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