lib/libc_r/uthread/uthread_rwlock.c

   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/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 1.3 2005/05/30 20:50:53 joerg Exp $
  28  */
  29
  30 #include <errno.h>
  31 #include <limits.h>
  32 #include <stdlib.h>
  33
  34 #include <pthread.h>
  35 #include "pthread_private.h"
  36
  37 /* maximum number of times a read lock may be obtained */
  38 #define MAX_READ_LOCKS          (INT_MAX - 1)
  39
  40 static int init_static (pthread_rwlock_t *rwlock);
  41
  42 static spinlock_t static_init_lock = _SPINLOCK_INITIALIZER;
  43
  44 static int
  45 init_static (pthread_rwlock_t *rwlock)
  46 {
  47         int ret;
  48
  49         _SPINLOCK(&static_init_lock);
  50
  51         if (*rwlock == NULL)
  52                 ret = pthread_rwlock_init(rwlock, NULL);
  53         else
  54                 ret = 0;
  55
  56         _SPINUNLOCK(&static_init_lock);
  57
  58         return(ret);
  59 }
  60
  61 int
  62 _pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
  63 {
  64         int ret;
  65
  66         if (rwlock == NULL)
  67                 ret = EINVAL;
  68         else {
  69                 pthread_rwlock_t prwlock;
  70
  71                 prwlock = *rwlock;
  72
  73                 pthread_mutex_destroy(&prwlock->lock);
  74                 pthread_cond_destroy(&prwlock->read_signal);
  75                 pthread_cond_destroy(&prwlock->write_signal);
  76                 free(prwlock);
  77
  78                 *rwlock = NULL;
  79
  80                 ret = 0;
  81         }
  82
  83         return(ret);
  84 }
  85
  86 int
  87 _pthread_rwlock_init (pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
  88 {
  89         pthread_rwlock_t        prwlock;
  90         int                     ret;
  91
  92         /* allocate rwlock object */
  93         prwlock = (pthread_rwlock_t)malloc(sizeof(struct pthread_rwlock));
  94
  95         if (prwlock == NULL)
  96                 return(ENOMEM);
  97
  98         /* initialize the lock */
  99         if ((ret = pthread_mutex_init(&prwlock->lock, NULL)) != 0)
 100                 free(prwlock);
 101         else {
 102                 /* initialize the read condition signal */
 103                 ret = pthread_cond_init(&prwlock->read_signal, NULL);
 104
 105                 if (ret != 0) {
 106                         pthread_mutex_destroy(&prwlock->lock);
 107                         free(prwlock);
 108                 } else {
 109                         /* initialize the write condition signal */
 110                         ret = pthread_cond_init(&prwlock->write_signal, NULL);
 111
 112                         if (ret != 0) {
 113                                 pthread_cond_destroy(&prwlock->read_signal);
 114                                 pthread_mutex_destroy(&prwlock->lock);
 115                                 free(prwlock);
 116                         } else {
 117                                 /* success */
 118                                 prwlock->state           = 0;
 119                                 prwlock->blocked_writers = 0;
 120
 121                                 *rwlock = prwlock;
 122                         }
 123                 }
 124         }
 125
 126         return(ret);
 127 }
 128
 129 int
 130 _pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
 131 {
 132         pthread_rwlock_t        prwlock;
 133         int                     ret;
 134
 135         if (rwlock == NULL)
 136                 return(EINVAL);
 137
 138         prwlock = *rwlock;
 139
 140         /* check for static initialization */
 141         if (prwlock == NULL) {
 142                 if ((ret = init_static(rwlock)) != 0)
 143                         return(ret);
 144
 145                 prwlock = *rwlock;
 146         }
 147
 148         /* grab the monitor lock */
 149         if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
 150                 return(ret);
 151
 152         /* give writers priority over readers */
 153         while (prwlock->blocked_writers || prwlock->state < 0) {
 154                 ret = pthread_cond_wait(&prwlock->read_signal, &prwlock->lock);
 155
 156                 if (ret != 0) {
 157                         /* can't do a whole lot if this fails */
 158                         pthread_mutex_unlock(&prwlock->lock);
 159                         return(ret);
 160                 }
 161         }
 162
 163         /* check lock count */
 164         if (prwlock->state == MAX_READ_LOCKS)
 165                 ret = EAGAIN;
 166         else
 167                 ++prwlock->state; /* indicate we are locked for reading */
 168
 169         /*
 170          * Something is really wrong if this call fails.  Returning
 171          * error won't do because we've already obtained the read
 172          * lock.  Decrementing 'state' is no good because we probably
 173          * don't have the monitor lock.
 174          */
 175         pthread_mutex_unlock(&prwlock->lock);
 176
 177         return(ret);
 178 }
 179
 180 int
 181 _pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
 182 {
 183         pthread_rwlock_t        prwlock;
 184         int                     ret;
 185
 186         if (rwlock == NULL)
 187                 return(EINVAL);
 188
 189         prwlock = *rwlock;
 190
 191         /* check for static initialization */
 192         if (prwlock == NULL) {
 193                 if ((ret = init_static(rwlock)) != 0)
 194                         return(ret);
 195
 196                 prwlock = *rwlock;
 197         }
 198
 199         /* grab the monitor lock */
 200         if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
 201                 return(ret);
 202
 203         /* give writers priority over readers */
 204         if (prwlock->blocked_writers || prwlock->state < 0)
 205                 ret = EBUSY;
 206         else if (prwlock->state == MAX_READ_LOCKS)
 207                 ret = EAGAIN; /* too many read locks acquired */
 208         else
 209                 ++prwlock->state; /* indicate we are locked for reading */
 210
 211         /* see the comment on this in pthread_rwlock_rdlock */
 212         pthread_mutex_unlock(&prwlock->lock);
 213
 214         return(ret);
 215 }
 216
 217 int
 218 _pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
 219 {
 220         pthread_rwlock_t        prwlock;
 221         int                     ret;
 222
 223         if (rwlock == NULL)
 224                 return(EINVAL);
 225
 226         prwlock = *rwlock;
 227
 228         /* check for static initialization */
 229         if (prwlock == NULL) {
 230                 if ((ret = init_static(rwlock)) != 0)
 231                         return(ret);
 232
 233                 prwlock = *rwlock;
 234         }
 235
 236         /* grab the monitor lock */
 237         if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
 238                 return(ret);
 239
 240         if (prwlock->state != 0)
 241                 ret = EBUSY;
 242         else
 243                 /* indicate we are locked for writing */
 244                 prwlock->state = -1;
 245
 246         /* see the comment on this in pthread_rwlock_rdlock */
 247         pthread_mutex_unlock(&prwlock->lock);
 248
 249         return(ret);
 250 }
 251
 252 int
 253 _pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
 254 {
 255         pthread_rwlock_t        prwlock;
 256         int                     ret;
 257
 258         if (rwlock == NULL)
 259                 return(EINVAL);
 260
 261         prwlock = *rwlock;
 262
 263         if (prwlock == NULL)
 264                 return(EINVAL);
 265
 266         /* grab the monitor lock */
 267         if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
 268                 return(ret);
 269
 270         if (prwlock->state > 0) {
 271                 if (--prwlock->state == 0 && prwlock->blocked_writers)
 272                         ret = pthread_cond_signal(&prwlock->write_signal);
 273         } else if (prwlock->state < 0) {
 274                 prwlock->state = 0;
 275
 276                 if (prwlock->blocked_writers)
 277                         ret = pthread_cond_signal(&prwlock->write_signal);
 278                 else
 279                         ret = pthread_cond_broadcast(&prwlock->read_signal);
 280         } else
 281                 ret = EINVAL;
 282
 283         /* see the comment on this in pthread_rwlock_rdlock */
 284         pthread_mutex_unlock(&prwlock->lock);
 285
 286         return(ret);
 287 }
 288
 289 int
 290 _pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
 291 {
 292         pthread_rwlock_t        prwlock;
 293         int                     ret;
 294
 295         if (rwlock == NULL)
 296                 return(EINVAL);
 297
 298         prwlock = *rwlock;
 299
 300         /* check for static initialization */
 301         if (prwlock == NULL) {
 302                 if ((ret = init_static(rwlock)) != 0)
 303                         return(ret);
 304
 305                 prwlock = *rwlock;
 306         }
 307
 308         /* grab the monitor lock */
 309         if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
 310                 return(ret);
 311
 312         while (prwlock->state != 0) {
 313                 ++prwlock->blocked_writers;
 314
 315                 ret = pthread_cond_wait(&prwlock->write_signal, &prwlock->lock);
 316
 317                 if (ret != 0) {
 318                         --prwlock->blocked_writers;
 319                         pthread_mutex_unlock(&prwlock->lock);
 320                         return(ret);
 321                 }
 322
 323                 --prwlock->blocked_writers;
 324         }
 325
 326         /* indicate we are locked for writing */
 327         prwlock->state = -1;
 328
 329         /* see the comment on this in pthread_rwlock_rdlock */
 330         pthread_mutex_unlock(&prwlock->lock);
 331
 332         return(ret);
 333 }
 334
 335 __strong_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
 336 __strong_reference(_pthread_rwlock_init, pthread_rwlock_init);
 337 __strong_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
 338 __strong_reference(_pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock);
 339 __strong_reference(_pthread_rwlock_trywrlock, pthread_rwlock_trywrlock);
 340 __strong_reference(_pthread_rwlock_unlock, pthread_rwlock_unlock);
 341 __strong_reference(_pthread_rwlock_wrlock, pthread_rwlock_wrlock);