lib/libthread_xu/thread/thr_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/libpthread/thread/thr_rwlock.c,v 1.14 2004/01/08 15:37:09 deischen Exp $
  27  * $DragonFly: src/lib/libthread_xu/thread/thr_rwlock.c,v 1.4 2005/04/12 14:01:31 davidxu Exp $
  28  */
  29
  30 #include <machine/tls.h>
  31
  32 #include <errno.h>
  33 #include <limits.h>
  34 #include <stdlib.h>
  35
  36 #include <pthread.h>
  37 #include "thr_private.h"
  38
  39 /* maximum number of times a read lock may be obtained */
  40 #define MAX_READ_LOCKS          (INT_MAX - 1)
  41
  42 __weak_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
  43 __weak_reference(_pthread_rwlock_init, pthread_rwlock_init);
  44 __weak_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
  45 __weak_reference(_pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock);
  46 __weak_reference(_pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock);
  47 __weak_reference(_pthread_rwlock_trywrlock, pthread_rwlock_trywrlock);
  48 __weak_reference(_pthread_rwlock_unlock, pthread_rwlock_unlock);
  49 __weak_reference(_pthread_rwlock_wrlock, pthread_rwlock_wrlock);
  50 __weak_reference(_pthread_rwlock_timedwrlock, pthread_rwlock_timedwrlock);
  51
  52 /*
  53  * Prototypes
  54  */
  55
  56 static int
  57 rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
  58 {
  59         pthread_rwlock_t prwlock;
  60         int ret;
  61
  62         /* allocate rwlock object */
  63         prwlock = (pthread_rwlock_t)malloc(sizeof(struct pthread_rwlock));
  64
  65         if (prwlock == NULL)
  66                 return (ENOMEM);
  67
  68         /* initialize the lock */
  69         if ((ret = _pthread_mutex_init(&prwlock->lock, NULL)) != 0)
  70                 free(prwlock);
  71         else {
  72                 /* initialize the read condition signal */
  73                 ret = _pthread_cond_init(&prwlock->read_signal, NULL);
  74
  75                 if (ret != 0) {
  76                         _pthread_mutex_destroy(&prwlock->lock);
  77                         free(prwlock);
  78                 } else {
  79                         /* initialize the write condition signal */
  80                         ret = _pthread_cond_init(&prwlock->write_signal, NULL);
  81
  82                         if (ret != 0) {
  83                                 _pthread_cond_destroy(&prwlock->read_signal);
  84                                 _pthread_mutex_destroy(&prwlock->lock);
  85                                 free(prwlock);
  86                         } else {
  87                                 /* success */
  88                                 prwlock->state = 0;
  89                                 prwlock->blocked_writers = 0;
  90                                 *rwlock = prwlock;
  91                         }
  92                 }
  93         }
  94
  95         return (ret);
  96 }
  97
  98 int
  99 _pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
 100 {
 101         int ret;
 102
 103         if (rwlock == NULL)
 104                 ret = EINVAL;
 105         else {
 106                 pthread_rwlock_t prwlock;
 107
 108                 prwlock = *rwlock;
 109
 110                 _pthread_mutex_destroy(&prwlock->lock);
 111                 _pthread_cond_destroy(&prwlock->read_signal);
 112                 _pthread_cond_destroy(&prwlock->write_signal);
 113                 free(prwlock);
 114
 115                 *rwlock = NULL;
 116
 117                 ret = 0;
 118         }
 119         return (ret);
 120 }
 121
 122 static int
 123 init_static(struct pthread *thread, pthread_rwlock_t *rwlock)
 124 {
 125         int ret;
 126
 127         THR_LOCK_ACQUIRE(thread, &_rwlock_static_lock);
 128
 129         if (*rwlock == NULL)
 130                 ret = rwlock_init(rwlock, NULL);
 131         else
 132                 ret = 0;
 133
 134         THR_LOCK_RELEASE(thread, &_rwlock_static_lock);
 135
 136         return (ret);
 137 }
 138
 139 int
 140 _pthread_rwlock_init (pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
 141 {
 142         *rwlock = NULL;
 143         return (rwlock_init(rwlock, attr));
 144 }
 145
 146 static int
 147 rwlock_rdlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
 148 {
 149         struct pthread *curthread = tls_get_curthread();
 150         pthread_rwlock_t prwlock;
 151         int ret;
 152
 153         if (rwlock == NULL)
 154                 return (EINVAL);
 155
 156         prwlock = *rwlock;
 157
 158         /* check for static initialization */
 159         if (prwlock == NULL) {
 160                 if ((ret = init_static(curthread, rwlock)) != 0)
 161                         return (ret);
 162
 163                 prwlock = *rwlock;
 164         }
 165
 166         /* grab the monitor lock */
 167         if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
 168                 return (ret);
 169
 170         /* check lock count */
 171         if (prwlock->state == MAX_READ_LOCKS) {
 172                 _pthread_mutex_unlock(&prwlock->lock);
 173                 return (EAGAIN);
 174         }
 175
 176         curthread = tls_get_curthread();
 177         if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
 178                 /*
 179                  * To avoid having to track all the rdlocks held by
 180                  * a thread or all of the threads that hold a rdlock,
 181                  * we keep a simple count of all the rdlocks held by
 182                  * a thread.  If a thread holds any rdlocks it is
 183                  * possible that it is attempting to take a recursive
 184                  * rdlock.  If there are blocked writers and precedence
 185                  * is given to them, then that would result in the thread
 186                  * deadlocking.  So allowing a thread to take the rdlock
 187                  * when it already has one or more rdlocks avoids the
 188                  * deadlock.  I hope the reader can follow that logic ;-)
 189                  */
 190                 ;       /* nothing needed */
 191         } else {
 192                 /* give writers priority over readers */
 193                 while (prwlock->blocked_writers || prwlock->state < 0) {
 194                         if (abstime)
 195                                 ret = _pthread_cond_timedwait
 196                                     (&prwlock->read_signal,
 197                                     &prwlock->lock, abstime);
 198                         else
 199                                 ret = _pthread_cond_wait(&prwlock->read_signal,
 200                             &prwlock->lock);
 201                         if (ret != 0) {
 202                                 /* can't do a whole lot if this fails */
 203                                 _pthread_mutex_unlock(&prwlock->lock);
 204                                 return (ret);
 205                         }
 206                 }
 207         }
 208
 209         curthread->rdlock_count++;
 210         prwlock->state++; /* indicate we are locked for reading */
 211
 212         /*
 213          * Something is really wrong if this call fails.  Returning
 214          * error won't do because we've already obtained the read
 215          * lock.  Decrementing 'state' is no good because we probably
 216          * don't have the monitor lock.
 217          */
 218         _pthread_mutex_unlock(&prwlock->lock);
 219
 220         return (ret);
 221 }
 222
 223 int
 224 _pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
 225 {
 226         return (rwlock_rdlock_common(rwlock, NULL));
 227 }
 228
 229 int
 230 _pthread_rwlock_timedrdlock (pthread_rwlock_t *rwlock,
 231          const struct timespec *abstime)
 232 {
 233         return (rwlock_rdlock_common(rwlock, abstime));
 234 }
 235
 236 int
 237 _pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
 238 {
 239         struct pthread *curthread = tls_get_curthread();
 240         pthread_rwlock_t prwlock;
 241         int ret;
 242
 243         if (rwlock == NULL)
 244                 return (EINVAL);
 245
 246         prwlock = *rwlock;
 247
 248         /* check for static initialization */
 249         if (prwlock == NULL) {
 250                 if ((ret = init_static(curthread, rwlock)) != 0)
 251                         return (ret);
 252
 253                 prwlock = *rwlock;
 254         }
 255
 256         /* grab the monitor lock */
 257         if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
 258                 return (ret);
 259
 260         curthread = tls_get_curthread();
 261         if (prwlock->state == MAX_READ_LOCKS)
 262                 ret = EAGAIN;
 263         else if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
 264                 /* see comment for pthread_rwlock_rdlock() */
 265                 curthread->rdlock_count++;
 266                 prwlock->state++;
 267         }
 268         /* give writers priority over readers */
 269         else if (prwlock->blocked_writers || prwlock->state < 0)
 270                 ret = EBUSY;
 271         else {
 272                 curthread->rdlock_count++;
 273                 prwlock->state++; /* indicate we are locked for reading */
 274         }
 275
 276         /* see the comment on this in pthread_rwlock_rdlock */
 277         _pthread_mutex_unlock(&prwlock->lock);
 278
 279         return (ret);
 280 }
 281
 282 int
 283 _pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
 284 {
 285         struct pthread *curthread = tls_get_curthread();
 286         pthread_rwlock_t prwlock;
 287         int ret;
 288
 289         if (rwlock == NULL)
 290                 return (EINVAL);
 291
 292         prwlock = *rwlock;
 293
 294         /* check for static initialization */
 295         if (prwlock == NULL) {
 296                 if ((ret = init_static(curthread, rwlock)) != 0)
 297                         return (ret);
 298
 299                 prwlock = *rwlock;
 300         }
 301
 302         /* grab the monitor lock */
 303         if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
 304                 return (ret);
 305
 306         if (prwlock->state != 0)
 307                 ret = EBUSY;
 308         else
 309                 /* indicate we are locked for writing */
 310                 prwlock->state = -1;
 311
 312         /* see the comment on this in pthread_rwlock_rdlock */
 313         _pthread_mutex_unlock(&prwlock->lock);
 314
 315         return (ret);
 316 }
 317
 318 int
 319 _pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
 320 {
 321         struct pthread *curthread;
 322         pthread_rwlock_t prwlock;
 323         int ret;
 324
 325         if (rwlock == NULL)
 326                 return (EINVAL);
 327
 328         prwlock = *rwlock;
 329
 330         if (prwlock == NULL)
 331                 return (EINVAL);
 332
 333         /* grab the monitor lock */
 334         if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
 335                 return (ret);
 336
 337         curthread = tls_get_curthread();
 338         if (prwlock->state > 0) {
 339                 curthread->rdlock_count--;
 340                 prwlock->state--;
 341                 if (prwlock->state == 0 && prwlock->blocked_writers)
 342                         ret = _pthread_cond_signal(&prwlock->write_signal);
 343         } else if (prwlock->state < 0) {
 344                 prwlock->state = 0;
 345
 346                 if (prwlock->blocked_writers)
 347                         ret = _pthread_cond_signal(&prwlock->write_signal);
 348                 else
 349                         ret = _pthread_cond_broadcast(&prwlock->read_signal);
 350         } else
 351                 ret = EINVAL;
 352
 353         /* see the comment on this in pthread_rwlock_rdlock */
 354         _pthread_mutex_unlock(&prwlock->lock);
 355
 356         return (ret);
 357 }
 358
 359 static int
 360 rwlock_wrlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
 361 {
 362         struct pthread *curthread = tls_get_curthread();
 363         pthread_rwlock_t prwlock;
 364         int ret;
 365
 366         if (rwlock == NULL)
 367                 return (EINVAL);
 368
 369         prwlock = *rwlock;
 370
 371         /* check for static initialization */
 372         if (prwlock == NULL) {
 373                 if ((ret = init_static(curthread, rwlock)) != 0)
 374                         return (ret);
 375
 376                 prwlock = *rwlock;
 377         }
 378
 379         /* grab the monitor lock */
 380         if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
 381                 return (ret);
 382
 383         while (prwlock->state != 0) {
 384                 prwlock->blocked_writers++;
 385
 386                 if (abstime != NULL)
 387                         ret = _pthread_cond_timedwait(&prwlock->write_signal,
 388                             &prwlock->lock, abstime);
 389                 else
 390                         ret = _pthread_cond_wait(&prwlock->write_signal,
 391                             &prwlock->lock);
 392                 if (ret != 0) {
 393                         prwlock->blocked_writers--;
 394                         _pthread_mutex_unlock(&prwlock->lock);
 395                         return (ret);
 396                 }
 397
 398                 prwlock->blocked_writers--;
 399         }
 400
 401         /* indicate we are locked for writing */
 402         prwlock->state = -1;
 403
 404         /* see the comment on this in pthread_rwlock_rdlock */
 405         _pthread_mutex_unlock(&prwlock->lock);
 406
 407         return (ret);
 408 }
 409
 410 int
 411 _pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
 412 {
 413         return (rwlock_wrlock_common (rwlock, NULL));
 414 }
 415
 416 int
 417 _pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
 418     const struct timespec *abstime)
 419 {
 420         return (rwlock_wrlock_common (rwlock, abstime));
 421 }