src/misc/threads.c

   1 /*****************************************************************************
   2  * threads.c: LibVLC generic thread support
   3  *****************************************************************************
   4  * Copyright (C) 2009-2012 Rémi Denis-Courmont
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU Lesser General Public License as published by
   8  * the Free Software Foundation; either version 2.1 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  19  *****************************************************************************/
  20
  21 #ifdef HAVE_CONFIG_H
  22 # include "config.h"
  23 #endif
  24
  25 #include <assert.h>
  26
  27 #include <vlc_common.h>
  28
  29 /*** Global locks ***/
  30
  31 void vlc_global_mutex (unsigned n, bool acquire)
  32 {
  33     static vlc_mutex_t locks[] = {
  34         VLC_STATIC_MUTEX,
  35         VLC_STATIC_MUTEX,
  36         VLC_STATIC_MUTEX,
  37         VLC_STATIC_MUTEX,
  38         VLC_STATIC_MUTEX,
  39     };
  40     static_assert (VLC_MAX_MUTEX == (sizeof (locks) / sizeof (locks[0])),
  41                    "Wrong number of global mutexes");
  42     assert (n < (sizeof (locks) / sizeof (locks[0])));
  43
  44     vlc_mutex_t *lock = locks + n;
  45     if (acquire)
  46         vlc_mutex_lock (lock);
  47     else
  48         vlc_mutex_unlock (lock);
  49 }
  50
  51 #ifdef LIBVLC_NEED_RWLOCK
  52 /*** Generic read/write locks ***/
  53 #include <stdlib.h>
  54 #include <limits.h>
  55 /* NOTE:
  56  * lock->state is a signed long integer:
  57  *  - The sign bit is set when the lock is held for writing.
  58  *  - The other bits code the number of times the lock is held for reading.
  59  * Consequently:
  60  *  - The value is negative if and only if the lock is held for writing.
  61  *  - The value is zero if and only if the lock is not held at all.
  62  */
  63 #define READER_MASK LONG_MAX
  64 #define WRITER_BIT  LONG_MIN
  65
  66 void vlc_rwlock_init (vlc_rwlock_t *lock)
  67 {
  68     vlc_mutex_init (&lock->mutex);
  69     vlc_cond_init (&lock->wait);
  70     lock->state = 0;
  71 }
  72
  73 void vlc_rwlock_destroy (vlc_rwlock_t *lock)
  74 {
  75     vlc_cond_destroy (&lock->wait);
  76     vlc_mutex_destroy (&lock->mutex);
  77 }
  78
  79 void vlc_rwlock_rdlock (vlc_rwlock_t *lock)
  80 {
  81     vlc_mutex_lock (&lock->mutex);
  82     /* Recursive read-locking is allowed.
  83      * Ensure that there is no active writer. */
  84     while (lock->state < 0)
  85     {
  86         assert (lock->state == WRITER_BIT);
  87         mutex_cleanup_push (&lock->mutex);
  88         vlc_cond_wait (&lock->wait, &lock->mutex);
  89         vlc_cleanup_pop ();
  90     }
  91     if (unlikely(lock->state >= READER_MASK))
  92         abort (); /* An overflow is certainly a recursion bug. */
  93     lock->state++;
  94     vlc_mutex_unlock (&lock->mutex);
  95 }
  96
  97 void vlc_rwlock_wrlock (vlc_rwlock_t *lock)
  98 {
  99     vlc_mutex_lock (&lock->mutex);
 100     /* Wait until nobody owns the lock in any way. */
 101     while (lock->state != 0)
 102     {
 103         mutex_cleanup_push (&lock->mutex);
 104         vlc_cond_wait (&lock->wait, &lock->mutex);
 105         vlc_cleanup_pop ();
 106     }
 107     lock->state = WRITER_BIT;
 108     vlc_mutex_unlock (&lock->mutex);
 109 }
 110
 111 void vlc_rwlock_unlock (vlc_rwlock_t *lock)
 112 {
 113     vlc_mutex_lock (&lock->mutex);
 114     if (lock->state < 0)
 115     {   /* Write unlock */
 116         assert (lock->state == WRITER_BIT);
 117         /* Let reader and writer compete. OS scheduler decides who wins. */
 118         lock->state = 0;
 119         vlc_cond_broadcast (&lock->wait);
 120     }
 121     else
 122     {   /* Read unlock */
 123         assert (lock->state > 0);
 124         /* If there are no readers left, wake up one pending writer. */
 125         if (--lock->state == 0)
 126             vlc_cond_signal (&lock->wait);
 127     }
 128     vlc_mutex_unlock (&lock->mutex);
 129 }
 130 #endif /* LIBVLC_NEED_RWLOCK */
 131
 132 #ifdef LIBVLC_NEED_SEMAPHORE
 133 /*** Generic semaphores ***/
 134 #include <limits.h>
 135 #include <errno.h>
 136
 137 void vlc_sem_init (vlc_sem_t *sem, unsigned value)
 138 {
 139     vlc_mutex_init (&sem->lock);
 140     vlc_cond_init (&sem->wait);
 141     sem->value = value;
 142 }
 143
 144 void vlc_sem_destroy (vlc_sem_t *sem)
 145 {
 146     vlc_cond_destroy (&sem->wait);
 147     vlc_mutex_destroy (&sem->lock);
 148 }
 149
 150 int vlc_sem_post (vlc_sem_t *sem)
 151 {
 152     int ret = 0;
 153
 154     vlc_mutex_lock (&sem->lock);
 155     if (likely(sem->value != UINT_MAX))
 156         sem->value++;
 157     else
 158         ret = EOVERFLOW;
 159     vlc_mutex_unlock (&sem->lock);
 160     vlc_cond_signal (&sem->wait);
 161
 162     return ret;
 163 }
 164
 165 void vlc_sem_wait (vlc_sem_t *sem)
 166 {
 167     vlc_mutex_lock (&sem->lock);
 168     mutex_cleanup_push (&sem->lock);
 169     while (!sem->value)
 170         vlc_cond_wait (&sem->wait, &sem->lock);
 171     sem->value--;
 172     vlc_cleanup_pop ();
 173     vlc_mutex_unlock (&sem->lock);
 174 }
 175 #endif /* LIBVLC_NEED_SEMAPHORE */