lib/isc/rwlock.c

34 #define VALID_RWLOCK(rwl)	ISC_MAGIC_VALID(rwl, RWLOCK_MAGIC)
51 print_lock(const char *operation, isc_rwlock_t *rwl, isc_rwlocktype_t type) {
57 		rwl, isc_thread_self(), operation,
63 		(rwl->type == isc_rwlocktype_read ?
68 		rwl->active, rwl->granted, rwl->readers_waiting,
69 		rwl->writers_waiting);
74 isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
79 	REQUIRE(rwl != NULL);
85 	rwl->magic = 0;
88 	rwl->write_requests = 0;
89 	rwl->write_completions = 0;
90 	rwl->cnt_and_flag = 0;
91 	rwl->readers_waiting = 0;
92 	rwl->write_granted = 0;
99 	rwl->write_quota = write_quota;
101 	rwl->type = isc_rwlocktype_read;
102 	rwl->original = isc_rwlocktype_none;
103 	rwl->active = 0;
104 	rwl->granted = 0;
105 	rwl->readers_waiting = 0;
106 	rwl->writers_waiting = 0;
109 	rwl->read_quota = read_quota;
112 	rwl->write_quota = write_quota;
115 	result = isc_mutex_init(&rwl->lock);
119 	result = isc_condition_init(&rwl->readable);
129 	result = isc_condition_init(&rwl->writeable);
140 	rwl->magic = RWLOCK_MAGIC;
145 	(void)isc_condition_destroy(&rwl->readable);
147 	DESTROYLOCK(&rwl->lock);
153 isc_rwlock_destroy(isc_rwlock_t *rwl) {
154 	REQUIRE(VALID_RWLOCK(rwl));
157 	REQUIRE(rwl->write_requests == rwl->write_completions &&
158 		rwl->cnt_and_flag == 0 && rwl->readers_waiting == 0);
160 	LOCK(&rwl->lock);
161 	REQUIRE(rwl->active == 0 &&
162 		rwl->readers_waiting == 0 &&
163 		rwl->writers_waiting == 0);
164 	UNLOCK(&rwl->lock);
167 	rwl->magic = 0;
168 	(void)isc_condition_destroy(&rwl->readable);
169 	(void)isc_condition_destroy(&rwl->writeable);
170 	DESTROYLOCK(&rwl->lock);
241 isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
244 	REQUIRE(VALID_RWLOCK(rwl));
248 				  ISC_MSG_PRELOCK, "prelock"), rwl, type);
252 		if (rwl->write_requests != rwl->write_completions) {
254 			LOCK(&rwl->lock);
255 			if (rwl->write_requests != rwl->write_completions) {
256 				rwl->readers_waiting++;
257 				WAIT(&rwl->readable, &rwl->lock);
258 				rwl->readers_waiting--;
260 			UNLOCK(&rwl->lock);
263 		cntflag = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
266 			if ((rwl->cnt_and_flag & WRITER_ACTIVE) == 0)
270 			LOCK(&rwl->lock);
271 			rwl->readers_waiting++;
272 			if ((rwl->cnt_and_flag & WRITER_ACTIVE) != 0)
273 				WAIT(&rwl->readable, &rwl->lock);
274 			rwl->readers_waiting--;
275 			UNLOCK(&rwl->lock);
308 		rwl->write_granted = 0;
313 		prev_writer = isc_atomic_xadd(&rwl->write_requests, 1);
314 		while (rwl->write_completions != prev_writer) {
315 			LOCK(&rwl->lock);
316 			if (rwl->write_completions != prev_writer) {
317 				WAIT(&rwl->writeable, &rwl->lock);
318 				UNLOCK(&rwl->lock);
321 			UNLOCK(&rwl->lock);
326 			cntflag = isc_atomic_cmpxchg(&rwl->cnt_and_flag, 0,
332 			LOCK(&rwl->lock);
333 			if (rwl->cnt_and_flag != 0)
334 				WAIT(&rwl->writeable, &rwl->lock);
335 			UNLOCK(&rwl->lock);
338 		INSIST((rwl->cnt_and_flag & WRITER_ACTIVE) != 0);
339 		rwl->write_granted++;
344 				  ISC_MSG_POSTLOCK, "postlock"), rwl, type);
351 isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
354 	REQUIRE(VALID_RWLOCK(rwl));
358 				  ISC_MSG_PRELOCK, "prelock"), rwl, type);
363 		if (rwl->write_requests != rwl->write_completions)
367 		cntflag = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
373 			cntflag = isc_atomic_xadd(&rwl->cnt_and_flag,
380 			    rwl->write_completions != rwl->write_requests) {
381 				LOCK(&rwl->lock);
382 				BROADCAST(&rwl->writeable);
383 				UNLOCK(&rwl->lock);
390 		cntflag = isc_atomic_cmpxchg(&rwl->cnt_and_flag, 0,
399 		(void)isc_atomic_xadd(&rwl->write_completions, -1);
401 		rwl->write_granted++;
406 				  ISC_MSG_POSTLOCK, "postlock"), rwl, type);
413 isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
416 	REQUIRE(VALID_RWLOCK(rwl));
419 	prevcnt = isc_atomic_cmpxchg(&rwl->cnt_and_flag,
433 		(void)isc_atomic_xadd(&rwl->write_completions, -1);
442 isc_rwlock_downgrade(isc_rwlock_t *rwl) {
445 	REQUIRE(VALID_RWLOCK(rwl));
448 	prev_readers = isc_atomic_xadd(&rwl->cnt_and_flag, READER_INCR);
453 	(void)isc_atomic_xadd(&rwl->cnt_and_flag, -WRITER_ACTIVE);
454 	(void)isc_atomic_xadd(&rwl->write_completions, 1);
457 	LOCK(&rwl->lock);
458 	if (rwl->readers_waiting > 0)
459 		BROADCAST(&rwl->readable);
460 	UNLOCK(&rwl->lock);
464 isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
467 	REQUIRE(VALID_RWLOCK(rwl));
471 				  ISC_MSG_PREUNLOCK, "preunlock"), rwl, type);
475 		prev_cnt = isc_atomic_xadd(&rwl->cnt_and_flag, -READER_INCR);
483 		    rwl->write_completions != rwl->write_requests) {
484 			LOCK(&rwl->lock);
485 			BROADCAST(&rwl->writeable);
486 			UNLOCK(&rwl->lock);
495 		(void)isc_atomic_xadd(&rwl->cnt_and_flag, -WRITER_ACTIVE);
496 		(void)isc_atomic_xadd(&rwl->write_completions, 1);
498 		if (rwl->write_granted >= rwl->write_quota ||
499 		    rwl->write_requests == rwl->write_completions ||
500 		    (rwl->cnt_and_flag & ~WRITER_ACTIVE) != 0) {
509 			LOCK(&rwl->lock);
510 			if (rwl->readers_waiting > 0) {
512 				BROADCAST(&rwl->readable);
514 			UNLOCK(&rwl->lock);
517 		if (rwl->write_requests != rwl->write_completions &&
519 			LOCK(&rwl->lock);
520 			BROADCAST(&rwl->writeable);
521 			UNLOCK(&rwl->lock);
528 		   rwl, type);
537 doit(isc_rwlock_t *rwl, isc_rwlocktype_t type, isc_boolean_t nonblock) {
542 	REQUIRE(VALID_RWLOCK(rwl));
544 	LOCK(&rwl->lock);
548 				  ISC_MSG_PRELOCK, "prelock"), rwl, type);
552 		if (rwl->readers_waiting != 0)
556 			    ((rwl->active == 0 ||
557 			      (rwl->type == isc_rwlocktype_read &&
558 			       (rwl->writers_waiting == 0 ||
559 				rwl->granted < rwl->read_quota)))))
561 				rwl->type = isc_rwlocktype_read;
562 				rwl->active++;
563 				rwl->granted++;
570 				rwl->readers_waiting++;
571 				WAIT(&rwl->readable, &rwl->lock);
572 				rwl->readers_waiting--;
576 		if (rwl->writers_waiting != 0)
579 			if (!skip && rwl->active == 0) {
580 				rwl->type = isc_rwlocktype_write;
581 				rwl->active = 1;
582 				rwl->granted++;
589 				rwl->writers_waiting++;
590 				WAIT(&rwl->writeable, &rwl->lock);
591 				rwl->writers_waiting--;
598 				  ISC_MSG_POSTLOCK, "postlock"), rwl, type);
601 	UNLOCK(&rwl->lock);
607 isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
608 	return (doit(rwl, type, ISC_FALSE));
612 isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
613 	return (doit(rwl, type, ISC_TRUE));
617 isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
620 	REQUIRE(VALID_RWLOCK(rwl));
621 	LOCK(&rwl->lock);
622 	REQUIRE(rwl->type == isc_rwlocktype_read);
623 	REQUIRE(rwl->active != 0);
626 	if (rwl->active == 1) {
627 		rwl->original = (rwl->original == isc_rwlocktype_none) ?
629 		rwl->type = isc_rwlocktype_write;
633 	UNLOCK(&rwl->lock);
638 isc_rwlock_downgrade(isc_rwlock_t *rwl) {
640 	REQUIRE(VALID_RWLOCK(rwl));
641 	LOCK(&rwl->lock);
642 	REQUIRE(rwl->type == isc_rwlocktype_write);
643 	REQUIRE(rwl->active == 1);
645 	rwl->type = isc_rwlocktype_read;
646 	rwl->original = (rwl->original == isc_rwlocktype_none) ?
652 	if (rwl->original == isc_rwlocktype_none &&
653 	    (rwl->writers_waiting == 0 || rwl->granted < rwl->read_quota) &&
654 	    rwl->readers_waiting > 0)
655 		BROADCAST(&rwl->readable);
657 	UNLOCK(&rwl->lock);
661 isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
663 	REQUIRE(VALID_RWLOCK(rwl));
664 	LOCK(&rwl->lock);
665 	REQUIRE(rwl->type == type);
671 				  ISC_MSG_PREUNLOCK, "preunlock"), rwl, type);
674 	INSIST(rwl->active > 0);
675 	rwl->active--;
676 	if (rwl->active == 0) {
677 		if (rwl->original != isc_rwlocktype_none) {
678 			rwl->type = rwl->original;
679 			rwl->original = isc_rwlocktype_none;
681 		if (rwl->type == isc_rwlocktype_read) {
682 			rwl->granted = 0;
683 			if (rwl->writers_waiting > 0) {
684 				rwl->type = isc_rwlocktype_write;
685 				SIGNAL(&rwl->writeable);
686 			} else if (rwl->readers_waiting > 0) {
688 				BROADCAST(&rwl->readable);
691 			if (rwl->readers_waiting > 0) {
692 				if (rwl->writers_waiting > 0 &&
693 				    rwl->granted < rwl->write_quota) {
694 					SIGNAL(&rwl->writeable);
696 					rwl->granted = 0;
697 					rwl->type = isc_rwlocktype_read;
698 					BROADCAST(&rwl->readable);
700 			} else if (rwl->writers_waiting > 0) {
701 				rwl->granted = 0;
702 				SIGNAL(&rwl->writeable);
704 				rwl->granted = 0;
708 	INSIST(rwl->original == isc_rwlocktype_none);
713 		   rwl, type);
716 	UNLOCK(&rwl->lock);
725 isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
728 	REQUIRE(rwl != NULL);
733 	rwl->type = isc_rwlocktype_read;
734 	rwl->active = 0;
735 	rwl->magic = RWLOCK_MAGIC;
741 isc_rwlock_lock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
742 	REQUIRE(VALID_RWLOCK(rwl));
745 		if (rwl->type != isc_rwlocktype_read && rwl->active != 0)
747 		rwl->type = isc_rwlocktype_read;
748 		rwl->active++;
750 		if (rwl->active != 0)
752 		rwl->type = isc_rwlocktype_write;
753 		rwl->active = 1;
759 isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
760 	return (isc_rwlock_lock(rwl, type));
764 isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
767 	REQUIRE(VALID_RWLOCK(rwl));
768 	REQUIRE(rwl->type == isc_rwlocktype_read);
769 	REQUIRE(rwl->active != 0);
772 	if (rwl->active == 1)
773 		rwl->type = isc_rwlocktype_write;
780 isc_rwlock_downgrade(isc_rwlock_t *rwl) {
782 	REQUIRE(VALID_RWLOCK(rwl));
783 	REQUIRE(rwl->type == isc_rwlocktype_write);
784 	REQUIRE(rwl->active == 1);
786 	rwl->type = isc_rwlocktype_read;
790 isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
791 	REQUIRE(VALID_RWLOCK(rwl));
792 	REQUIRE(rwl->type == type);
796 	INSIST(rwl->active > 0);
797 	rwl->active--;
803 isc_rwlock_destroy(isc_rwlock_t *rwl) {
804 	REQUIRE(rwl != NULL);
805 	REQUIRE(rwl->active == 0);
806 	rwl->magic = 0;