src/misc/threads.c

   1 /*****************************************************************************
   2  * threads.c: LibVLC generic thread support
   3  *****************************************************************************
   4  * Copyright (C) 2009-2016 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 #include <errno.h>
  27
  28 #include <vlc_common.h>
  29
  30 /*** Global locks ***/
  31
  32 void vlc_global_mutex (unsigned n, bool acquire)
  33 {
  34     static vlc_mutex_t locks[] = {
  35         VLC_STATIC_MUTEX,
  36         VLC_STATIC_MUTEX,
  37         VLC_STATIC_MUTEX,
  38         VLC_STATIC_MUTEX,
  39         VLC_STATIC_MUTEX,
  40 #ifdef _WIN32
  41         VLC_STATIC_MUTEX, // For MTA holder
  42 #endif
  43     };
  44     static_assert (VLC_MAX_MUTEX == (sizeof (locks) / sizeof (locks[0])),
  45                    "Wrong number of global mutexes");
  46     assert (n < (sizeof (locks) / sizeof (locks[0])));
  47
  48     vlc_mutex_t *lock = locks + n;
  49     if (acquire)
  50         vlc_mutex_lock (lock);
  51     else
  52         vlc_mutex_unlock (lock);
  53 }
  54
  55 #if defined (_WIN32) && (_WIN32_WINNT < _WIN32_WINNT_WIN8)
  56 /* Cannot define OS version-dependent stuff in public headers */
  57 # undef LIBVLC_NEED_SLEEP
  58 # undef LIBVLC_NEED_SEMAPHORE
  59 #endif
  60
  61 #if defined(LIBVLC_NEED_SLEEP) || defined(LIBVLC_NEED_CONDVAR)
  62 #include <stdatomic.h>
  63
  64 static void vlc_cancel_addr_prepare(void *addr)
  65 {
  66     /* Let thread subsystem on address to broadcast for cancellation */
  67     vlc_cancel_addr_set(addr);
  68     vlc_cleanup_push(vlc_cancel_addr_clear, addr);
  69     /* Check if cancellation was pending before vlc_cancel_addr_set() */
  70     vlc_testcancel();
  71     vlc_cleanup_pop();
  72 }
  73
  74 static void vlc_cancel_addr_finish(void *addr)
  75 {
  76     vlc_cancel_addr_clear(addr);
  77     /* Act on cancellation as potential wake-up source */
  78     vlc_testcancel();
  79 }
  80 #endif
  81
  82 #ifdef LIBVLC_NEED_SLEEP
  83 void (mwait)(mtime_t deadline)
  84 {
  85     mtime_t delay;
  86     atomic_int value = ATOMIC_VAR_INIT(0);
  87
  88     vlc_cancel_addr_prepare(&value);
  89
  90     while ((delay = (deadline - mdate())) > 0)
  91     {
  92         vlc_addr_timedwait(&value, 0, delay);
  93         vlc_testcancel();
  94     }
  95
  96     vlc_cancel_addr_finish(&value);
  97 }
  98
  99 void (msleep)(mtime_t delay)
 100 {
 101     mwait(mdate() + delay);
 102 }
 103 #endif
 104
 105 #ifdef LIBVLC_NEED_CONDVAR
 106 #include <stdalign.h>
 107
 108 static inline atomic_uint *vlc_cond_value(vlc_cond_t *cond)
 109 {
 110     /* XXX: ugly but avoids including stdatomic.h in vlc_threads.h */
 111     static_assert (sizeof (cond->value) <= sizeof (atomic_uint),
 112                    "Size mismatch!");
 113     static_assert ((alignof (cond->value) % alignof (atomic_uint)) == 0,
 114                    "Alignment mismatch");
 115     return (atomic_uint *)&cond->value;
 116 }
 117
 118 void vlc_cond_init(vlc_cond_t *cond)
 119 {
 120     /* Initial value is irrelevant but set it for happy debuggers */
 121     atomic_init(vlc_cond_value(cond), 0);
 122 }
 123
 124 void vlc_cond_init_daytime(vlc_cond_t *cond)
 125 {
 126     vlc_cond_init(cond);
 127 }
 128
 129 void vlc_cond_destroy(vlc_cond_t *cond)
 130 {
 131     /* Tempting sanity check but actually incorrect:
 132     assert((atomic_load_explicit(vlc_cond_value(cond),
 133                                  memory_order_relaxed) & 1) == 0);
 134      * Due to timeouts and spurious wake-ups, the futex value can look like
 135      * there are waiters, even though there are none. */
 136     (void) cond;
 137 }
 138
 139 void vlc_cond_signal(vlc_cond_t *cond)
 140 {
 141     /* Probably the best documented approach is that of Bionic: increment
 142      * the futex here, and simply load the value in cnd_wait(). This has a bug
 143      * as unlikely as well-known: signals get lost if the futex is incremented
 144      * an exact multiple of 2^(CHAR_BIT * sizeof (int)) times.
 145      *
 146      * A different presumably bug-free solution is used here:
 147      * - cnd_signal() sets the futex to the equal-or-next odd value, while
 148      * - cnd_wait() sets the futex to the equal-or-next even value.
 149      **/
 150     atomic_fetch_or_explicit(vlc_cond_value(cond), 1, memory_order_relaxed);
 151     vlc_addr_signal(&cond->value);
 152 }
 153
 154 void vlc_cond_broadcast(vlc_cond_t *cond)
 155 {
 156     atomic_fetch_or_explicit(vlc_cond_value(cond), 1, memory_order_relaxed);
 157     vlc_addr_broadcast(&cond->value);
 158 }
 159
 160 void vlc_cond_wait(vlc_cond_t *cond, vlc_mutex_t *mutex)
 161 {
 162     unsigned value = atomic_load_explicit(vlc_cond_value(cond),
 163                                      memory_order_relaxed);
 164     while (value & 1)
 165     {
 166         if (atomic_compare_exchange_weak_explicit(vlc_cond_value(cond), &value,
 167                                                   value + 1,
 168                                                   memory_order_relaxed,
 169                                                   memory_order_relaxed))
 170             value++;
 171     }
 172
 173     vlc_cancel_addr_prepare(&cond->value);
 174     vlc_mutex_unlock(mutex);
 175
 176     vlc_addr_wait(&cond->value, value);
 177
 178     vlc_mutex_lock(mutex);
 179     vlc_cancel_addr_finish(&cond->value);
 180 }
 181
 182 static int vlc_cond_wait_delay(vlc_cond_t *cond, vlc_mutex_t *mutex,
 183                                mtime_t delay)
 184 {
 185     unsigned value = atomic_load_explicit(vlc_cond_value(cond),
 186                                           memory_order_relaxed);
 187     while (value & 1)
 188     {
 189         if (atomic_compare_exchange_weak_explicit(vlc_cond_value(cond), &value,
 190                                                   value + 1,
 191                                                   memory_order_relaxed,
 192                                                   memory_order_relaxed))
 193             value++;
 194     }
 195
 196     vlc_cancel_addr_prepare(&cond->value);
 197     vlc_mutex_unlock(mutex);
 198
 199     if (delay > 0)
 200         value = vlc_addr_timedwait(&cond->value, value, delay);
 201     else
 202         value = 0;
 203
 204     vlc_mutex_lock(mutex);
 205     vlc_cancel_addr_finish(&cond->value);
 206
 207     return value ? 0 : ETIMEDOUT;
 208 }
 209
 210 int vlc_cond_timedwait(vlc_cond_t *cond, vlc_mutex_t *mutex, mtime_t deadline)
 211 {
 212     return vlc_cond_wait_delay(cond, mutex, deadline - mdate());
 213 }
 214
 215 int vlc_cond_timedwait_daytime(vlc_cond_t *cond, vlc_mutex_t *mutex,
 216                                time_t deadline)
 217 {
 218     struct timespec ts;
 219
 220     timespec_get(&ts, TIME_UTC);
 221     deadline -= ts.tv_sec * CLOCK_FREQ;
 222     deadline -= ts.tv_nsec / (1000000000 / CLOCK_FREQ);
 223
 224     return vlc_cond_wait_delay(cond, mutex, deadline);
 225 }
 226 #endif
 227
 228 #ifdef LIBVLC_NEED_RWLOCK
 229 /*** Generic read/write locks ***/
 230 #include <stdlib.h>
 231 #include <limits.h>
 232 /* NOTE:
 233  * lock->state is a signed long integer:
 234  *  - The sign bit is set when the lock is held for writing.
 235  *  - The other bits code the number of times the lock is held for reading.
 236  * Consequently:
 237  *  - The value is negative if and only if the lock is held for writing.
 238  *  - The value is zero if and only if the lock is not held at all.
 239  */
 240 #define READER_MASK LONG_MAX
 241 #define WRITER_BIT  LONG_MIN
 242
 243 void vlc_rwlock_init (vlc_rwlock_t *lock)
 244 {
 245     vlc_mutex_init (&lock->mutex);
 246     vlc_cond_init (&lock->wait);
 247     lock->state = 0;
 248 }
 249
 250 void vlc_rwlock_destroy (vlc_rwlock_t *lock)
 251 {
 252     vlc_cond_destroy (&lock->wait);
 253     vlc_mutex_destroy (&lock->mutex);
 254 }
 255
 256 void vlc_rwlock_rdlock (vlc_rwlock_t *lock)
 257 {
 258     vlc_mutex_lock (&lock->mutex);
 259     /* Recursive read-locking is allowed.
 260      * Ensure that there is no active writer. */
 261     while (lock->state < 0)
 262     {
 263         assert (lock->state == WRITER_BIT);
 264         mutex_cleanup_push (&lock->mutex);
 265         vlc_cond_wait (&lock->wait, &lock->mutex);
 266         vlc_cleanup_pop ();
 267     }
 268     if (unlikely(lock->state >= READER_MASK))
 269         abort (); /* An overflow is certainly a recursion bug. */
 270     lock->state++;
 271     vlc_mutex_unlock (&lock->mutex);
 272 }
 273
 274 void vlc_rwlock_wrlock (vlc_rwlock_t *lock)
 275 {
 276     vlc_mutex_lock (&lock->mutex);
 277     /* Wait until nobody owns the lock in any way. */
 278     while (lock->state != 0)
 279     {
 280         mutex_cleanup_push (&lock->mutex);
 281         vlc_cond_wait (&lock->wait, &lock->mutex);
 282         vlc_cleanup_pop ();
 283     }
 284     lock->state = WRITER_BIT;
 285     vlc_mutex_unlock (&lock->mutex);
 286 }
 287
 288 void vlc_rwlock_unlock (vlc_rwlock_t *lock)
 289 {
 290     vlc_mutex_lock (&lock->mutex);
 291     if (lock->state < 0)
 292     {   /* Write unlock */
 293         assert (lock->state == WRITER_BIT);
 294         /* Let reader and writer compete. OS scheduler decides who wins. */
 295         lock->state = 0;
 296         vlc_cond_broadcast (&lock->wait);
 297     }
 298     else
 299     {   /* Read unlock */
 300         assert (lock->state > 0);
 301         /* If there are no readers left, wake up one pending writer. */
 302         if (--lock->state == 0)
 303             vlc_cond_signal (&lock->wait);
 304     }
 305     vlc_mutex_unlock (&lock->mutex);
 306 }
 307 #endif /* LIBVLC_NEED_RWLOCK */
 308
 309 #ifdef LIBVLC_NEED_SEMAPHORE
 310 /*** Generic semaphores ***/
 311 #include <limits.h>
 312 #include <errno.h>
 313
 314 void vlc_sem_init (vlc_sem_t *sem, unsigned value)
 315 {
 316     vlc_mutex_init (&sem->lock);
 317     vlc_cond_init (&sem->wait);
 318     sem->value = value;
 319 }
 320
 321 void vlc_sem_destroy (vlc_sem_t *sem)
 322 {
 323     vlc_cond_destroy (&sem->wait);
 324     vlc_mutex_destroy (&sem->lock);
 325 }
 326
 327 int vlc_sem_post (vlc_sem_t *sem)
 328 {
 329     int ret = 0;
 330
 331     vlc_mutex_lock (&sem->lock);
 332     if (likely(sem->value != UINT_MAX))
 333         sem->value++;
 334     else
 335         ret = EOVERFLOW;
 336     vlc_mutex_unlock (&sem->lock);
 337     vlc_cond_signal (&sem->wait);
 338
 339     return ret;
 340 }
 341
 342 void vlc_sem_wait (vlc_sem_t *sem)
 343 {
 344     vlc_mutex_lock (&sem->lock);
 345     mutex_cleanup_push (&sem->lock);
 346     while (!sem->value)
 347         vlc_cond_wait (&sem->wait, &sem->lock);
 348     sem->value--;
 349     vlc_cleanup_pop ();
 350     vlc_mutex_unlock (&sem->lock);
 351 }
 352 #endif /* LIBVLC_NEED_SEMAPHORE */