Remove lock to prevent dead locks

MQTTnet.Core/Adapter/MqttChannelCommunicationAdapter.cs

@@ -17,7 +17,7 @@ namespace MQTTnet.Core.Adapter
     {
         private readonly IMqttCommunicationChannel _channel;
 
-        private Task _sendTask = Task.FromResult(0); // this task is used to prevent overlapping write
+        private readonly Task _waitTask = Task.FromResult(0); // this task is used to prevent overlapping write
 
         public MqttChannelCommunicationAdapter(IMqttCommunicationChannel channel, IMqttPacketSerializer serializer)
         {
@@ -79,31 +79,30 @@ namespace MQTTnet.Core.Adapter
         {
             try
             {
-                lock (_channel)
+                var waitTask = _waitTask;
+
+                foreach (var packet in packets)
                 {
-                    foreach (var packet in packets)
-                    {
-                        if (packet == null) {continue; }
+                    if (packet == null) { continue; }
 
-                        MqttTrace.Information(nameof(MqttChannelCommunicationAdapter), $"TX >>> {packet} [Timeout={timeout}]");
+                    MqttTrace.Information(nameof(MqttChannelCommunicationAdapter), $"TX >>> {packet} [Timeout={timeout}]");
 
-                        var writeBuffer = PacketSerializer.Serialize(packet);
-                        _sendTask = _sendTask.ContinueWith(p => _channel.SendStream.WriteAsync(writeBuffer, 0, writeBuffer.Length, cancellationToken).ConfigureAwait(false), cancellationToken);
-                    }
+                    var writeBuffer = PacketSerializer.Serialize(packet);
+
+                    waitTask = waitTask.ContinueWith(t => _channel.SendStream.WriteAsync(writeBuffer, 0, writeBuffer.Length, cancellationToken).ConfigureAwait(false), cancellationToken);
+                }
 
+                waitTask = waitTask.ContinueWith(t =>
+                {
                     if (timeout > TimeSpan.Zero)
                     {
-                        _sendTask = _sendTask.ContinueWith(c => _channel.SendStream.FlushAsync(cancellationToken).TimeoutAfter(timeout), cancellationToken).ConfigureAwait(false);
-                    }
-                    else
-                    {
-                        _sendTask = _sendTask.ContinueWith(c => _channel.SendStream.FlushAsync(cancellationToken), cancellationToken);
+                        return _channel.SendStream.FlushAsync(cancellationToken).TimeoutAfter(timeout).ConfigureAwait(false);
                     }
 
-                }
-
-                await _sendTask; // configure await false generates stackoverflow
+                    return _channel.SendStream.FlushAsync(cancellationToken).ConfigureAwait(false);
+                }, cancellationToken);
 
+                await waitTask; // configure await false generates stackoverflow
             }
             catch (TaskCanceledException)
             {