Refactor thread management for incoming packets.

Build/MQTTnet.nuspec

@@ -15,7 +15,7 @@
 * [Core] Added several packet validations.
 * [Core] Log messages now contain the complete source path including parent components.
 * [Core] The adapter now has an _Endpoint_ definition as string containing remote IP and port.
-* [Client] Received messages are now processed in the worker thread by default. Added a new setting for switching back to dedicated threads.
+* [Client] Received messages are now processed completely in the worker thread without creating new Tasks.
 * [Client] Fixed wrong calculation for sending keep alive packets (thanks to @cstichlberger)
 * [ManagedClient] Fixed a loading issue of stored application messages (thanks to @JTrotta).
 * [Server] Added support for other WebSocket sub protocol formats like mqttv-3.1.1 (thanks to @israellot).

Frameworks/MQTTnet.NetStandard/Adapter/MqttChannelAdapter.cs

@@ -135,9 +135,10 @@ namespace MQTTnet.Adapter
         {
             var fixedHeader = await MqttPacketReader.ReadFixedHeaderAsync(channel, cancellationToken).ConfigureAwait(false);
             
-            ReadingPacketStarted?.Invoke(this, EventArgs.Empty);
             try
             {
+                ReadingPacketStarted?.Invoke(this, EventArgs.Empty);
+
                 var bodyLength = await MqttPacketReader.ReadBodyLengthAsync(channel, cancellationToken).ConfigureAwait(false);
                 if (bodyLength == 0)
                 {

Frameworks/MQTTnet.NetStandard/Client/IMqttClientOptions.cs

@@ -14,8 +14,7 @@ namespace MQTTnet.Client
         TimeSpan CommunicationTimeout { get; }
         TimeSpan KeepAlivePeriod { get; }
         TimeSpan? KeepAliveSendInterval { get; }
-        MqttReceivedApplicationMessageProcessingMode ReceivedApplicationMessageProcessingMode { get; }
-
+        
         MqttApplicationMessage WillMessage { get; }
     }
 }

Frameworks/MQTTnet.NetStandard/Client/MqttClient.cs

@@ -19,7 +19,7 @@ namespace MQTTnet.Client
         private readonly Stopwatch _sendTracker = new Stopwatch();
         private readonly SemaphoreSlim _disconnectLock = new SemaphoreSlim(1, 1);
         private readonly MqttPacketDispatcher _packetDispatcher = new MqttPacketDispatcher();
-
+        
         private readonly IMqttClientAdapterFactory _adapterFactory;
         private readonly IMqttNetChildLogger _logger;
 
@@ -390,25 +390,7 @@ namespace MQTTnet.Client
                 while (!cancellationToken.IsCancellationRequested)
                 {
                     var packet = await _adapter.ReceivePacketAsync(TimeSpan.Zero, cancellationToken).ConfigureAwait(false);
-
-                    if (cancellationToken.IsCancellationRequested)
-                    {
-                        return;
-                    }
-
-                    if (packet == null)
-                    {
-                        continue;
-                    }
-
-                    if (_options.ReceivedApplicationMessageProcessingMode == MqttReceivedApplicationMessageProcessingMode.SingleThread)
-                    {
-                        await ProcessReceivedPacketAsync(packet, cancellationToken).ConfigureAwait(false);
-                    }
-                    else if (_options.ReceivedApplicationMessageProcessingMode == MqttReceivedApplicationMessageProcessingMode.DedicatedThread)
-                    {
-                        StartProcessReceivedPacketAsync(packet, cancellationToken);
-                    }
+                    await ProcessReceivedPacketAsync(packet, cancellationToken).ConfigureAwait(false);
                 }
             }
             catch (Exception exception)
@@ -434,40 +416,30 @@ namespace MQTTnet.Client
             }
         }
 
-        private async Task ProcessReceivedPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
+        private Task ProcessReceivedPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
         {
-            try
+            if (packet is MqttPublishPacket publishPacket)
             {
-                if (packet is MqttPublishPacket publishPacket)
-                {
-                    await ProcessReceivedPublishPacketAsync(publishPacket, cancellationToken).ConfigureAwait(false);
-                    return;
-                }
-
-                if (packet is MqttPingReqPacket)
-                {
-                    await SendAsync(new MqttPingRespPacket(), cancellationToken).ConfigureAwait(false);
-                    return;
-                }
-
-                if (packet is MqttDisconnectPacket)
-                {
-                    await DisconnectAsync().ConfigureAwait(false);
-                    return;
-                }
-
-                if (packet is MqttPubRelPacket pubRelPacket)
-                {
-                    await ProcessReceivedPubRelPacket(pubRelPacket, cancellationToken).ConfigureAwait(false);
-                    return;
-                }
-
-                _packetDispatcher.Dispatch(packet);
+                return ProcessReceivedPublishPacketAsync(publishPacket, cancellationToken);
             }
-            catch (Exception exception)
+
+            if (packet is MqttPingReqPacket)
             {
-                _logger.Error(exception, "Unhandled exception while processing received packet.");
+                return SendAsync(new MqttPingRespPacket(), cancellationToken);
             }
+
+            if (packet is MqttDisconnectPacket)
+            {
+                return DisconnectAsync();
+            }
+
+            if (packet is MqttPubRelPacket pubRelPacket)
+            {
+                return ProcessReceivedPubRelPacket(pubRelPacket, cancellationToken);
+            }
+
+            _packetDispatcher.Dispatch(packet);
+            return Task.FromResult(0);
         }
 
         private Task ProcessReceivedPublishPacketAsync(MqttPublishPacket publishPacket, CancellationToken cancellationToken)
@@ -518,13 +490,6 @@ namespace MQTTnet.Client
                 cancellationToken);
         }
 
-        private void StartProcessReceivedPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
-        {
-#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
-            Task.Run(() => ProcessReceivedPacketAsync(packet, cancellationToken), cancellationToken);
-#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
-        }
-
         private void FireApplicationMessageReceivedEvent(MqttPublishPacket publishPacket)
         {
             try

Frameworks/MQTTnet.NetStandard/Client/MqttClientOptions.cs

@@ -14,8 +14,7 @@ namespace MQTTnet.Client
         public TimeSpan CommunicationTimeout { get; set; } = TimeSpan.FromSeconds(10);
         public TimeSpan KeepAlivePeriod { get; set; } = TimeSpan.FromSeconds(15);
         public TimeSpan? KeepAliveSendInterval { get; set; }
-        public MqttReceivedApplicationMessageProcessingMode ReceivedApplicationMessageProcessingMode { get; set; } = MqttReceivedApplicationMessageProcessingMode.SingleThread;
-
+        
         public MqttApplicationMessage WillMessage { get; set; }
     }
 }

Frameworks/MQTTnet.NetStandard/Client/MqttClientOptionsBuilder.cs

@@ -114,13 +114,6 @@ namespace MQTTnet.Client
             return this;
         }
 
-        public MqttClientOptionsBuilder WithReceivedApplicationMessageProcessingMode(
-            MqttReceivedApplicationMessageProcessingMode mode)
-        {
-            _options.ReceivedApplicationMessageProcessingMode = mode;
-            return this;
-        }
-
         public IMqttClientOptions Build()
         {
             if (_tlsOptions != null)

Frameworks/MQTTnet.NetStandard/Client/MqttPacketDispatcher.cs

@@ -13,7 +13,7 @@ namespace MQTTnet.Client
         {
             foreach (var awaiter in _awaiters)
             {
-                awaiter.Value.SetException(exception);
+                Task.Run(() => awaiter.Value.SetException(exception)); // Task.Run fixes a dead lock. Without this the client only receives one message.
             }
         }
 
@@ -30,9 +30,10 @@ namespace MQTTnet.Client
             var type = packet.GetType();
             var key = new Tuple<ushort, Type>(identifier, type);
             
-            if (_awaiters.TryRemove(key, out var tcs))
+            if (_awaiters.TryRemove(key, out var awaiter))
             {
-                tcs.TrySetResult(packet);
+                awaiter.SetResult(packet);
+                Task.Run(() => awaiter.SetResult(packet)); // Task.Run fixes a dead lock. Without this the client only receives one message.
                 return;
             }
 
@@ -70,7 +71,7 @@ namespace MQTTnet.Client
             }
 
             var key = new Tuple<ushort, Type>(identifier ?? 0, typeof(TResponsePacket));
-            _awaiters.TryRemove(key, out var _);
+            _awaiters.TryRemove(key, out _);
         }
     }
 }

Frameworks/MQTTnet.NetStandard/Client/MqttReceivedApplicationMessageProcessingMode.cs

@@ -1,8 +0,0 @@
-namespace MQTTnet.Client
-{
-    public enum MqttReceivedApplicationMessageProcessingMode
-    {
-        SingleThread,
-        DedicatedThread
-    }
-}