302 
303 void
304 taskqueue_block(struct taskqueue *queue)
305 {
306 
307 	TQ_LOCK(queue);
308 	queue->tq_flags |= TQ_FLAGS_BLOCKED;
309 	TQ_UNLOCK(queue);
310 }
311 
312 void
313 taskqueue_unblock(struct taskqueue *queue)
314 {
315 
316 	TQ_LOCK(queue);
317 	queue->tq_flags &= ~TQ_FLAGS_BLOCKED;
318 	if (!STAILQ_EMPTY(&queue->tq_queue))
319 		queue->tq_enqueue(queue->tq_context);
320 	TQ_UNLOCK(queue);
321 }
322 
323 static void
324 taskqueue_run_locked(struct taskqueue *queue)
325 {
326 	struct taskqueue_busy tb;
327 	struct task *task;
328 	int pending;
329 
330 	TQ_ASSERT_LOCKED(queue);
331 	tb.tb_running = NULL;
332 	TAILQ_INSERT_TAIL(&queue->tq_active, &tb, tb_link);
333 
334 	while (STAILQ_FIRST(&queue->tq_queue)) {
335 		/*
336 		 * Carefully remove the first task from the queue and
337 		 * zero its pending count.
338 		 */
339 		task = STAILQ_FIRST(&queue->tq_queue);
340 		STAILQ_REMOVE_HEAD(&queue->tq_queue, ta_link);
341 		pending = task->ta_pending;
342 		task->ta_pending = 0;
343 		tb.tb_running = task;
344 		TQ_UNLOCK(queue);
345 
346 		task->ta_func(task->ta_context, pending);
347 
348 		TQ_LOCK(queue);
349 		tb.tb_running = NULL;
350 		wakeup(task);
351 	}
352 	TAILQ_REMOVE(&queue->tq_active, &tb, tb_link);
353 }
354 
355 void
356 taskqueue_run(struct taskqueue *queue)
357 {
358 
359 	TQ_LOCK(queue);
360 	taskqueue_run_locked(queue);
361 	TQ_UNLOCK(queue);
362 }
363 
364 static int
365 task_is_running(struct taskqueue *queue, struct task *task)
366 {
367 	struct taskqueue_busy *tb;
368 
369 	TQ_ASSERT_LOCKED(queue);
370 	TAILQ_FOREACH(tb, &queue->tq_active, tb_link) {
371 		if (tb->tb_running == task)
372 			return (1);
373 	}
374 	return (0);
375 }
376 
377 static int
378 taskqueue_cancel_locked(struct taskqueue *queue, struct task *task,
379     u_int *pendp)
380 {
381 
382 	if (task->ta_pending > 0)
383 		STAILQ_REMOVE(&queue->tq_queue, task, task, ta_link);
384 	if (pendp != NULL)
385 		*pendp = task->ta_pending;
386 	task->ta_pending = 0;
387 	return (task_is_running(queue, task) ? EBUSY : 0);
388 }
389 
390 int
391 taskqueue_cancel(struct taskqueue *queue, struct task *task, u_int *pendp)
392 {
393 	u_int pending;
394 	int error;
395 
396 	TQ_LOCK(queue);
397 	pending = task->ta_pending;
398 	error = taskqueue_cancel_locked(queue, task, pendp);
399 	TQ_UNLOCK(queue);
400 
401 	return (error);
402 }
403 
404 int
405 taskqueue_cancel_timeout(struct taskqueue *queue,
406     struct timeout_task *timeout_task, u_int *pendp)
407 {
408 	u_int pending, pending1;
409 	int error;
410 
411 	TQ_LOCK(queue);
412 	pending = !!callout_stop(&timeout_task->c);
413 	error = taskqueue_cancel_locked(queue, &timeout_task->t, &pending1);
414 	if ((timeout_task->f & DT_CALLOUT_ARMED) != 0) {
415 		timeout_task->f &= ~DT_CALLOUT_ARMED;
416 		queue->tq_callouts--;
417 	}
418 	TQ_UNLOCK(queue);
419 
420 	if (pendp != NULL)
421 		*pendp = pending + pending1;
422 	return (error);
423 }
424 
425 void
426 taskqueue_drain(struct taskqueue *queue, struct task *task)
427 {
428 
429 	if (!queue->tq_spin)
430 		WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
431 
432 	TQ_LOCK(queue);
433 	while (task->ta_pending != 0 || task_is_running(queue, task))
434 		TQ_SLEEP(queue, task, &queue->tq_mutex, PWAIT, "-", 0);
435 	TQ_UNLOCK(queue);
436 }
437 
438 void
439 taskqueue_drain_timeout(struct taskqueue *queue,
440     struct timeout_task *timeout_task)
441 {
442 
443 	callout_drain(&timeout_task->c);
444 	taskqueue_drain(queue, &timeout_task->t);
445 }
446 
447 static void
448 taskqueue_swi_enqueue(void *context)
449 {
450 	swi_sched(taskqueue_ih, 0);
451 }
452 
453 static void
454 taskqueue_swi_run(void *dummy)
455 {
456 	taskqueue_run(taskqueue_swi);
457 }
458 
459 static void
460 taskqueue_swi_giant_enqueue(void *context)
461 {
462 	swi_sched(taskqueue_giant_ih, 0);
463 }
464 
465 static void
466 taskqueue_swi_giant_run(void *dummy)
467 {
468 	taskqueue_run(taskqueue_swi_giant);
469 }
470 
471 int
472 taskqueue_start_threads(struct taskqueue **tqp, int count, int pri,
473 			const char *name, ...)
474 {
475 	va_list ap;
476 	struct thread *td;
477 	struct taskqueue *tq;
478 	int i, error;
479 	char ktname[MAXCOMLEN + 1];
480 
481 	if (count <= 0)
482 		return (EINVAL);
483 
484 	tq = *tqp;
485 
486 	va_start(ap, name);
487 	vsnprintf(ktname, sizeof(ktname), name, ap);
488 	va_end(ap);
489 
490 	tq->tq_threads = malloc(sizeof(struct thread *) * count, M_TASKQUEUE,
491 	    M_NOWAIT | M_ZERO);
492 	if (tq->tq_threads == NULL) {
493 		printf("%s: no memory for %s threads\n", __func__, ktname);
494 		return (ENOMEM);
495 	}
496 
497 	for (i = 0; i < count; i++) {
498 		if (count == 1)
499 			error = kthread_add(taskqueue_thread_loop, tqp, NULL,
500 			    &tq->tq_threads[i], RFSTOPPED, 0, "%s", ktname);
501 		else
502 			error = kthread_add(taskqueue_thread_loop, tqp, NULL,
503 			    &tq->tq_threads[i], RFSTOPPED, 0,
504 			    "%s_%d", ktname, i);
505 		if (error) {
506 			/* should be ok to continue, taskqueue_free will dtrt */
507 			printf("%s: kthread_add(%s): error %d", __func__,
508 			    ktname, error);
509 			tq->tq_threads[i] = NULL;		/* paranoid */
510 		} else
511 			tq->tq_tcount++;
512 	}
513 	for (i = 0; i < count; i++) {
514 		if (tq->tq_threads[i] == NULL)
515 			continue;
516 		td = tq->tq_threads[i];
517 		thread_lock(td);
518 		sched_prio(td, pri);
519 		sched_add(td, SRQ_BORING);
520 		thread_unlock(td);
521 	}
522 
523 	return (0);
524 }
525 
526 static inline void
527 taskqueue_run_callback(struct taskqueue *tq,
528     enum taskqueue_callback_type cb_type)
529 {
530 	taskqueue_callback_fn tq_callback;
531 
532 	TQ_ASSERT_UNLOCKED(tq);
533 	tq_callback = tq->tq_callbacks[cb_type];
534 	if (tq_callback != NULL)
535 		tq_callback(tq->tq_cb_contexts[cb_type]);
536 }
537 
538 void
539 taskqueue_thread_loop(void *arg)
540 {
541 	struct taskqueue **tqp, *tq;
542 
543 	tqp = arg;
544 	tq = *tqp;
545 	taskqueue_run_callback(tq, TASKQUEUE_CALLBACK_TYPE_INIT);
546 	TQ_LOCK(tq);
547 	while ((tq->tq_flags & TQ_FLAGS_ACTIVE) != 0) {
548 		taskqueue_run_locked(tq);
549 		/*
550 		 * Because taskqueue_run() can drop tq_mutex, we need to
551 		 * check if the TQ_FLAGS_ACTIVE flag wasn't removed in the
552 		 * meantime, which means we missed a wakeup.
553 		 */
554 		if ((tq->tq_flags & TQ_FLAGS_ACTIVE) == 0)
555 			break;
556 		TQ_SLEEP(tq, tq, &tq->tq_mutex, 0, "-", 0);
557 	}
558 	taskqueue_run_locked(tq);
559 
560 	/*
561 	 * This thread is on its way out, so just drop the lock temporarily
562 	 * in order to call the shutdown callback.  This allows the callback
563 	 * to look at the taskqueue, even just before it dies.
564 	 */
565 	TQ_UNLOCK(tq);
566 	taskqueue_run_callback(tq, TASKQUEUE_CALLBACK_TYPE_SHUTDOWN);
567 	TQ_LOCK(tq);
568 
569 	/* rendezvous with thread that asked us to terminate */
570 	tq->tq_tcount--;
571 	wakeup_one(tq->tq_threads);
572 	TQ_UNLOCK(tq);
573 	kthread_exit();
574 }
575 
576 void
577 taskqueue_thread_enqueue(void *context)
578 {
579 	struct taskqueue **tqp, *tq;
580 
581 	tqp = context;
582 	tq = *tqp;
583 
584 	wakeup_one(tq);
585 }
586 
587 TASKQUEUE_DEFINE(swi, taskqueue_swi_enqueue, NULL,
588 		 swi_add(NULL, "task queue", taskqueue_swi_run, NULL, SWI_TQ,
589 		     INTR_MPSAFE, &taskqueue_ih));
590 
591 TASKQUEUE_DEFINE(swi_giant, taskqueue_swi_giant_enqueue, NULL,
592 		 swi_add(NULL, "Giant taskq", taskqueue_swi_giant_run,
593 		     NULL, SWI_TQ_GIANT, 0, &taskqueue_giant_ih));
594 
595 TASKQUEUE_DEFINE_THREAD(thread);
596 
597 struct taskqueue *
598 taskqueue_create_fast(const char *name, int mflags,
599 		 taskqueue_enqueue_fn enqueue, void *context)
600 {
601 	return _taskqueue_create(name, mflags, enqueue, context,
602 			MTX_SPIN, "fast_taskqueue");
603 }
604 
605 /* NB: for backwards compatibility */
606 int
607 taskqueue_enqueue_fast(struct taskqueue *queue, struct task *task)
608 {
609 	return taskqueue_enqueue(queue, task);
610 }
611 
612 static void	*taskqueue_fast_ih;
613 
614 static void
615 taskqueue_fast_enqueue(void *context)
616 {
617 	swi_sched(taskqueue_fast_ih, 0);
618 }
619 
620 static void
621 taskqueue_fast_run(void *dummy)
622 {
623 	taskqueue_run(taskqueue_fast);
624 }
625 
626 TASKQUEUE_FAST_DEFINE(fast, taskqueue_fast_enqueue, NULL,
627 	swi_add(NULL, "fast taskq", taskqueue_fast_run, NULL,
628 	SWI_TQ_FAST, INTR_MPSAFE, &taskqueue_fast_ih));
629 
630 int
631 taskqueue_member(struct taskqueue *queue, struct thread *td)
632 {
633 	int i, j, ret = 0;
634 
635 	for (i = 0, j = 0; ; i++) {
636 		if (queue->tq_threads[i] == NULL)
637 			continue;
638 		if (queue->tq_threads[i] == td) {
639 			ret = 1;
640 			break;
641 		}
642 		if (++j >= queue->tq_tcount)
643 			break;
644 	}
645 	return (ret);
646 }
647