1 /*-
2 * Copyright (c) 1998 Alex Nash
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 * $FreeBSD: src/lib/libpthread/thread/thr_rwlock.c,v 1.14 2004/01/08 15:37:09 deischen Exp $
27 */
28
29 #include "namespace.h"
30 #include <machine/tls.h>
31 #include <errno.h>
32 #include <limits.h>
33 #include <stdlib.h>
34 #include <pthread.h>
35 #include "un-namespace.h"
36 #include "thr_private.h"
37
38 #ifdef _PTHREADS_DEBUGGING
39
40 #include <stdio.h>
41 #include <stdarg.h>
42 #include <string.h>
43 #include <sys/file.h>
44
45 #endif
46
47 /* maximum number of times a read lock may be obtained */
48 #define MAX_READ_LOCKS (INT_MAX - 1)
49
50 umtx_t _rwlock_static_lock;
51
52 #ifdef _PTHREADS_DEBUGGING
53
54 static
55 void
rwlock_log(const char * ctl,...)56 rwlock_log(const char *ctl, ...)
57 {
58 char buf[256];
59 va_list va;
60 size_t len;
61
62 va_start(va, ctl);
63 len = vsnprintf(buf, sizeof(buf), ctl, va);
64 va_end(va);
65 _thr_log(buf, len);
66 }
67
68 #else
69
70 static __inline
71 void
rwlock_log(const char * ctl __unused,...)72 rwlock_log(const char *ctl __unused, ...)
73 {
74 }
75
76 #endif
77
78 static int
rwlock_init(pthread_rwlock_t * rwlock,const pthread_rwlockattr_t * attr __unused)79 rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr __unused)
80 {
81 pthread_rwlock_t prwlock;
82 int ret;
83
84 /* allocate rwlock object */
85 prwlock = __malloc(sizeof(struct __pthread_rwlock_s));
86 if (prwlock == NULL)
87 return (ENOMEM);
88
89 /* initialize the lock */
90 if ((ret = _pthread_mutex_init(&prwlock->lock, NULL)) != 0) {
91 __free(prwlock);
92 } else {
93 /* initialize the read condition signal */
94 ret = _pthread_cond_init(&prwlock->read_signal, NULL);
95
96 if (ret != 0) {
97 _pthread_mutex_destroy(&prwlock->lock);
98 __free(prwlock);
99 } else {
100 /* initialize the write condition signal */
101 ret = _pthread_cond_init(&prwlock->write_signal, NULL);
102
103 if (ret != 0) {
104 _pthread_cond_destroy(&prwlock->read_signal);
105 _pthread_mutex_destroy(&prwlock->lock);
106 __free(prwlock);
107 } else {
108 /* success */
109 prwlock->state = 0;
110 prwlock->blocked_writers = 0;
111 *rwlock = prwlock;
112 }
113 }
114 }
115
116 return (ret);
117 }
118
119 #if 0
120 void
121 _rwlock_reinit(pthread_rwlock_t prwlock)
122 {
123 _mutex_reinit(&prwlock->lock);
124 _cond_reinit(prwlock->read_signal);
125 prwlock->state = 0;
126 prwlock->blocked_writers = 0;
127 }
128 #endif
129
130 int
_pthread_rwlock_destroy(pthread_rwlock_t * rwlock)131 _pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
132 {
133 int ret;
134
135 if (rwlock == NULL) {
136 ret = EINVAL;
137 } else if (*rwlock == NULL) {
138 ret = 0;
139 } else {
140 pthread_rwlock_t prwlock;
141
142 prwlock = *rwlock;
143 rwlock_log("rwlock_destroy %p\n", prwlock);
144
145 _pthread_mutex_destroy(&prwlock->lock);
146 _pthread_cond_destroy(&prwlock->read_signal);
147 _pthread_cond_destroy(&prwlock->write_signal);
148 __free(prwlock);
149
150 *rwlock = NULL;
151
152 ret = 0;
153 }
154 return (ret);
155 }
156
157 static int
init_static(pthread_t thread,pthread_rwlock_t * rwlock)158 init_static(pthread_t thread, pthread_rwlock_t *rwlock)
159 {
160 int ret;
161
162 THR_LOCK_ACQUIRE(thread, &_rwlock_static_lock);
163
164 if (*rwlock == NULL)
165 ret = rwlock_init(rwlock, NULL);
166 else
167 ret = 0;
168
169 THR_LOCK_RELEASE(thread, &_rwlock_static_lock);
170
171 return (ret);
172 }
173
174 int
_pthread_rwlock_init(pthread_rwlock_t * rwlock,const pthread_rwlockattr_t * attr)175 _pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
176 {
177 *rwlock = NULL;
178 return (rwlock_init(rwlock, attr));
179 }
180
181 static int
rwlock_rdlock_common(pthread_rwlock_t * rwlock,const struct timespec * abstime)182 rwlock_rdlock_common(pthread_rwlock_t *rwlock, const struct timespec *abstime)
183 {
184 pthread_t curthread = tls_get_curthread();
185 pthread_rwlock_t prwlock;
186 int ret;
187
188 if (rwlock == NULL)
189 return (EINVAL);
190
191 prwlock = *rwlock;
192
193 /* check for static initialization */
194 if (prwlock == NULL) {
195 if ((ret = init_static(curthread, rwlock)) != 0)
196 return (ret);
197
198 prwlock = *rwlock;
199 }
200 rwlock_log("rwlock_rdlock_common %p\n", prwlock);
201
202 /* grab the monitor lock */
203 if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0) {
204 rwlock_log("rwlock_rdlock_common %p (failedA)\n", prwlock);
205 return (ret);
206 }
207
208 /* check lock count */
209 if (prwlock->state == MAX_READ_LOCKS) {
210 _pthread_mutex_unlock(&prwlock->lock);
211 rwlock_log("rwlock_rdlock_common %p (failedB)\n", prwlock);
212 return (EAGAIN);
213 }
214
215 curthread = tls_get_curthread();
216 if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
217 /*
218 * To avoid having to track all the rdlocks held by
219 * a thread or all of the threads that hold a rdlock,
220 * we keep a simple count of all the rdlocks held by
221 * a thread. If a thread holds any rdlocks it is
222 * possible that it is attempting to take a recursive
223 * rdlock. If there are blocked writers and precedence
224 * is given to them, then that would result in the thread
225 * deadlocking. So allowing a thread to take the rdlock
226 * when it already has one or more rdlocks avoids the
227 * deadlock. I hope the reader can follow that logic ;-)
228 */
229 ; /* nothing needed */
230 } else {
231 /*
232 * Give writers priority over readers
233 *
234 * WARNING: pthread_cond*() temporarily releases the
235 * mutex.
236 */
237 while (prwlock->blocked_writers || prwlock->state < 0) {
238 if (abstime) {
239 ret = _pthread_cond_timedwait(
240 &prwlock->read_signal,
241 &prwlock->lock, abstime);
242 } else {
243 ret = _pthread_cond_wait(
244 &prwlock->read_signal,
245 &prwlock->lock);
246 }
247 if (ret != 0) {
248 /* can't do a whole lot if this fails */
249 _pthread_mutex_unlock(&prwlock->lock);
250 rwlock_log("rwlock_rdlock_common %p "
251 "(failedC)\n", prwlock);
252 return (ret);
253 }
254 }
255 }
256
257 curthread->rdlock_count++;
258 prwlock->state++; /* indicate we are locked for reading */
259
260 /*
261 * Something is really wrong if this call fails. Returning
262 * error won't do because we've already obtained the read
263 * lock. Decrementing 'state' is no good because we probably
264 * don't have the monitor lock.
265 */
266 _pthread_mutex_unlock(&prwlock->lock);
267 rwlock_log("rwlock_rdlock_common %p (return %d)\n", prwlock, ret);
268
269 return (ret);
270 }
271
272 int
_pthread_rwlock_rdlock(pthread_rwlock_t * rwlock)273 _pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
274 {
275 return (rwlock_rdlock_common(rwlock, NULL));
276 }
277
278 int
_pthread_rwlock_timedrdlock(pthread_rwlock_t * __restrict rwlock,const struct timespec * __restrict abstime)279 _pthread_rwlock_timedrdlock (pthread_rwlock_t * __restrict rwlock,
280 const struct timespec * __restrict abstime)
281 {
282 return (rwlock_rdlock_common(rwlock, abstime));
283 }
284
285 int
_pthread_rwlock_tryrdlock(pthread_rwlock_t * rwlock)286 _pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
287 {
288 pthread_t curthread = tls_get_curthread();
289 pthread_rwlock_t prwlock;
290 int ret;
291
292 if (rwlock == NULL)
293 return (EINVAL);
294
295 prwlock = *rwlock;
296
297 /* check for static initialization */
298 if (prwlock == NULL) {
299 if ((ret = init_static(curthread, rwlock)) != 0)
300 return (ret);
301
302 prwlock = *rwlock;
303 }
304
305 /* grab the monitor lock */
306 if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
307 return (ret);
308
309 curthread = tls_get_curthread();
310 if (prwlock->state == MAX_READ_LOCKS)
311 ret = EAGAIN;
312 else if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
313 /* see comment for pthread_rwlock_rdlock() */
314 curthread->rdlock_count++;
315 prwlock->state++;
316 }
317 /* give writers priority over readers */
318 else if (prwlock->blocked_writers || prwlock->state < 0)
319 ret = EBUSY;
320 else {
321 curthread->rdlock_count++;
322 prwlock->state++; /* indicate we are locked for reading */
323 }
324
325 /* see the comment on this in pthread_rwlock_rdlock */
326 _pthread_mutex_unlock(&prwlock->lock);
327
328 return (ret);
329 }
330
331 int
_pthread_rwlock_trywrlock(pthread_rwlock_t * rwlock)332 _pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
333 {
334 pthread_t curthread = tls_get_curthread();
335 pthread_rwlock_t prwlock;
336 int ret;
337
338 if (rwlock == NULL)
339 return (EINVAL);
340
341 prwlock = *rwlock;
342
343 /* check for static initialization */
344 if (prwlock == NULL) {
345 if ((ret = init_static(curthread, rwlock)) != 0)
346 return (ret);
347
348 prwlock = *rwlock;
349 }
350
351 /* grab the monitor lock */
352 if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
353 return (ret);
354
355 if (prwlock->state != 0)
356 ret = EBUSY;
357 else
358 /* indicate we are locked for writing */
359 prwlock->state = -1;
360
361 /* see the comment on this in pthread_rwlock_rdlock */
362 _pthread_mutex_unlock(&prwlock->lock);
363
364 return (ret);
365 }
366
367 int
_pthread_rwlock_unlock(pthread_rwlock_t * rwlock)368 _pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
369 {
370 pthread_t curthread;
371 pthread_rwlock_t prwlock;
372 int ret;
373
374 if (rwlock == NULL)
375 return (EINVAL);
376
377 prwlock = *rwlock;
378
379 if (prwlock == NULL)
380 return (EINVAL);
381
382 rwlock_log("rwlock_unlock %p\n", prwlock);
383
384 /* grab the monitor lock */
385 if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
386 return (ret);
387
388 curthread = tls_get_curthread();
389 if (prwlock->state > 0) {
390 /*
391 * Unlock reader
392 */
393 curthread->rdlock_count--;
394 prwlock->state--;
395 if (prwlock->state == 0 && prwlock->blocked_writers)
396 ret = _pthread_cond_signal(&prwlock->write_signal);
397 } else if (prwlock->state < 0) {
398 /*
399 * unlock writer
400 */
401 prwlock->state = 0;
402
403 if (prwlock->blocked_writers)
404 ret = _pthread_cond_signal(&prwlock->write_signal);
405 else
406 ret = _pthread_cond_broadcast(&prwlock->read_signal);
407 } else {
408 ret = EINVAL;
409 }
410
411 /* see the comment on this in pthread_rwlock_rdlock */
412 _pthread_mutex_unlock(&prwlock->lock);
413 rwlock_log("rwlock_unlock %p (return %d)\n", prwlock, ret);
414
415 return (ret);
416 }
417
418 static int
rwlock_wrlock_common(pthread_rwlock_t * rwlock,const struct timespec * abstime)419 rwlock_wrlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
420 {
421 pthread_t curthread = tls_get_curthread();
422 pthread_rwlock_t prwlock;
423 int ret;
424
425 if (rwlock == NULL)
426 return (EINVAL);
427
428 prwlock = *rwlock;
429
430 /* check for static initialization */
431 if (prwlock == NULL) {
432 if ((ret = init_static(curthread, rwlock)) != 0)
433 return (ret);
434
435 prwlock = *rwlock;
436 }
437 rwlock_log("rwlock_wrlock_common %p\n", prwlock);
438
439 /* grab the monitor lock */
440 if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0) {
441 rwlock_log("rwlock_wrlock_common %p (failedA)\n", prwlock);
442 return (ret);
443 }
444
445 while (prwlock->state != 0) {
446 prwlock->blocked_writers++;
447
448 /*
449 * WARNING: pthread_cond*() temporarily releases the
450 * mutex.
451 */
452 if (abstime != NULL) {
453 ret = _pthread_cond_timedwait(&prwlock->write_signal,
454 &prwlock->lock,
455 abstime);
456 } else {
457 ret = _pthread_cond_wait(&prwlock->write_signal,
458 &prwlock->lock);
459 }
460
461 /*
462 * Undo on failure. When the blocked_writers count drops
463 * to 0 we may have to wakeup blocked readers.
464 */
465 if (ret != 0) {
466 prwlock->blocked_writers--;
467 if (prwlock->blocked_writers == 0 &&
468 prwlock->state >= 0) {
469 _pthread_cond_broadcast(&prwlock->read_signal);
470 }
471 _pthread_mutex_unlock(&prwlock->lock);
472 rwlock_log("rwlock_wrlock_common %p (failedB %d)\n",
473 prwlock, ret);
474 return (ret);
475 }
476
477 prwlock->blocked_writers--;
478 }
479
480 /* indicate we are locked for writing */
481 prwlock->state = -1;
482
483 /* see the comment on this in pthread_rwlock_rdlock */
484 _pthread_mutex_unlock(&prwlock->lock);
485 rwlock_log("rwlock_wrlock_common %p (returns %d)\n", prwlock, ret);
486
487 return (ret);
488 }
489
490 int
_pthread_rwlock_wrlock(pthread_rwlock_t * rwlock)491 _pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
492 {
493 return (rwlock_wrlock_common (rwlock, NULL));
494 }
495
496 int
_pthread_rwlock_timedwrlock(pthread_rwlock_t * __restrict rwlock,const struct timespec * __restrict abstime)497 _pthread_rwlock_timedwrlock (pthread_rwlock_t * __restrict rwlock,
498 const struct timespec * __restrict abstime)
499 {
500 return (rwlock_wrlock_common (rwlock, abstime));
501 }
502
503 __strong_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
504 __strong_reference(_pthread_rwlock_init, pthread_rwlock_init);
505 __strong_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
506 __strong_reference(_pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock);
507 __strong_reference(_pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock);
508 __strong_reference(_pthread_rwlock_trywrlock, pthread_rwlock_trywrlock);
509 __strong_reference(_pthread_rwlock_unlock, pthread_rwlock_unlock);
510 __strong_reference(_pthread_rwlock_wrlock, pthread_rwlock_wrlock);
511 __strong_reference(_pthread_rwlock_timedwrlock, pthread_rwlock_timedwrlock);
512