2 * Copyright (c) 1998 Alex Nash
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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.
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
26 * $FreeBSD: src/lib/libc_r/uthread/uthread_rwlock.c,v 1.4.2.2 2002/10/22 14:44:03 fjoe Exp $
27 * $DragonFly: src/lib/libc_r/uthread/uthread_rwlock.c,v 1.2 2003/06/17 04:26:48 dillon Exp $
35 #include "pthread_private.h"
37 /* maximum number of times a read lock may be obtained */
38 #define MAX_READ_LOCKS (INT_MAX - 1)
40 __weak_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
41 __weak_reference(_pthread_rwlock_init, pthread_rwlock_init);
42 __weak_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
43 __weak_reference(_pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock);
44 __weak_reference(_pthread_rwlock_trywrlock, pthread_rwlock_trywrlock);
45 __weak_reference(_pthread_rwlock_unlock, pthread_rwlock_unlock);
46 __weak_reference(_pthread_rwlock_wrlock, pthread_rwlock_wrlock);
48 static int init_static (pthread_rwlock_t *rwlock);
50 static spinlock_t static_init_lock = _SPINLOCK_INITIALIZER;
53 init_static (pthread_rwlock_t *rwlock)
57 _SPINLOCK(&static_init_lock);
60 ret = pthread_rwlock_init(rwlock, NULL);
64 _SPINUNLOCK(&static_init_lock);
70 _pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
77 pthread_rwlock_t prwlock;
81 pthread_mutex_destroy(&prwlock->lock);
82 pthread_cond_destroy(&prwlock->read_signal);
83 pthread_cond_destroy(&prwlock->write_signal);
95 _pthread_rwlock_init (pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
97 pthread_rwlock_t prwlock;
100 /* allocate rwlock object */
101 prwlock = (pthread_rwlock_t)malloc(sizeof(struct pthread_rwlock));
106 /* initialize the lock */
107 if ((ret = pthread_mutex_init(&prwlock->lock, NULL)) != 0)
110 /* initialize the read condition signal */
111 ret = pthread_cond_init(&prwlock->read_signal, NULL);
114 pthread_mutex_destroy(&prwlock->lock);
117 /* initialize the write condition signal */
118 ret = pthread_cond_init(&prwlock->write_signal, NULL);
121 pthread_cond_destroy(&prwlock->read_signal);
122 pthread_mutex_destroy(&prwlock->lock);
127 prwlock->blocked_writers = 0;
138 _pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
140 pthread_rwlock_t prwlock;
148 /* check for static initialization */
149 if (prwlock == NULL) {
150 if ((ret = init_static(rwlock)) != 0)
156 /* grab the monitor lock */
157 if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
160 /* give writers priority over readers */
161 while (prwlock->blocked_writers || prwlock->state < 0) {
162 ret = pthread_cond_wait(&prwlock->read_signal, &prwlock->lock);
165 /* can't do a whole lot if this fails */
166 pthread_mutex_unlock(&prwlock->lock);
171 /* check lock count */
172 if (prwlock->state == MAX_READ_LOCKS)
175 ++prwlock->state; /* indicate we are locked for reading */
178 * Something is really wrong if this call fails. Returning
179 * error won't do because we've already obtained the read
180 * lock. Decrementing 'state' is no good because we probably
181 * don't have the monitor lock.
183 pthread_mutex_unlock(&prwlock->lock);
189 _pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
191 pthread_rwlock_t prwlock;
199 /* check for static initialization */
200 if (prwlock == NULL) {
201 if ((ret = init_static(rwlock)) != 0)
207 /* grab the monitor lock */
208 if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
211 /* give writers priority over readers */
212 if (prwlock->blocked_writers || prwlock->state < 0)
214 else if (prwlock->state == MAX_READ_LOCKS)
215 ret = EAGAIN; /* too many read locks acquired */
217 ++prwlock->state; /* indicate we are locked for reading */
219 /* see the comment on this in pthread_rwlock_rdlock */
220 pthread_mutex_unlock(&prwlock->lock);
226 _pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
228 pthread_rwlock_t prwlock;
236 /* check for static initialization */
237 if (prwlock == NULL) {
238 if ((ret = init_static(rwlock)) != 0)
244 /* grab the monitor lock */
245 if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
248 if (prwlock->state != 0)
251 /* indicate we are locked for writing */
254 /* see the comment on this in pthread_rwlock_rdlock */
255 pthread_mutex_unlock(&prwlock->lock);
261 _pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
263 pthread_rwlock_t prwlock;
274 /* grab the monitor lock */
275 if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
278 if (prwlock->state > 0) {
279 if (--prwlock->state == 0 && prwlock->blocked_writers)
280 ret = pthread_cond_signal(&prwlock->write_signal);
281 } else if (prwlock->state < 0) {
284 if (prwlock->blocked_writers)
285 ret = pthread_cond_signal(&prwlock->write_signal);
287 ret = pthread_cond_broadcast(&prwlock->read_signal);
291 /* see the comment on this in pthread_rwlock_rdlock */
292 pthread_mutex_unlock(&prwlock->lock);
298 _pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
300 pthread_rwlock_t prwlock;
308 /* check for static initialization */
309 if (prwlock == NULL) {
310 if ((ret = init_static(rwlock)) != 0)
316 /* grab the monitor lock */
317 if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
320 while (prwlock->state != 0) {
321 ++prwlock->blocked_writers;
323 ret = pthread_cond_wait(&prwlock->write_signal, &prwlock->lock);
326 --prwlock->blocked_writers;
327 pthread_mutex_unlock(&prwlock->lock);
331 --prwlock->blocked_writers;
334 /* indicate we are locked for writing */
337 /* see the comment on this in pthread_rwlock_rdlock */
338 pthread_mutex_unlock(&prwlock->lock);