private bool TryOffset(int releaseCount, out int previous, SemaphoreSlimState state)
{
var expected = Volatile.Read(ref _count);
previous = expected;
if (_maxCount.HasValue && expected + (long)releaseCount > (long)_maxCount)
{
throw new SemaphoreFullException();
}
var result = expected + releaseCount;
if (result < 0)
{
return(false);
}
var found = Interlocked.CompareExchange(ref _count, result, expected);
if (found != expected)
{
return(false);
}
SyncWaitHandle(state);
return(true);
}
private void Awake(SemaphoreSlimState state)
{
var spinWait = new SpinWait();
while (state.AsyncWaiters.TryTake(out var waiter))
{
if (waiter.Task.IsCompleted)
{
// Skip - either canceled or timed out
continue;
}
if (TryOffset(-1, out _, state))
{
waiter.SetResult(true);
}
else
{
// Add it back
state.AsyncWaiters.Add(waiter);
break;
}
spinWait.SpinOnce();
}
}
private void SyncWaitHandle(SemaphoreSlimState state)
{
var awake = false;
if (Volatile.Read(ref _count) == 0 == state.CanEnter.IsSet && Interlocked.CompareExchange(ref _syncRoot, 1, 0) == 0)
{
try
{
awake = SyncWaitHandleExtracted();
}
finally
{
Volatile.Write(ref _syncRoot, 0);
}
}
if (awake)
{
ThreadPool.QueueUserWorkItem(_ => Awake(state));
}
bool SyncWaitHandleExtracted()
{
int found;
var canEnter = state.CanEnter;
if ((found = Volatile.Read(ref _count)) == 0 != canEnter.IsSet)
{
return(false);
}
if (found == 0)
{
canEnter.Reset();
}
else
{
canEnter.Set();
return(true);
}
return(false);
}
}