Commit 685ac18a authored by Rémi Denis-Courmont's avatar Rémi Denis-Courmont
Browse files

Add vlc_mutex_trylock

parent 9fc77f32
......@@ -143,6 +143,7 @@ VLC_EXPORT( int, vlc_mutex_init, ( vlc_mutex_t * ) );
VLC_EXPORT( int, vlc_mutex_init_recursive, ( vlc_mutex_t * ) );
VLC_EXPORT( void, vlc_mutex_destroy, ( vlc_mutex_t * ) );
VLC_EXPORT( void, vlc_mutex_lock, ( vlc_mutex_t * ) );
VLC_EXPORT( int, vlc_mutex_trylock, ( vlc_mutex_t * ) );
VLC_EXPORT( void, vlc_mutex_unlock, ( vlc_mutex_t * ) );
VLC_EXPORT( int, vlc_cond_init, ( vlc_cond_t * ) );
VLC_EXPORT( void, vlc_cond_destroy, ( vlc_cond_t * ) );
......
......@@ -458,6 +458,7 @@ vlc_mutex_destroy
vlc_mutex_init
vlc_mutex_init_recursive
vlc_mutex_lock
vlc_mutex_trylock
vlc_mutex_unlock
__vlc_object_attach
__vlc_object_create
......
......@@ -356,6 +356,7 @@ void vlc_mutex_destroy (vlc_mutex_t *p_mutex)
* Acquires a mutex. If needed, waits for any other thread to release it.
* Beware of deadlocks when locking multiple mutexes at the same time,
* or when using mutexes from callbacks.
* This function is not a cancellation-point.
*
* @param p_mutex mutex initialized with vlc_mutex_init() or
* vlc_mutex_init_recursive()
......@@ -383,6 +384,46 @@ void vlc_mutex_lock (vlc_mutex_t *p_mutex)
#endif
}
/**
* Acquires a mutex if and only if it is not currently held by another thread.
* This function never sleeps and can be used in delay-critical code paths.
* This function is not a cancellation-point.
*
* <b>Beware</b>: If this function fails, then the mutex is held... by another
* thread. The calling thread must deal with the error appropriately. That
* typically implies postponing the operations that would have required the
* mutex. If the thread cannot defer those operations, then it must use
* vlc_mutex_lock(). If in doubt, use vlc_mutex_lock() instead.
*
* @param p_mutex mutex initialized with vlc_mutex_init() or
* vlc_mutex_init_recursive()
* @return 0 if the mutex could be acquired, an error code otherwise.
*/
int vlc_mutex_trylock (vlc_mutex_t *p_mutex)
{
#if defined(LIBVLC_USE_PTHREAD)
int val = pthread_mutex_trylock( p_mutex );
if (val != EBUSY)
VLC_THREAD_ASSERT ("locking mutex");
return val;
#elif defined( WIN32 )
if (InterlockedCompareExchange (&p_mutex->initialized, 0, 0) == 0)
{ /* ^^ We could also lock super_mutex all the time... sluggish */
assert (p_mutex != &super_mutex); /* this one cannot be static */
vlc_mutex_lock (&super_mutex);
if (InterlockedCompareExchange (&p_mutex->initialized, 0, 0) == 0)
vlc_mutex_init (p_mutex);
/* FIXME: destroy the mutex some time... */
vlc_mutex_unlock (&super_mutex);
}
assert (InterlockedExchange (&p_mutex->initialized, 1) == 1);
return TryEnterCriticalSection (&p_mutex->mutex) ? 0 : EBUSY;
#endif
}
/**
* Releases a mutex (or crashes if the mutex is not locked by the caller).
......
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