Execute disconnected handler in new task.

Source/MQTTnet/Client/MqttClient.cs

@@ -13,6 +13,7 @@ using MQTTnet.Client.Subscribing;
 using MQTTnet.Client.Unsubscribing;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
+using MQTTnet.Internal;
 using MQTTnet.PacketDispatcher;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
@@ -287,7 +288,9 @@ namespace MQTTnet.Client
                 var disconnectedHandler = DisconnectedHandler;
                 if (disconnectedHandler != null)
                 {
-                    await disconnectedHandler.HandleDisconnectedAsync(new MqttClientDisconnectedEventArgs(clientWasConnected, exception, authenticateResult)).ConfigureAwait(false);
+                    // This handler must be executed in a new thread because otherwise a dead lock may happen
+                    // when trying to reconnect in that handler etc.
+                    Task.Run(() => disconnectedHandler.HandleDisconnectedAsync(new MqttClientDisconnectedEventArgs(clientWasConnected, exception, authenticateResult))).Forget(_logger);
                 }
             }
         }
@@ -648,4 +651,4 @@ namespace MQTTnet.Client
             return Interlocked.CompareExchange(ref _disconnectGate, 1, 0) != 0;
         }
     }
-}
+}

Source/MQTTnet/Internal/TaskExtensions.cs

@@ -0,0 +1,17 @@
+using System.Threading.Tasks;
+using MQTTnet.Diagnostics;
+
+namespace MQTTnet.Internal
+{
+    public static class TaskExtensions
+    {
+        public static void Forget(this Task task, IMqttNetChildLogger logger)
+        {
+            task?.ContinueWith(t =>
+                {
+                    logger.Error(t.Exception, "Unhandled exception.");
+                },
+                TaskContinuationOptions.OnlyOnFaulted);
+        }
+    }
+}