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