System.Net.WebSockets.ManagedWebSocket.SendFrameFallbackAsync C# (CSharp) Method

        private async Task SendFrameFallbackAsync(MessageOpcode opcode, bool endOfMessage, ArraySegment<byte> payloadBuffer, CancellationToken cancellationToken)
        {
            await _sendFrameAsyncLock.WaitAsync().ConfigureAwait(false);
            try
            {
                int sendBytes = WriteFrameToSendBuffer(opcode, endOfMessage, payloadBuffer);
                using (cancellationToken.Register(s => ((ManagedWebSocket)s).Abort(), this))
                {
                    await _stream.WriteAsync(_sendBuffer, 0, sendBytes, cancellationToken).ConfigureAwait(false);
                }
            }
            catch (Exception exc)
            {
                throw _state == WebSocketState.Aborted ?
                    CreateOperationCanceledException(exc, cancellationToken) :
                    new WebSocketException(WebSocketError.ConnectionClosedPrematurely, exc);
            }
            finally
            {
                _sendFrameAsyncLock.Release();
            }
        }