/*!
* Release the lock. Used for both "readers" and "writers".
*/
void Unlock()
{
int prevCount = ATOMIC::OPS::Increment(&_count, -1);
if (prevCount == 0)
{
// If the count goes from 0 => -1, there is a waiting writer and
// this is the last reader. Wake up the waiting writer.
//
_waiterSemaphore.Set();
}
else if (prevCount == -1)
{
// If the count goes from -1 => -2, this is a writer. Reset '_count'
// and release the lock, which allows new readers or writers to
// acquire it.
//
_count = 0;
_lock.Unlock();
}
else
{
// Any other value indicates either: 1) that this is a reader releasing
// the lock and there are other active readers, or 2) that this is the
// last reader releasing the lock and there are no waiting writers.
//
SYNC_CHECK_ASSERT(prevCount > 0);
}
}
// Set new state to what it would be when the lock is acquired for write access
// by a writer from the waiting list.
// Return FALSE if write access can not be acquired in the current state.
//
bool ProposeWriteAfterWaitState()
{
SYNC_CHECK_ASSERT(_current.WaitingWriters() != 0);
if (_current.ActiveReaders() != 0)
return false;
_next.ActiveReaders() = WRITE_LOCKVAL;
_next.WaitingWriters() = _current.WaitingWriters() - 1;
return true;
}
// Set new state to what it would be when the lock is released.
//
void ProposeUnlockState()
{
if (_current.ActiveReaders() == WRITE_LOCKVAL)
{
_next.ActiveReaders() = 0; //Release write lock
}
else
{
SYNC_CHECK_ASSERT(_current.ActiveReaders() != 0);
_next.ActiveReaders() = _current.ActiveReaders() - 1; // Release read lock
}
_next.WaitingWriters() = _current.WaitingWriters();
}
// Set new state to what it would be when one more writer is added to the waiting
// list of the current state.
//
void ProposeWaitState()
{
_next.ActiveReaders() = _current.ActiveReaders();
_next.WaitingWriters() = _current.WaitingWriters() + 1;
SYNC_CHECK_ASSERT(_next.WaitingWriters() != 0);
}
