Commit 53ffb224 authored by Rémi Denis-Courmont's avatar Rémi Denis-Courmont

Win32 R/W locks: fix/add comments, add asserts

parent 1b6caac9
......@@ -392,13 +392,10 @@ void vlc_rwlock_init (vlc_rwlock_t *lock)
vlc_cond_init (&lock->read_wait);
vlc_cond_init (&lock->write_wait);
lock->readers = 0; /* active readers */
lock->writers = 0; /* waiting or active writers */
lock->writers = 0; /* waiting writers */
lock->writer = 0; /* ID of active writer */
}
/**
* Destroys an initialized unused read/write lock.
*/
void vlc_rwlock_destroy (vlc_rwlock_t *lock)
{
vlc_cond_destroy (&lock->read_wait);
......@@ -406,57 +403,78 @@ void vlc_rwlock_destroy (vlc_rwlock_t *lock)
vlc_mutex_destroy (&lock->mutex);
}
/**
* Acquires a read/write lock for reading. Recursion is allowed.
*/
void vlc_rwlock_rdlock (vlc_rwlock_t *lock)
{
vlc_mutex_lock (&lock->mutex);
/* Recursive read-locking is allowed. With the infos available:
* - the loosest possible condition (no active writer) is:
* (lock->writer != 0)
* - the strictest possible condition is:
* (lock->writer != 0 || (lock->readers == 0 && lock->writers > 0))
* or (lock->readers == 0 && (lock->writer != 0 || lock->writers > 0))
*/
while (lock->writer != 0)
{
assert (lock->readers == 0);
vlc_cond_wait (&lock->read_wait, &lock->mutex);
if (lock->readers == ULONG_MAX)
}
if (unlikely(lock->readers == ULONG_MAX))
abort ();
lock->readers++;
vlc_mutex_unlock (&lock->mutex);
}
/**
* Acquires a read/write lock for writing. Recursion is not allowed.
*/
static void vlc_rwlock_rdunlock (vlc_rwlock_t *lock)
{
vlc_mutex_lock (&lock->mutex);
assert (lock->readers > 0);
/* If there are no readers left, wake up a writer. */
if (--lock->readers == 0 && lock->writers > 0)
vlc_cond_signal (&lock->write_wait);
vlc_mutex_unlock (&lock->mutex);
}
void vlc_rwlock_wrlock (vlc_rwlock_t *lock)
{
vlc_mutex_lock (&lock->mutex);
if (lock->writers == ULONG_MAX)
if (unlikely(lock->writers == ULONG_MAX))
abort ();
lock->writers++;
/* Wait until nobody owns the lock in either way. */
while ((lock->readers > 0) || (lock->writer != 0))
vlc_cond_wait (&lock->write_wait, &lock->mutex);
lock->writers--;
assert (lock->writer == 0);
lock->writer = GetCurrentThreadId ();
vlc_mutex_unlock (&lock->mutex);
}
/**
* Releases a read/write lock.
*/
void vlc_rwlock_unlock (vlc_rwlock_t *lock)
static void vlc_rwlock_wrunlock (vlc_rwlock_t *lock)
{
vlc_mutex_lock (&lock->mutex);
if (lock->readers > 0)
lock->readers--; /* Read unlock */
else
lock->writer = 0; /* Write unlock */
assert (lock->writer == GetCurrentThreadId ());
assert (lock->readers == 0);
lock->writer = 0; /* Write unlock */
/* Let reader and writer compete. Scheduler decides who wins. */
if (lock->writers > 0)
{
if (lock->readers == 0)
vlc_cond_signal (&lock->write_wait);
}
else
vlc_cond_broadcast (&lock->read_wait);
vlc_cond_signal (&lock->write_wait);
vlc_cond_broadcast (&lock->read_wait);
vlc_mutex_unlock (&lock->mutex);
}
void vlc_rwlock_unlock (vlc_rwlock_t *lock)
{
/* Note: If the lock is held for reading, lock->writer is nul.
* If the lock is held for writing, only this thread can store a value to
* lock->writer. Either way, lock->writer is safe to fetch here. */
if (lock->writer != 0)
vlc_rwlock_wrunlock (lock);
else
vlc_rwlock_rdunlock (lock);
}
/*** Thread-specific variables (TLS) ***/
struct vlc_threadvar
{
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment