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         VLC_STATIC_MUTEX,
  40     };
  41     static_assert (VLC_MAX_MUTEX == (sizeof (locks) / sizeof (locks[0])),
  42                    "Wrong number of global mutexes");
  43     assert (n < (sizeof (locks) / sizeof (locks[0])));
  44
  45     vlc_mutex_t *lock = locks + n;
  46     if (acquire)
  47         vlc_mutex_lock (lock);
  48     else
  49         vlc_mutex_unlock (lock);
  50 }
  51
  52 #ifdef LIBVLC_NEED_RWLOCK
  53 /*** Generic read/write locks ***/
  54 #include <stdlib.h>
  55 #include <limits.h>
  56 /* NOTE:
  57  * lock->state is a signed long integer:
  58  *  - The sign bit is set when the lock is held for writing.
  59  *  - The other bits code the number of times the lock is held for reading.
  60  * Consequently:
  61  *  - The value is negative if and only if the lock is held for writing.
  62  *  - The value is zero if and only if the lock is not held at all.
  63  */
  64 #define READER_MASK LONG_MAX
  65 #define WRITER_BIT  LONG_MIN
  66
  67 void vlc_rwlock_init (vlc_rwlock_t *lock)
  68 {
  69     vlc_mutex_init (&lock->mutex);
  70     vlc_cond_init (&lock->wait);
  71     lock->state = 0;
  72 }
  73
  74 void vlc_rwlock_destroy (vlc_rwlock_t *lock)
  75 {
  76     vlc_cond_destroy (&lock->wait);
  77     vlc_mutex_destroy (&lock->mutex);
  78 }
  79
  80 void vlc_rwlock_rdlock (vlc_rwlock_t *lock)
  81 {
  82     vlc_mutex_lock (&lock->mutex);
  83     /* Recursive read-locking is allowed.
  84      * Ensure that there is no active writer. */
  85     while (lock->state < 0)
  86     {
  87         assert (lock->state == WRITER_BIT);
  88         mutex_cleanup_push (&lock->mutex);
  89         vlc_cond_wait (&lock->wait, &lock->mutex);
  90         vlc_cleanup_pop ();
  91     }
  92     if (unlikely(lock->state >= READER_MASK))
  93         abort (); /* An overflow is certainly a recursion bug. */
  94     lock->state++;
  95     vlc_mutex_unlock (&lock->mutex);
  96 }
  97
  98 void vlc_rwlock_wrlock (vlc_rwlock_t *lock)
  99 {
 100     vlc_mutex_lock (&lock->mutex);
 101     /* Wait until nobody owns the lock in any way. */
 102     while (lock->state != 0)
 103     {
 104         mutex_cleanup_push (&lock->mutex);
 105         vlc_cond_wait (&lock->wait, &lock->mutex);
 106         vlc_cleanup_pop ();
 107     }
 108     lock->state = WRITER_BIT;
 109     vlc_mutex_unlock (&lock->mutex);
 110 }
 111
 112 void vlc_rwlock_unlock (vlc_rwlock_t *lock)
 113 {
 114     vlc_mutex_lock (&lock->mutex);
 115     if (lock->state < 0)
 116     {   /* Write unlock */
 117         assert (lock->state == WRITER_BIT);
 118         /* Let reader and writer compete. OS scheduler decides who wins. */
 119         lock->state = 0;
 120         vlc_cond_broadcast (&lock->wait);
 121     }
 122     else
 123     {   /* Read unlock */
 124         assert (lock->state > 0);
 125         /* If there are no readers left, wake up one pending writer. */
 126         if (--lock->state == 0)
 127             vlc_cond_signal (&lock->wait);
 128     }
 129     vlc_mutex_unlock (&lock->mutex);
 130 }
 131 #endif /* LIBVLC_NEED_RWLOCK */
 132
 133 #ifdef LIBVLC_NEED_SEMAPHORE
 134 /*** Generic semaphores ***/
 135 #include <limits.h>
 136 #include <errno.h>
 137
 138 void vlc_sem_init (vlc_sem_t *sem, unsigned value)
 139 {
 140     vlc_mutex_init (&sem->lock);
 141     vlc_cond_init (&sem->wait);
 142     sem->value = value;
 143 }
 144
 145 void vlc_sem_destroy (vlc_sem_t *sem)
 146 {
 147     vlc_cond_destroy (&sem->wait);
 148     vlc_mutex_destroy (&sem->lock);
 149 }
 150
 151 int vlc_sem_post (vlc_sem_t *sem)
 152 {
 153     int ret = 0;
 154
 155     vlc_mutex_lock (&sem->lock);
 156     if (likely(sem->value != UINT_MAX))
 157         sem->value++;
 158     else
 159         ret = EOVERFLOW;
 160     vlc_mutex_unlock (&sem->lock);
 161     vlc_cond_signal (&sem->wait);
 162
 163     return ret;
 164 }
 165
 166 void vlc_sem_wait (vlc_sem_t *sem)
 167 {
 168     vlc_mutex_lock (&sem->lock);
 169     mutex_cleanup_push (&sem->lock);
 170     while (!sem->value)
 171         vlc_cond_wait (&sem->wait, &sem->lock);
 172     sem->value--;
 173     vlc_cleanup_run ();
 174 }
 175 #endif /* LIBVLC_NEED_SEMAPHORE */