internal HttpListenerAsyncResult BeginGetContext(HttpListenerAsyncResult asyncResult) { CheckDisposed (); if (_prefixes.Count == 0) throw new InvalidOperationException ("The listener has no URI prefix on which listens."); if (!_listening) throw new InvalidOperationException ("The listener hasn't been started."); // Lock _waitQueue early to avoid race conditions. lock (_waitQueueSync) { lock (_ctxQueueSync) { var ctx = getContextFromQueue (); if (ctx != null) { asyncResult.Complete (ctx, true); return asyncResult; } } _waitQueue.Add (asyncResult); } return asyncResult; }