Refactor code.

Build/MQTTnet.nuspec

@@ -18,6 +18,7 @@
 * [Client] Improved keep alive message sending.
 * [Client] Added support for deferred message approval (#1075, thanks to @tkurucsai).
 * [Client] Exposed missing APIs for .NET 5.0 build (thanks to @yyjdelete).
+* [Client] Improved disconnect handling (#1134, thanks to @yyjdelete).
 * [RpcClient] Fixed an issue when using a custom application message reveived handler (#1093).
 * [RpcClient] Fixed a race condition when using timeout and cancellation token at the same time (BREAKING CHANGE!).
 * [Server] Improved keep alive message sending.

Source/MQTTnet/Client/MqttClient.cs

@@ -320,10 +320,12 @@ namespace MQTTnet.Client
         Task DisconnectInternalAsync(Task sender, Exception exception, MqttClientAuthenticateResult authenticateResult)
         {
             var clientWasConnected = IsConnected;
+            
             if (!DisconnectIsPendingOrFinished())
             {
                 return DisconnectCoreAsync(sender, exception, authenticateResult, clientWasConnected);
             }
+            
             return PlatformAbstractionLayer.CompletedTask;
         }
 
@@ -371,8 +373,7 @@ namespace MQTTnet.Client
                 {
                     // 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, _disconnectReason)))
+                    Task.Run(() => disconnectedHandler.HandleDisconnectedAsync(new MqttClientDisconnectedEventArgs(clientWasConnected, exception, authenticateResult, _disconnectReason))).RunInBackground(_logger);
-                        .RunInBackground(_logger);
                 }
             }
         }
@@ -798,6 +799,7 @@ namespace MQTTnet.Client
         bool DisconnectIsPendingOrFinished()
         {
             var connectionStatus = (MqttClientConnectionStatus)_connectionStatus;
+            
             do
             {
                 switch (connectionStatus)
@@ -814,6 +816,7 @@ namespace MQTTnet.Client
                         {
                             return false;
                         }
+                        
                         connectionStatus = curStatus;
                         break;
                 }

Source/MQTTnet/Client/MqttClientConnectionStatus.cs

@@ -1,9 +1,8 @@
 namespace MQTTnet.Client
 {
     public enum MqttClientConnectionStatus
-
     {
-        Disconnected = 0,
+        Disconnected,
         Disconnecting,
         Connected,
         Connecting