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 (*rwlock == THR_PSHARED_PTR) {                                       \
  50                 prwlock = __thr_pshared_offpage(rwlock, 0);                     \
  51                 if (prwlock == NULL)                                            \
  52                         return (EINVAL);                                        \
  53         } else if (__predict_false((prwlock = (*rwlock)) <=                     \
  54             THR_RWLOCK_DESTROYED)) {                                            \
  55                 if (prwlock == THR_RWLOCK_INITIALIZER) {                        \
  56                         int ret;                                                \
  57                         ret = init_static(_get_curthread(), rwlock);            \
  58                         if (ret)                                                \
  59                                 return (ret);                                   \
  60                 } else if (prwlock == THR_RWLOCK_DESTROYED) {                   \
  61                         return (EINVAL);                                        \
  62                 }                                                               \
  63                 prwlock = *rwlock;                                              \
  64         }
  65
  66 /*
  67  * Prototypes
  68  */
  69
  70 static int
  71 rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
  72 {
  73         pthread_rwlock_t prwlock;
  74
  75         if (attr == NULL || *attr == NULL ||
  76             (*attr)->pshared == PTHREAD_PROCESS_PRIVATE) {
  77                 prwlock = calloc(1, sizeof(struct pthread_rwlock));
  78                 if (prwlock == NULL)
  79                         return (ENOMEM);
  80                 *rwlock = prwlock;
  81         } else {
  82                 prwlock = __thr_pshared_offpage(rwlock, 1);
  83                 if (prwlock == NULL)
  84                         return (EFAULT);
  85                 prwlock->lock.rw_flags |= USYNC_PROCESS_SHARED;
  86                 *rwlock = THR_PSHARED_PTR;
  87         }
  88         return (0);
  89 }
  90
  91 int
  92 _pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
  93 {
  94         pthread_rwlock_t prwlock;
  95         int ret;
  96
  97         prwlock = *rwlock;
  98         if (prwlock == THR_RWLOCK_INITIALIZER)
  99                 ret = 0;
 100         else if (prwlock == THR_RWLOCK_DESTROYED)
 101                 ret = EINVAL;
 102         else if (prwlock == THR_PSHARED_PTR) {
 103                 *rwlock = THR_RWLOCK_DESTROYED;
 104                 __thr_pshared_destroy(rwlock);
 105                 ret = 0;
 106         } else {
 107                 *rwlock = THR_RWLOCK_DESTROYED;
 108                 free(prwlock);
 109                 ret = 0;
 110         }
 111         return (ret);
 112 }
 113
 114 static int
 115 init_static(struct pthread *thread, pthread_rwlock_t *rwlock)
 116 {
 117         int ret;
 118
 119         THR_LOCK_ACQUIRE(thread, &_rwlock_static_lock);
 120
 121         if (*rwlock == THR_RWLOCK_INITIALIZER)
 122                 ret = rwlock_init(rwlock, NULL);
 123         else
 124                 ret = 0;
 125
 126         THR_LOCK_RELEASE(thread, &_rwlock_static_lock);
 127
 128         return (ret);
 129 }
 130
 131 int
 132 _pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
 133 {
 134
 135         *rwlock = NULL;
 136         return (rwlock_init(rwlock, attr));
 137 }
 138
 139 static int
 140 rwlock_rdlock_common(pthread_rwlock_t *rwlock, const struct timespec *abstime)
 141 {
 142         struct pthread *curthread = _get_curthread();
 143         pthread_rwlock_t prwlock;
 144         int flags;
 145         int ret;
 146
 147         CHECK_AND_INIT_RWLOCK
 148
 149         if (curthread->rdlock_count) {
 150                 /*
 151                  * To avoid having to track all the rdlocks held by
 152                  * a thread or all of the threads that hold a rdlock,
 153                  * we keep a simple count of all the rdlocks held by
 154                  * a thread.  If a thread holds any rdlocks it is
 155                  * possible that it is attempting to take a recursive
 156                  * rdlock.  If there are blocked writers and precedence
 157                  * is given to them, then that would result in the thread
 158                  * deadlocking.  So allowing a thread to take the rdlock
 159                  * when it already has one or more rdlocks avoids the
 160                  * deadlock.  I hope the reader can follow that logic ;-)
 161                  */
 162                 flags = URWLOCK_PREFER_READER;
 163         } else {
 164                 flags = 0;
 165         }
 166
 167         /*
 168          * POSIX said the validity of the abstimeout parameter need
 169          * not be checked if the lock can be immediately acquired.
 170          */
 171         ret = _thr_rwlock_tryrdlock(&prwlock->lock, flags);
 172         if (ret == 0) {
 173                 curthread->rdlock_count++;
 174                 return (ret);
 175         }
 176
 177         if (__predict_false(abstime &&
 178                 (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
 179                 return (EINVAL);
 180
 181         for (;;) {
 182                 /* goto kernel and lock it */
 183                 ret = __thr_rwlock_rdlock(&prwlock->lock, flags, abstime);
 184                 if (ret != EINTR)
 185                         break;
 186
 187                 /* if interrupted, try to lock it in userland again. */
 188                 if (_thr_rwlock_tryrdlock(&prwlock->lock, flags) == 0) {
 189                         ret = 0;
 190                         break;
 191                 }
 192         }
 193         if (ret == 0)
 194                 curthread->rdlock_count++;
 195         return (ret);
 196 }
 197
 198 int
 199 _pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
 200 {
 201         return (rwlock_rdlock_common(rwlock, NULL));
 202 }
 203
 204 int
 205 _pthread_rwlock_timedrdlock (pthread_rwlock_t *rwlock,
 206          const struct timespec *abstime)
 207 {
 208         return (rwlock_rdlock_common(rwlock, abstime));
 209 }
 210
 211 int
 212 _pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
 213 {
 214         struct pthread *curthread = _get_curthread();
 215         pthread_rwlock_t prwlock;
 216         int flags;
 217         int ret;
 218
 219         CHECK_AND_INIT_RWLOCK
 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         CHECK_AND_INIT_RWLOCK
 253
 254         ret = _thr_rwlock_trywrlock(&prwlock->lock);
 255         if (ret == 0)
 256                 prwlock->owner = TID(curthread);
 257         return (ret);
 258 }
 259
 260 static int
 261 rwlock_wrlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
 262 {
 263         struct pthread *curthread = _get_curthread();
 264         pthread_rwlock_t prwlock;
 265         int ret;
 266
 267         CHECK_AND_INIT_RWLOCK
 268
 269         /*
 270          * POSIX said the validity of the abstimeout parameter need
 271          * not be checked if the lock can be immediately acquired.
 272          */
 273         ret = _thr_rwlock_trywrlock(&prwlock->lock);
 274         if (ret == 0) {
 275                 prwlock->owner = TID(curthread);
 276                 return (ret);
 277         }
 278
 279         if (__predict_false(abstime &&
 280             (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
 281                 return (EINVAL);
 282
 283         for (;;) {
 284                 /* goto kernel and lock it */
 285                 ret = __thr_rwlock_wrlock(&prwlock->lock, abstime);
 286                 if (ret == 0) {
 287                         prwlock->owner = TID(curthread);
 288                         break;
 289                 }
 290
 291                 if (ret != EINTR)
 292                         break;
 293
 294                 /* if interrupted, try to lock it in userland again. */
 295                 if (_thr_rwlock_trywrlock(&prwlock->lock) == 0) {
 296                         ret = 0;
 297                         prwlock->owner = TID(curthread);
 298                         break;
 299                 }
 300         }
 301         return (ret);
 302 }
 303
 304 int
 305 _pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
 306 {
 307         return (rwlock_wrlock_common (rwlock, NULL));
 308 }
 309
 310 int
 311 _pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
 312     const struct timespec *abstime)
 313 {
 314         return (rwlock_wrlock_common (rwlock, abstime));
 315 }
 316
 317 int
 318 _pthread_rwlock_unlock(pthread_rwlock_t *rwlock)
 319 {
 320         struct pthread *curthread = _get_curthread();
 321         pthread_rwlock_t prwlock;
 322         int ret;
 323         int32_t state;
 324
 325         if (*rwlock == THR_PSHARED_PTR) {
 326                 prwlock = __thr_pshared_offpage(rwlock, 0);
 327                 if (prwlock == NULL)
 328                         return (EINVAL);
 329         } else {
 330                 prwlock = *rwlock;
 331         }
 332
 333         if (__predict_false(prwlock <= THR_RWLOCK_DESTROYED))
 334                 return (EINVAL);
 335
 336         state = prwlock->lock.rw_state;
 337         if (state & URWLOCK_WRITE_OWNER) {
 338                 if (__predict_false(prwlock->owner != TID(curthread)))
 339                         return (EPERM);
 340                 prwlock->owner = 0;
 341         }
 342
 343         ret = _thr_rwlock_unlock(&prwlock->lock);
 344         if (ret == 0 && (state & URWLOCK_WRITE_OWNER) == 0)
 345                 curthread->rdlock_count--;
 346
 347         return (ret);
 348 }