/// <summary>
/// Private helper to actually perform the Set.
/// </summary>
/// <param name="duringCancellation">Indicates whether we are calling Set() during cancellation.</param>
/// <exception cref="T:System.OperationCanceledException">The object has been canceled.</exception>
private void Set(bool duringCancellation)
{
// We need to ensure that IsSet=true does not get reordered past the read of m_eventObj
// This would be a legal movement according to the .NET memory model.
// The code is safe as IsSet involves an Interlocked.CompareExchange which provides a full memory barrier.
IsSet = true;
// If there are waiting threads, we need to pulse them.
if (Waiters > 0)
{
Debug.Assert(m_lock != null && m_condition != null); //if waiters>0, then m_lock has already been created.
using (LockHolder.Hold(m_lock))
{
m_condition.SignalAll();
}
}
ManualResetEvent eventObj = m_eventObj;
//Design-decision: do not set the event if we are in cancellation -> better to deadlock than to wake up waiters incorrectly
//It would be preferable to wake up the event and have it throw OCE. This requires MRE to implement cancellation logic
if (eventObj != null && !duringCancellation)
{
// We must surround this call to Set in a lock. The reason is fairly subtle.
// Sometimes a thread will issue a Wait and wake up after we have set m_state,
// but before we have gotten around to setting m_eventObj (just below). That's
// because Wait first checks m_state and will only access the event if absolutely
// necessary. However, the coding pattern { event.Wait(); event.Dispose() } is
// quite common, and we must support it. If the waiter woke up and disposed of
// the event object before the setter has finished, however, we would try to set a
// now-disposed Win32 event. Crash! To deal with this race, we use a lock to
// protect access to the event object when setting and disposing of it. We also
// double-check that the event has not become null in the meantime when in the lock.
lock (eventObj)
{
if (m_eventObj != null)
{
// If somebody is waiting, we must set the event.
m_eventObj.Set();
}
}
}
#if DEBUG
m_lastSetTime = Environment.TickCount;
#endif
}
/// <summary>
/// Exits the <see cref="SemaphoreSlim"/> a specified number of times.
/// </summary>
/// <param name="releaseCount">The number of times to exit the semaphore.</param>
/// <returns>The previous count of the <see cref="SemaphoreSlim"/>.</returns>
/// <exception cref="T:System.ArgumentOutOfRangeException"><paramref name="releaseCount"/> is less
/// than 1.</exception>
/// <exception cref="T:System.Threading.SemaphoreFullException">The <see cref="SemaphoreSlim"/> has
/// already reached its maximum size.</exception>
/// <exception cref="T:System.ObjectDisposedException">The current instance has already been
/// disposed.</exception>
public int Release(int releaseCount)
{
CheckDispose();
// Validate input
if (releaseCount < 1)
{
throw new ArgumentOutOfRangeException(
"releaseCount", releaseCount, SR.SemaphoreSlim_Release_CountWrong);
}
int returnCount;
using (LockHolder.Hold(m_lock))
{
// Read the m_currentCount into a local variable to avoid unnecessary volatile accesses inside the lock.
int currentCount = m_currentCount;
returnCount = currentCount;
// If the release count would result exceeding the maximum count, throw SemaphoreFullException.
if (m_maxCount - currentCount < releaseCount)
{
throw new SemaphoreFullException();
}
// Increment the count by the actual release count
currentCount += releaseCount;
// Signal to any synchronous waiters
int waitCount = m_waitCount;
if (currentCount == 1 || waitCount == 1)
{
m_condition.SignalOne();
}
else if (waitCount > 1)
{
m_condition.SignalAll();
}
// Now signal to any asynchronous waiters, if there are any. While we've already
// signaled the synchronous waiters, we still hold the lock, and thus
// they won't have had an opportunity to acquire this yet. So, when releasing
// asynchronous waiters, we assume that all synchronous waiters will eventually
// acquire the semaphore. That could be a faulty assumption if those synchronous
// waits are canceled, but the wait code path will handle that.
if (m_asyncHead != null)
{
Debug.Assert(m_asyncTail != null, "tail should not be null if head isn't null");
int maxAsyncToRelease = currentCount - waitCount;
while (maxAsyncToRelease > 0 && m_asyncHead != null)
{
--currentCount;
--maxAsyncToRelease;
// Get the next async waiter to release and queue it to be completed
var waiterTask = m_asyncHead;
RemoveAsyncWaiter(waiterTask); // ensures waiterTask.Next/Prev are null
QueueWaiterTask(waiterTask);
}
}
m_currentCount = currentCount;
// Exposing wait handle if it is not null
if (m_waitHandle != null && returnCount == 0 && currentCount > 0)
{
m_waitHandle.Set();
}
}
// And return the count
return(returnCount);
}
