Fix freezes in _AsyncLock_ (#1549)

Source/MQTTnet/Server/Events/ValidatingConnectionEventArgs.cs

@@ -10,6 +10,7 @@ using System.Text;
 using MQTTnet.Adapter;
 using MQTTnet.Formatter;
 using MQTTnet.Implementations;
+using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
 
@@ -88,7 +89,7 @@ namespace MQTTnet.Server
         /// </summary>
         public uint MaximumPacketSize => _connectPacket.MaximumPacketSize;
 
-        public string Password => Encoding.UTF8.GetString(RawPassword ?? PlatformAbstractionLayer.EmptyByteArray);
+        public string Password => Encoding.UTF8.GetString(RawPassword ?? EmptyBuffer.Array);
 
         public MqttProtocolVersion ProtocolVersion => ChannelAdapter.PacketFormatterAdapter.ProtocolVersion;
 

Source/MQTTnet/Server/Internal/MqttClient.cs

@@ -181,7 +181,7 @@ namespace MQTTnet.Server
                 return _eventContainer.ClientAcknowledgedPublishPacketEvent.TryInvokeAsync(eventArgs, _logger);
             }
 
-            return PlatformAbstractionLayer.CompletedTask;
+            return CompletedTask.Instance;
         }
 
         Task HandleIncomingPubAckPacket(MqttPubAckPacket pubAckPacket)
@@ -193,7 +193,7 @@ namespace MQTTnet.Server
                 return ClientAcknowledgedPublishPacket(acknowledgedPublishPacket, pubAckPacket);
             }
 
-            return PlatformAbstractionLayer.CompletedTask;
+            return CompletedTask.Instance;
         }
 
         Task HandleIncomingPubCompPacket(MqttPubCompPacket pubCompPacket)
@@ -205,7 +205,7 @@ namespace MQTTnet.Server
                 return ClientAcknowledgedPublishPacket(acknowledgedPublishPacket, pubCompPacket);
             }
 
-            return PlatformAbstractionLayer.CompletedTask;
+            return CompletedTask.Instance;
         }
 
         async Task HandleIncomingPublishPacket(MqttPublishPacket publishPacket, CancellationToken cancellationToken)

Source/MQTTnet/Server/Internal/MqttClientSessionsManager.cs

@@ -306,6 +306,9 @@ namespace MQTTnet.Server
 
                 await client.RunAsync().ConfigureAwait(false);
             }
+            catch (ObjectDisposedException)
+            {
+            }
             catch (OperationCanceledException)
             {
             }
@@ -479,7 +482,7 @@ namespace MQTTnet.Server
                 sessionShouldPersist = !connectPacket.CleanSession;
             }
 
-            using (await _createConnectionSyncRoot.WaitAsync(CancellationToken.None).ConfigureAwait(false))
+            using (await _createConnectionSyncRoot.EnterAsync().ConfigureAwait(false))
             {
                 MqttSession session;
                 lock (_sessionsManagementLock)
@@ -537,6 +540,7 @@ namespace MQTTnet.Server
                             MqttClientDisconnectType.Takeover,
                             existingClient.Endpoint,
                             existingClient.Session.Items);
+                        
                         await _eventContainer.ClientDisconnectedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
                     }
                 }

Source/MQTTnet/Server/Internal/MqttRetainedMessagesManager.cs

@@ -5,10 +5,8 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Diagnostics;
-using MQTTnet.Implementations;
 using MQTTnet.Internal;
 
 namespace MQTTnet.Server
@@ -85,7 +83,7 @@ namespace MQTTnet.Server
                         }
                         else
                         {
-                            if (existingMessage.QualityOfServiceLevel != applicationMessage.QualityOfServiceLevel || !existingMessage.Payload.SequenceEqual(applicationMessage.Payload ?? PlatformAbstractionLayer.EmptyByteArray))
+                            if (existingMessage.QualityOfServiceLevel != applicationMessage.QualityOfServiceLevel || !existingMessage.Payload.SequenceEqual(applicationMessage.Payload ?? EmptyBuffer.Array))
                             {
                                 _messages[applicationMessage.Topic] = applicationMessage;
                                 saveIsRequired = true;
@@ -103,7 +101,7 @@ namespace MQTTnet.Server
 
                 if (saveIsRequired)
                 {
-                    using (await _storageAccessLock.WaitAsync(CancellationToken.None).ConfigureAwait(false))
+                    using (await _storageAccessLock.EnterAsync().ConfigureAwait(false))
                     {
                         var eventArgs = new RetainedMessageChangedEventArgs(clientId, applicationMessage, messagesForSave);
                         await _eventContainer.RetainedMessageChangedEvent.InvokeAsync(eventArgs).ConfigureAwait(false);
@@ -132,7 +130,7 @@ namespace MQTTnet.Server
                 _messages.Clear();
             }
 
-            using (await _storageAccessLock.WaitAsync(CancellationToken.None).ConfigureAwait(false))
+            using (await _storageAccessLock.EnterAsync().ConfigureAwait(false))
             {
                 await _eventContainer.RetainedMessagesClearedEvent.InvokeAsync(EventArgs.Empty).ConfigureAwait(false);
             }

Source/MQTTnet/Server/Internal/MqttServerKeepAliveMonitor.cs

@@ -6,7 +6,6 @@ using System;
 using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Diagnostics;
-using MQTTnet.Implementations;
 using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
@@ -14,16 +13,20 @@ namespace MQTTnet.Server
 {
     public sealed class MqttServerKeepAliveMonitor
     {
+        readonly MqttNetSourceLogger _logger;
         readonly MqttServerOptions _options;
         readonly MqttClientSessionsManager _sessionsManager;
-        readonly MqttNetSourceLogger _logger;
 
         public MqttServerKeepAliveMonitor(MqttServerOptions options, MqttClientSessionsManager sessionsManager, IMqttNetLogger logger)
         {
             _options = options ?? throw new ArgumentNullException(nameof(options));
             _sessionsManager = sessionsManager ?? throw new ArgumentNullException(nameof(sessionsManager));
-            
-            if (logger == null) throw new ArgumentNullException(nameof(logger));
+
+            if (logger == null)
+            {
+                throw new ArgumentNullException(nameof(logger));
+            }
+
             _logger = logger.WithSource(nameof(MqttServerKeepAliveMonitor));
         }
 
@@ -45,7 +48,7 @@ namespace MQTTnet.Server
                 while (!cancellationToken.IsCancellationRequested)
                 {
                     TryProcessClients();
-                    PlatformAbstractionLayer.Sleep(_options.KeepAliveMonitorInterval);
+                    Sleep(_options.KeepAliveMonitorInterval);
                 }
             }
             catch (OperationCanceledException)
@@ -61,13 +64,22 @@ namespace MQTTnet.Server
             }
         }
 
-        void TryProcessClients()
+        static void Sleep(TimeSpan timeout)
         {
-            var now = DateTime.UtcNow;
-            foreach (var client in _sessionsManager.GetClients())
+#if !NETSTANDARD1_3 && !WINDOWS_UWP
+            try
             {
-                TryProcessClient(client, now);
+                Thread.Sleep(timeout);
             }
+            catch (ThreadAbortException)
+            {
+                // The ThreadAbortException is not actively catched in this project.
+                // So we use a one which is similar and will be catched properly.
+                throw new OperationCanceledException();
+            }
+#else
+            Task.Delay(timeout).Wait();
+#endif
         }
 
         void TryProcessClient(MqttClient connection, DateTime now)
@@ -119,5 +131,14 @@ namespace MQTTnet.Server
                 _logger.Error(exception, "Client {0}: Unhandled exception while checking keep alive timeouts.", connection.Id);
             }
         }
+
+        void TryProcessClients()
+        {
+            var now = DateTime.UtcNow;
+            foreach (var client in _sessionsManager.GetClients())
+            {
+                TryProcessClient(client, now);
+            }
+        }
     }
-}
+}

Source/MQTTnet/Server/MqttServer.cs

@@ -11,7 +11,6 @@ using System.Threading;
 using System.Threading.Tasks;
 using MQTTnet.Adapter;
 using MQTTnet.Diagnostics;
-using MQTTnet.Implementations;
 using MQTTnet.Internal;
 using MQTTnet.Packets;
 using MQTTnet.Protocol;
@@ -172,7 +171,7 @@ namespace MQTTnet.Server
         {
             ThrowIfNotStarted();
 
-            return _retainedMessagesManager?.ClearMessages() ?? PlatformAbstractionLayer.CompletedTask;
+            return _retainedMessagesManager?.ClearMessages() ?? CompletedTask.Instance;
         }
 
         public Task DisconnectClientAsync(string id, MqttDisconnectReasonCode reasonCode)

Source/MQTTnet/Server/Status/MqttSessionStatus.cs

@@ -6,7 +6,6 @@ using System;
 using System.Collections;
 using System.Threading.Tasks;
 using MQTTnet.Formatter;
-using MQTTnet.Implementations;
 using MQTTnet.Internal;
 
 namespace MQTTnet.Server
@@ -34,8 +33,8 @@ namespace MQTTnet.Server
             
             var publishPacketFactory = new MqttPublishPacketFactory();
             _session.EnqueueDataPacket(new MqttPacketBusItem(publishPacketFactory.Create(applicationMessage)));
-            
-            return PlatformAbstractionLayer.CompletedTask;
+
+            return CompletedTask.Instance;
         }
 
         public Task DeliverApplicationMessageAsync(MqttApplicationMessage applicationMessage)