lib/libthr/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  * $FreeBSD$
  27  */
  28
  29 #include <errno.h>
  30 #include <limits.h>
  31 #include <stdlib.h>
  32
  33 #include "namespace.h"
  34 #include <pthread.h>
  35 #include "un-namespace.h"
  36 #include "thr_private.h"
  37
  38 __weak_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
  39 __weak_reference(_pthread_rwlock_init, pthread_rwlock_init);
  40 __weak_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
  41 __weak_reference(_pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock);
  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 __weak_reference(_pthread_rwlock_timedwrlock, pthread_rwlock_timedwrlock);
  47
  48 /*
  49  * Prototypes
  50  */
  51
  52 static int
  53 rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr __unused)
  54 {
  55         pthread_rwlock_t prwlock;
  56
  57         prwlock = (pthread_rwlock_t)calloc(1, sizeof(struct pthread_rwlock));
  58         if (prwlock == NULL)
  59                 return (ENOMEM);
  60         *rwlock = prwlock;
  61         return (0);
  62 }
  63
  64 int
  65 _pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
  66 {
  67         int ret;
  68
  69         if (rwlock == NULL)
  70                 ret = EINVAL;
  71         else {
  72                 pthread_rwlock_t prwlock;
  73
  74                 prwlock = *rwlock;
  75                 *rwlock = NULL;
  76
  77                 free(prwlock);
  78                 ret = 0;
  79         }
  80         return (ret);
  81 }
  82
  83 static int
  84 init_static(struct pthread *thread, pthread_rwlock_t *rwlock)
  85 {
  86         int ret;
  87
  88         THR_LOCK_ACQUIRE(thread, &_rwlock_static_lock);
  89
  90         if (*rwlock == NULL)
  91                 ret = rwlock_init(rwlock, NULL);
  92         else
  93                 ret = 0;
  94
  95         THR_LOCK_RELEASE(thread, &_rwlock_static_lock);
  96
  97         return (ret);
  98 }
  99
 100 int
 101 _pthread_rwlock_init (pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
 102 {
 103         *rwlock = NULL;
 104         return (rwlock_init(rwlock, attr));
 105 }
 106
 107 static int
 108 rwlock_rdlock_common(pthread_rwlock_t *rwlock, const struct timespec *abstime)
 109 {
 110         struct pthread *curthread = _get_curthread();
 111         pthread_rwlock_t prwlock;
 112         struct timespec ts, ts2, *tsp;
 113         int flags;
 114         int ret;
 115
 116         if (__predict_false(rwlock == NULL))
 117                 return (EINVAL);
 118
 119         prwlock = *rwlock;
 120
 121         /* check for static initialization */
 122         if (__predict_false(prwlock == NULL)) {
 123                 if ((ret = init_static(curthread, rwlock)) != 0)
 124                         return (ret);
 125
 126                 prwlock = *rwlock;
 127         }
 128
 129         if (curthread->rdlock_count) {
 130                 /*
 131                  * To avoid having to track all the rdlocks held by
 132                  * a thread or all of the threads that hold a rdlock,
 133                  * we keep a simple count of all the rdlocks held by
 134                  * a thread.  If a thread holds any rdlocks it is
 135                  * possible that it is attempting to take a recursive
 136                  * rdlock.  If there are blocked writers and precedence
 137                  * is given to them, then that would result in the thread
 138                  * deadlocking.  So allowing a thread to take the rdlock
 139                  * when it already has one or more rdlocks avoids the
 140                  * deadlock.  I hope the reader can follow that logic ;-)
 141                  */
 142                 flags = URWLOCK_PREFER_READER;
 143         } else {
 144                 flags = 0;
 145         }
 146
 147         /*
 148          * POSIX said the validity of the abstimeout parameter need
 149          * not be checked if the lock can be immediately acquired.
 150          */
 151         ret = _thr_rwlock_tryrdlock(&prwlock->lock, flags);
 152         if (ret == 0) {
 153                 curthread->rdlock_count++;
 154                 return (ret);
 155         }
 156
 157         if (__predict_false(abstime &&
 158                 (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
 159                 return (EINVAL);
 160
 161         for (;;) {
 162                 if (abstime) {
 163                         clock_gettime(CLOCK_REALTIME, &ts);
 164                         TIMESPEC_SUB(&ts2, abstime, &ts);
 165                         if (ts2.tv_sec < 0 ||
 166                             (ts2.tv_sec == 0 && ts2.tv_nsec <= 0))
 167                                 return (ETIMEDOUT);
 168                         tsp = &ts2;
 169                 } else
 170                         tsp = NULL;
 171
 172                 /* goto kernel and lock it */
 173                 ret = __thr_rwlock_rdlock(&prwlock->lock, flags, tsp);
 174                 if (ret != EINTR)
 175                         break;
 176
 177                 /* if interrupted, try to lock it in userland again. */
 178                 if (_thr_rwlock_tryrdlock(&prwlock->lock, flags) == 0) {
 179                         ret = 0;
 180                         curthread->rdlock_count++;
 181                         break;
 182                 }
 183         }
 184         return (ret);
 185 }
 186
 187 int
 188 _pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
 189 {
 190         return (rwlock_rdlock_common(rwlock, NULL));
 191 }
 192
 193 int
 194 _pthread_rwlock_timedrdlock (pthread_rwlock_t *rwlock,
 195          const struct timespec *abstime)
 196 {
 197         return (rwlock_rdlock_common(rwlock, abstime));
 198 }
 199
 200 int
 201 _pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
 202 {
 203         struct pthread *curthread = _get_curthread();
 204         pthread_rwlock_t prwlock;
 205         int flags;
 206         int ret;
 207
 208         if (__predict_false(rwlock == NULL))
 209                 return (EINVAL);
 210
 211         prwlock = *rwlock;
 212
 213         /* check for static initialization */
 214         if (__predict_false(prwlock == NULL)) {
 215                 if ((ret = init_static(curthread, rwlock)) != 0)
 216                         return (ret);
 217
 218                 prwlock = *rwlock;
 219         }
 220
 221         if (curthread->rdlock_count) {
 222                 /*
 223                  * To avoid having to track all the rdlocks held by
 224                  * a thread or all of the threads that hold a rdlock,
 225                  * we keep a simple count of all the rdlocks held by
 226                  * a thread.  If a thread holds any rdlocks it is
 227                  * possible that it is attempting to take a recursive
 228                  * rdlock.  If there are blocked writers and precedence
 229                  * is given to them, then that would result in the thread
 230                  * deadlocking.  So allowing a thread to take the rdlock
 231                  * when it already has one or more rdlocks avoids the
 232                  * deadlock.  I hope the reader can follow that logic ;-)
 233                  */
 234                 flags = URWLOCK_PREFER_READER;
 235         } else {
 236                 flags = 0;
 237         }
 238
 239         ret = _thr_rwlock_tryrdlock(&prwlock->lock, flags);
 240         if (ret == 0)
 241                 curthread->rdlock_count++;
 242         return (ret);
 243 }
 244
 245 int
 246 _pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
 247 {
 248         struct pthread *curthread = _get_curthread();
 249         pthread_rwlock_t prwlock;
 250         int ret;
 251
 252         if (__predict_false(rwlock == NULL))
 253                 return (EINVAL);
 254
 255         prwlock = *rwlock;
 256
 257         /* check for static initialization */
 258         if (__predict_false(prwlock == NULL)) {
 259                 if ((ret = init_static(curthread, rwlock)) != 0)
 260                         return (ret);
 261
 262                 prwlock = *rwlock;
 263         }
 264
 265         ret = _thr_rwlock_trywrlock(&prwlock->lock);
 266         if (ret == 0)
 267                 prwlock->owner = curthread;
 268         return (ret);
 269 }
 270
 271 static int
 272 rwlock_wrlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
 273 {
 274         struct pthread *curthread = _get_curthread();
 275         pthread_rwlock_t prwlock;
 276         struct timespec ts, ts2, *tsp;
 277         int ret;
 278
 279         if (__predict_false(rwlock == NULL))
 280                 return (EINVAL);
 281
 282         prwlock = *rwlock;
 283
 284         /* check for static initialization */
 285         if (__predict_false(prwlock == NULL)) {
 286                 if ((ret = init_static(curthread, rwlock)) != 0)
 287                         return (ret);
 288
 289                 prwlock = *rwlock;
 290         }
 291
 292         /*
 293          * POSIX said the validity of the abstimeout parameter need
 294          * not be checked if the lock can be immediately acquired.
 295          */
 296         ret = _thr_rwlock_trywrlock(&prwlock->lock);
 297         if (ret == 0) {
 298                 prwlock->owner = curthread;
 299                 return (ret);
 300         }
 301
 302         if (__predict_false(abstime &&
 303                 (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
 304                 return (EINVAL);
 305
 306         for (;;) {
 307                 if (abstime != NULL) {
 308                         clock_gettime(CLOCK_REALTIME, &ts);
 309                         TIMESPEC_SUB(&ts2, abstime, &ts);
 310                         if (ts2.tv_sec < 0 ||
 311                             (ts2.tv_sec == 0 && ts2.tv_nsec <= 0))
 312                                 return (ETIMEDOUT);
 313                         tsp = &ts2;
 314                 } else
 315                         tsp = NULL;
 316
 317                 /* goto kernel and lock it */
 318                 ret = __thr_rwlock_wrlock(&prwlock->lock, tsp);
 319                 if (ret == 0) {
 320                         prwlock->owner = curthread;
 321                         break;
 322                 }
 323
 324                 if (ret != EINTR)
 325                         break;
 326
 327                 /* if interrupted, try to lock it in userland again. */
 328                 if (_thr_rwlock_trywrlock(&prwlock->lock) == 0) {
 329                         ret = 0;
 330                         prwlock->owner = curthread;
 331                         break;
 332                 }
 333         }
 334         return (ret);
 335 }
 336
 337 int
 338 _pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
 339 {
 340         return (rwlock_wrlock_common (rwlock, NULL));
 341 }
 342
 343 int
 344 _pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
 345     const struct timespec *abstime)
 346 {
 347         return (rwlock_wrlock_common (rwlock, abstime));
 348 }
 349
 350 int
 351 _pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
 352 {
 353         struct pthread *curthread = _get_curthread();
 354         pthread_rwlock_t prwlock;
 355         int ret;
 356         int32_t state;
 357
 358         if (__predict_false(rwlock == NULL))
 359                 return (EINVAL);
 360
 361         prwlock = *rwlock;
 362
 363         if (__predict_false(prwlock == NULL))
 364                 return (EINVAL);
 365
 366         state = prwlock->lock.rw_state;
 367         if (state & URWLOCK_WRITE_OWNER) {
 368                 if (__predict_false(prwlock->owner != curthread))
 369                         return (EPERM);
 370                 prwlock->owner = NULL;
 371         }
 372
 373         ret = _thr_rwlock_unlock(&prwlock->lock);
 374         if (ret == 0 && (state & URWLOCK_WRITE_OWNER) == 0)
 375                 curthread->rdlock_count--;
 376
 377         return (ret);
 378 }