private void ActivateNextQueueItemWithValidatedToken(int token)
{
// see if we can nudge the next waiter
lock (_queue)
{
if (Volatile.Read(ref _token) != token)
{
Throw.InvalidLockHolder();
}
try
{
if (_queue.Count == 0)
{
Log($"no pending items to activate");
return;
}
// there's work to do; get a new token
Log($"pending items: {_queue.Count}");
// we're expecting to activate; get a new token speculatively
// (needs to be new so the old caller can't double-dispose and
// release someone else's lock)
Volatile.Write(ref _token, token = LockState.GetNextToken(token));
// try to give the new token to someone
while (_queue.Count != 0)
{
var next = DequeueInsideLock();
if (next.TrySetResult(token))
{
Log($"handed lock to {next}");
token = 0; // so we don't release the token
return;
}
else
{
Log($"lock rejected by {next}");
}
}
}
finally
{
if (token != 0) // nobody actually wanted it; return it
{ // (this could be the original token, or a new speculative token)
Log("returning unwanted lock");
Volatile.Write(ref _token, LockState.ChangeState(token, LockState.Pending));
}
SetNextAsyncTimeoutInsideLock();
}
}
}