linuxthreads/rwlock.c

   1 /* Read-write lock implementation.
   2    Copyright (C) 1998 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Xavier Leroy <Xavier.Leroy@inria.fr>
   5    and Ulrich Drepper <drepper@cygnus.com>, 1998.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Library General Public License as
   9    published by the Free Software Foundation; either version 2 of the
  10    License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Library General Public License for more details.
  16
  17    You should have received a copy of the GNU Library General Public
  18    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  19    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA.  */
  21
  22 #include <errno.h>
  23 #include <pthread.h>
  24 #include "internals.h"
  25 #include "queue.h"
  26 #include "restart.h"
  27 #include "spinlock.h"
  28
  29 int
  30 pthread_rwlock_init (pthread_rwlock_t *rwlock,
  31                      const pthread_rwlockattr_t *attr)
  32 {
  33   rwlock->rw_spinlock = 0;
  34   rwlock->rw_readers = 0;
  35   rwlock->rw_writer = NULL;
  36
  37   queue_init(&rwlock->rw_read_waiting);
  38   queue_init(&rwlock->rw_write_waiting);
  39
  40   if (attr == NULL)
  41     {
  42       rwlock->rw_kind = PTHREAD_RWLOCK_DEFAULT_NP;
  43       rwlock->rw_pshared = PTHREAD_PROCESS_PRIVATE;
  44     }
  45   else
  46     {
  47       rwlock->rw_kind = attr->lockkind;
  48       rwlock->rw_pshared = attr->pshared;
  49     }
  50
  51   return 0;
  52 }
  53
  54
  55 int
  56 pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
  57 {
  58   int readers;
  59   _pthread_descr writer;
  60
  61   acquire (&rwlock->rw_spinlock);
  62   readers = rwlock->rw_readers;
  63   writer = rwlock->rw_writer;
  64   release (&rwlock->rw_spinlock);
  65
  66   if (readers > 0 || writer != NULL)
  67     return EBUSY;
  68
  69   return 0;
  70 }
  71
  72
  73 int
  74 pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
  75 {
  76   pthread_descr self;
  77
  78   while (1)
  79     {
  80       acquire (&rwlock->rw_spinlock);
  81       if (rwlock->rw_writer == NULL
  82           || (rwlock->rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP
  83               && rwlock->rw_readers != 0))
  84         /* We can add a reader lock.  */
  85         break;
  86
  87       /* Suspend ourselves, then try again */
  88       self = thread_self ();
  89       enqueue (&rwlock->rw_read_waiting, self);
  90       release (&rwlock->rw_spinlock);
  91       suspend (self); /* This is not a cancellation point */
  92     }
  93
  94   ++rwlock->rw_readers;
  95   release (&rwlock->rw_spinlock);
  96
  97   return 0;
  98 }
  99
 100
 101 int
 102 pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
 103 {
 104   int result = EBUSY;
 105
 106   acquire (&rwlock->rw_spinlock);
 107   if (rwlock->rw_writer == NULL
 108       || (rwlock->rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP
 109           && rwlock->rw_readers != 0))
 110     {
 111       ++rwlock->rw_readers;
 112       result = 0;
 113     }
 114   release (&rwlock->rw_spinlock);
 115
 116   return result;
 117 }
 118
 119
 120 int
 121 pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
 122 {
 123   pthread_descr self = thread_self ();
 124
 125   while(1)
 126     {
 127       acquire (&rwlock->rw_spinlock);
 128       if (rwlock->rw_readers == 0 && rwlock->rw_writer == NULL)
 129         {
 130           rwlock->rw_writer = self;
 131           release (&rwlock->rw_spinlock);
 132           return 0;
 133         }
 134
 135       /* Suspend ourselves, then try again */
 136       enqueue (&rwlock->rw_write_waiting, self);
 137       release (&rwlock->rw_spinlock);
 138       suspend (self); /* This is not a cancellation point */
 139     }
 140 }
 141
 142
 143 int
 144 pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
 145 {
 146   int result = EBUSY;
 147
 148   acquire (&rwlock->rw_spinlock);
 149   if (rwlock->rw_readers == 0 && rwlock->rw_writer == NULL)
 150     {
 151       rwlock->rw_writer = thread_self ();
 152       result = 0;
 153     }
 154   release (&rwlock->rw_spinlock);
 155
 156   return result;
 157 }
 158
 159
 160 int
 161 pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
 162 {
 163   struct _pthread_queue torestart;
 164   pthread_descr th;
 165
 166   acquire (&rwlock->rw_spinlock);
 167   if (rwlock->rw_writer != NULL)
 168     {
 169       /* Unlocking a write lock.  */
 170       if (rwlock->rw_writer != thread_self ())
 171         {
 172           release (&rwlock->rw_spinlock);
 173           return EPERM;
 174         }
 175       rwlock->rw_writer = NULL;
 176
 177       if (rwlock->rw_kind == PTHREAD_RWLOCK_PREFER_READER_NP
 178           || (th = dequeue (&rwlock->rw_write_waiting)) == NULL)
 179         {
 180           /* Restart all waiting readers.  */
 181           torestart = rwlock->rw_read_waiting;
 182           queue_init (&rwlock->rw_read_waiting);
 183           release (&rwlock->rw_spinlock);
 184           while ((th = dequeue (&torestart)) != NULL)
 185             restart (th);
 186         }
 187       else
 188         {
 189           /* Restart one waiting writer.  */
 190           release (&rwlock->rw_spinlock);
 191           restart (th);
 192         }
 193     }
 194   else
 195     {
 196       /* Unlocking a read lock.  */
 197       if (rwlock->rw_readers == 0)
 198         {
 199           release (&rwlock->rw_spinlock);
 200           return EPERM;
 201         }
 202
 203       --rwlock->rw_readers;
 204       if (rwlock->rw_readers == 0)
 205         /* Restart one waiting writer, if any.  */
 206         th = dequeue (&rwlock->rw_write_waiting);
 207       else
 208         th = NULL;
 209
 210       release (&rwlock->rw_spinlock);
 211       if (th != NULL)
 212         restart (th);
 213     }
 214
 215   return 0;
 216 }
 217
 218
 219
 220 int
 221 pthread_rwlockattr_init (pthread_rwlockattr_t *attr)
 222 {
 223   attr->lockkind = 0;
 224   attr->pshared = 0;
 225
 226   return 0;
 227 }
 228
 229
 230 int
 231 pthread_rwlockattr_destroy (pthread_rwlockattr_t *attr)
 232 {
 233   return 0;
 234 }
 235
 236
 237 int
 238 pthread_rwlockattr_getpshared (const pthread_rwlockattr_t *attr, int *pshared)
 239 {
 240   *pshared = attr->pshared;
 241   return 0;
 242 }
 243
 244
 245 int
 246 pthread_rwlockattr_setpshared (pthread_rwlockattr_t *attr, int pshared)
 247 {
 248   if (pshared != PTHREAD_PROCESS_PRIVATE && pshared != PTHREAD_PROCESS_SHARED)
 249     return EINVAL;
 250
 251   attr->pshared = pshared;
 252
 253   return 0;
 254 }
 255
 256
 257 int
 258 pthread_rwlockattr_getkind_np (const pthread_rwlockattr_t *attr, int *pref)
 259 {
 260   *pref = attr->lockkind;
 261   return 0;
 262 }
 263
 264
 265 int
 266 pthread_rwlockattr_setkind_np (pthread_rwlockattr_t *attr, int pref)
 267 {
 268   if (pref != PTHREAD_RWLOCK_PREFER_READER_NP
 269       && pref != PTHREAD_RWLOCK_PREFER_WRITER_NP
 270       && pref != PTHREAD_RWLOCK_DEFAULT_NP)
 271     return EINVAL;
 272
 273   attr->lockkind = pref;
 274
 275   return 0;
 276 }