Refactor serializer locking and thread instances.

Build/MQTTnet.AspNetCore.nuspec

@@ -13,11 +13,9 @@
     <releaseNotes>* Updated to MQTTnet 2.8.0.
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
-    <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 
+    <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags>
     <dependencies>
-      <group targetFramework="netstandard2.0">
+      <dependency id="MQTTnet" version="2.8.0-alpha5" />
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
     </dependencies>
   </metadata>
 

Build/MQTTnet.Extensions.ManagedClient.nuspec

@@ -15,24 +15,7 @@
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 
     <dependencies>
-      <group targetFramework="netstandard2.0">
+      <dependency id="MQTTnet" version="2.8.0-beta1" />
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="netstandard1.3">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="netstandard2.0">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="uap10.0">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="net452">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="net461">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
     </dependencies>
   </metadata>
 

Build/MQTTnet.Extensions.Rpc.nuspec

@@ -15,24 +15,7 @@
     <copyright>Copyright Christian Kratky 2016-2018</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 
     <dependencies>
-      <group targetFramework="netstandard2.0">
+      <dependency id="MQTTnet" version="2.8.0-beta1" />
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="netstandard1.3">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="netstandard2.0">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="uap10.0">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="net452">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
-      <group targetFramework="net461">
-        <dependency id="MQTTnet" version="2.8.0-alpha5" />
-      </group>
     </dependencies>
   </metadata>
 

Build/MQTTnet.nuspec

@@ -48,7 +48,7 @@
         <dependency id="System.Net.WebSockets.Client" version="4.3.2" />
       </group>
       <group targetFramework="uap10.0">
-        <dependency id="Microsoft.NETCore.UniversalWindowsPlatform" version="5.4.1" />
+        <dependency id="Microsoft.NETCore.UniversalWindowsPlatform" version="6.1.4" />
       </group>
       <group targetFramework="net452">
       </group>

Build/build.ps1

@@ -36,8 +36,8 @@ if ($path) {
 	Remove-Item .\NuGet -Force -Recurse -ErrorAction SilentlyContinue
 
     New-Item -ItemType Directory -Force -Path .\NuGet
-    .\NuGet.exe pack MQTTnet.nuspec -Verbosity detailed -Symbols -OutputDir "NuGet" -Version $nugetVersion
+    .\nuget.exe pack MQTTnet.nuspec -Verbosity detailed -Symbols -OutputDir "NuGet" -Version $nugetVersion
-    .\NuGet.exe pack MQTTnet.AspNetCore.nuspec -Verbosity detailed -Symbols -OutputDir "NuGet" -Version $nugetVersion
+    .\nuget.exe pack MQTTnet.AspNetCore.nuspec -Verbosity detailed -Symbols -OutputDir "NuGet" -Version $nugetVersion
-	.\NuGet.exe pack MQTTnet.Extensions.Rpc.nuspec -Verbosity detailed -Symbols -OutputDir "NuGet" -Version $nugetVersion
+	.\nuget.exe pack MQTTnet.Extensions.Rpc.nuspec -Verbosity detailed -Symbols -OutputDir "NuGet" -Version $nugetVersion
-	.\NuGet.exe pack MQTTnet.Extensions.ManagedClient.nuspec -Verbosity detailed -Symbols -OutputDir "NuGet" -Version $nugetVersion
+	.\nuget.exe pack MQTTnet.Extensions.ManagedClient.nuspec -Verbosity detailed -Symbols -OutputDir "NuGet" -Version $nugetVersion
 }

Build/upload.ps1

@@ -0,0 +1,9 @@
+param([string]$apiKey)
+
+$files = Get-ChildItem -Path ".\NuGet" -Filter "*.nupkg"
+foreach ($file in $files)
+{
+	Write-Host "Uploading: " $file
+
+	.\nuget.exe push $file.Fullname $apiKey -NoSymbols -Source https://api.nuget.org/v3/index.json
+}

MQTTnet.sln

@@ -20,6 +20,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Build", "Build", "{67C28AC1
 		Build\MQTTnet.Extensions.ManagedClient.nuspec = Build\MQTTnet.Extensions.ManagedClient.nuspec
 		Build\MQTTnet.Extensions.Rpc.nuspec = Build\MQTTnet.Extensions.Rpc.nuspec
 		Build\MQTTnet.nuspec = Build\MQTTnet.nuspec
+		Build\upload.ps1 = Build\upload.ps1
 	EndProjectSection
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{B3F60ECB-45BA-4C66-8903-8BB89CA67998}"
@@ -74,6 +75,7 @@ Global
 		{A7FF0C91-25DE-4BA6-B39E-F54E8DADF1CC}.Release|x86.Build.0 = Release|Any CPU
 		{FF1F72D6-9524-4422-9497-3CC0002216ED}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
 		{FF1F72D6-9524-4422-9497-3CC0002216ED}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{FF1F72D6-9524-4422-9497-3CC0002216ED}.Debug|Any CPU.Deploy.0 = Debug|Any CPU
 		{FF1F72D6-9524-4422-9497-3CC0002216ED}.Debug|ARM.ActiveCfg = Debug|ARM
 		{FF1F72D6-9524-4422-9497-3CC0002216ED}.Debug|ARM.Build.0 = Debug|ARM
 		{FF1F72D6-9524-4422-9497-3CC0002216ED}.Debug|ARM.Deploy.0 = Debug|ARM

Source/MQTTnet.Extensions.ManagedClient/ManagedMqttClient.cs

@@ -7,7 +7,6 @@ using System.Threading.Tasks;
 using MQTTnet.Client;
 using MQTTnet.Diagnostics;
 using MQTTnet.Exceptions;
-using MQTTnet.Internal;
 using MQTTnet.Protocol;
 
 namespace MQTTnet.Extensions.ManagedClient
@@ -15,8 +14,7 @@ namespace MQTTnet.Extensions.ManagedClient
     public class ManagedMqttClient : IManagedMqttClient
     {
         private readonly BlockingCollection<ManagedMqttApplicationMessage> _messageQueue = new BlockingCollection<ManagedMqttApplicationMessage>();
-        private readonly Dictionary<string, MqttQualityOfServiceLevel> _subscriptions = new Dictionary<string, MqttQualityOfServiceLevel>();
+        private readonly ConcurrentDictionary<string, MqttQualityOfServiceLevel> _subscriptions = new ConcurrentDictionary<string, MqttQualityOfServiceLevel>();
-        private readonly AsyncLock _subscriptionsLock = new AsyncLock();
         private readonly List<string> _unsubscriptions = new List<string>();
 
         private readonly IMqttClient _mqttClient;
@@ -118,39 +116,36 @@ namespace MQTTnet.Extensions.ManagedClient
             _messageQueue.Add(applicationMessage);
         }
 
-        public async Task SubscribeAsync(IEnumerable<TopicFilter> topicFilters)
+        public Task SubscribeAsync(IEnumerable<TopicFilter> topicFilters)
         {
             if (topicFilters == null) throw new ArgumentNullException(nameof(topicFilters));
 
-            using (await _subscriptionsLock.LockAsync(CancellationToken.None).ConfigureAwait(false))
+            foreach (var topicFilter in topicFilters)
             {
-                foreach (var topicFilter in topicFilters)
+                _subscriptions[topicFilter.Topic] = topicFilter.QualityOfServiceLevel;
+                _subscriptionsNotPushed = true;
+            }
+
+            return Task.FromResult(0);
+        }
+
+        public Task UnsubscribeAsync(IEnumerable<string> topics)
+        {
+            foreach (var topic in topics)
+            {
+                if (_subscriptions.TryRemove(topic, out _))
                 {
-                    _subscriptions[topicFilter.Topic] = topicFilter.QualityOfServiceLevel;
+                    _unsubscriptions.Add(topic);
                     _subscriptionsNotPushed = true;
                 }
             }
-        }
 
-        public async Task UnsubscribeAsync(IEnumerable<string> topics)
+            return Task.FromResult(0);
-        {
-            using (await _subscriptionsLock.LockAsync(CancellationToken.None).ConfigureAwait(false))
-            {
-                foreach (var topic in topics)
-                {
-                    if (_subscriptions.Remove(topic))
-                    {
-                        _unsubscriptions.Add(topic);
-                        _subscriptionsNotPushed = true;
-                    }
-                }
-            }
         }
 
         public void Dispose()
         {
             _messageQueue?.Dispose();
-            _subscriptionsLock?.Dispose();
             _connectionCancellationToken?.Dispose();
             _publishingCancellationToken?.Dispose();
         }
@@ -289,7 +284,7 @@ namespace MQTTnet.Extensions.ManagedClient
             List<TopicFilter> subscriptions;
             List<string> unsubscriptions;
 
-            using (await _subscriptionsLock.LockAsync(CancellationToken.None).ConfigureAwait(false))
+            lock (_subscriptions)
             {
                 subscriptions = _subscriptions.Select(i => new TopicFilter(i.Key, i.Value)).ToList();
 

Source/MQTTnet/Adapter/MqttChannelAdapter.cs

@@ -18,6 +18,8 @@ namespace MQTTnet.Adapter
         private const uint ErrorOperationAborted = 0x800703E3;
         private const int ReadBufferSize = 4096;  // TODO: Move buffer size to config
 
+        private readonly SemaphoreSlim _writerSemaphore = new SemaphoreSlim(1, 1);
+
         private readonly IMqttNetChildLogger _logger;
         private readonly IMqttChannel _channel;
 
@@ -88,6 +90,7 @@ namespace MQTTnet.Adapter
 
         public async Task SendPacketAsync(MqttBasePacket packet, CancellationToken cancellationToken)
         {
+            await _writerSemaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
             try
             {
                 _logger.Verbose("TX >>> {0}", packet);
@@ -107,6 +110,10 @@ namespace MQTTnet.Adapter
 
                 WrapException(exception);
             }
+            finally
+            {
+                _writerSemaphore.Release();
+            }
         }
 
         public async Task<MqttBasePacket> ReceivePacketAsync(TimeSpan timeout, CancellationToken cancellationToken)

Source/MQTTnet/Diagnostics/MqttNetChildLogger.cs

@@ -9,7 +9,7 @@ namespace MQTTnet.Diagnostics
 
         public MqttNetChildLogger(IMqttNetLogger logger, string source)
         {
-            _logger = logger;
+            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
             _source = source;
         }
 

Source/MQTTnet/Implementations/MqttTcpChannel.Uwp.cs

@@ -40,7 +40,18 @@ namespace MQTTnet.Implementations
 
         public static Func<MqttClientTcpOptions, IEnumerable<ChainValidationResult>> CustomIgnorableServerCertificateErrorsResolver { get; set; }
 
-        public string Endpoint => _socket?.Information?.RemoteAddress?.ToString(); // TODO: Check if contains also the port.
+        public string Endpoint
+        {
+            get
+            {
+                if (_socket?.Information != null)
+                {
+                    return _socket.Information.RemoteAddress + ":" + _socket.Information.RemotePort;
+                }
+
+                return null;
+            }
+        }
 
         public async Task ConnectAsync(CancellationToken cancellationToken)
         {
@@ -81,10 +92,13 @@ namespace MQTTnet.Implementations
             return _readStream.ReadAsync(buffer, offset, count, cancellationToken);
         }
 
-        public async Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        public Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
-            await _writeStream.WriteAsync(buffer, offset, count, cancellationToken);
+            // In the write method only the internal buffer will be filled. So here is no
-            await _writeStream.FlushAsync(cancellationToken);
+            // async/await required. The real network transmit is done when calling the
+            // Flush method.
+            _writeStream.Write(buffer, offset, count);
+            return _writeStream.FlushAsync(cancellationToken);
         }
 
         public void Dispose()

Source/MQTTnet/MQTTnet.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">netstandard1.3;netstandard2.0;net452;uap10.0</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">netstandard1.3;netstandard2.0;net452;net461;uap10.0</TargetFrameworks>
     <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">netstandard1.3;netstandard2.0</TargetFrameworks>
     <AssemblyName>MQTTnet</AssemblyName>
     <RootNamespace>MQTTnet</RootNamespace>
@@ -62,4 +62,7 @@
   <ItemGroup Condition="'$(TargetFramework)'=='net452'">
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFramework)'=='net461'">
+  </ItemGroup>
+
 </Project>

Source/MQTTnet/Serializer/MqttPacketSerializer.cs

@@ -11,8 +11,7 @@ namespace MQTTnet.Serializer
     {
         private const int FixedHeaderSize = 1;
 
-        [ThreadStatic]
+        private readonly MqttPacketWriter _packetWriter = new MqttPacketWriter();
-        private static MqttPacketWriter _packetWriter;
 
         public MqttProtocolVersion ProtocolVersion { get; set; } = MqttProtocolVersion.V311;
 
@@ -20,14 +19,12 @@ namespace MQTTnet.Serializer
         {
             if (packet == null) throw new ArgumentNullException(nameof(packet));
 
-            var packetWriter = InitializePacketWriter();
-
             // Leave enough head space for max header size (fixed + 4 variable remaining length = 5 bytes)
-            packetWriter.Reset();
+            _packetWriter.Reset();
-            packetWriter.Seek(5);
+            _packetWriter.Seek(5);
 
-            var fixedHeader = SerializePacket(packet, packetWriter);
+            var fixedHeader = SerializePacket(packet, _packetWriter);
-            var remainingLength = packetWriter.Length - 5;
+            var remainingLength = _packetWriter.Length - 5;
 
             var remainingLengthBuffer = MqttPacketWriter.EncodeRemainingLength(remainingLength);
 
@@ -35,12 +32,12 @@ namespace MQTTnet.Serializer
             var headerOffset = 5 - headerSize;
 
             // Position cursor on correct offset on beginining of array (has leading 0x0)
-            packetWriter.Seek(headerOffset);
+            _packetWriter.Seek(headerOffset);
-            packetWriter.Write(fixedHeader);
+            _packetWriter.Write(fixedHeader);
-            packetWriter.Write(remainingLengthBuffer.Array, remainingLengthBuffer.Offset, remainingLengthBuffer.Count);
+            _packetWriter.Write(remainingLengthBuffer.Array, remainingLengthBuffer.Offset, remainingLengthBuffer.Count);
 
-            var buffer = packetWriter.GetBuffer();
+            var buffer = _packetWriter.GetBuffer();
-            return new ArraySegment<byte>(buffer, headerOffset, packetWriter.Length - headerOffset);
+            return new ArraySegment<byte>(buffer, headerOffset, _packetWriter.Length - headerOffset);
         }
 
         public MqttBasePacket Deserialize(ReceivedMqttPacket receivedMqttPacket)
@@ -76,7 +73,7 @@ namespace MQTTnet.Serializer
 
         public void FreeBuffer()
         {
-            InitializePacketWriter().FreeBuffer();
+            _packetWriter.FreeBuffer();
         }
 
         private byte SerializePacket(MqttBasePacket packet, MqttPacketWriter packetWriter)
@@ -101,16 +98,6 @@ namespace MQTTnet.Serializer
             }
         }
 
-        private static MqttPacketWriter InitializePacketWriter()
-        {
-            if (_packetWriter == null)
-            {
-                _packetWriter = new MqttPacketWriter();
-            }
-
-            return _packetWriter;
-        }
-
         private static MqttBasePacket DeserializeUnsubAck(MqttPacketBodyReader body)
         {
             ThrowIfBodyIsEmpty(body);

Source/MQTTnet/Serializer/MqttPacketWriter.cs

@@ -12,6 +12,8 @@ namespace MQTTnet.Serializer
     /// </summary>
     public class MqttPacketWriter
     {
+        public static int MaxBufferSize = 4096;
+
         private byte[] _buffer = new byte[128];
 
         private int _position;
@@ -117,12 +119,12 @@ namespace MQTTnet.Serializer
             // a lot and the size will never reduced. So this method tries to find a size which can be held in 
             // memory for a long time without causing troubles.
 
-            if (_buffer.Length < 4096)
+            if (_buffer.Length < MaxBufferSize)
             {
                 return;
             }
 
-            Array.Resize(ref _buffer, 4096);
+            Array.Resize(ref _buffer, MaxBufferSize);
         }
 
         private void EnsureAdditionalCapacity(int additionalCapacity)

Source/MQTTnet/Server/MqttClientSessionsManager.cs

@@ -148,7 +148,7 @@ namespace MQTTnet.Server
                         clientSession.EnqueueApplicationMessage(enqueuedApplicationMessage.Sender, applicationMessage);
                     }
                 }
-                catch (TaskCanceledException)
+                catch (OperationCanceledException)
                 {
                 }
                 catch (Exception exception)

Tests/MQTTnet.TestApp.UniversalWindows/MainPage.xaml

@@ -4,6 +4,8 @@
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    xmlns:server="using:MQTTnet.Server"
+    xmlns:interop="using:Windows.UI.Xaml.Interop"
     d:DesignHeight="800"
     d:DesignWidth="800"
     mc:Ignorable="d">
@@ -31,7 +33,7 @@
                     <CheckBox x:Name="CleanSession" IsChecked="True"></CheckBox>
                     <TextBlock>Keep alive interval:</TextBlock>
                     <TextBox x:Name="KeepAliveInterval" Text="5"></TextBox>
-                    
+
                     <StackPanel Orientation="Horizontal">
                         <RadioButton x:Name="UseTcp" IsChecked="True" GroupName="connection">TCP</RadioButton>
                         <RadioButton x:Name="UseWs" GroupName="connection">WS</RadioButton>
@@ -142,6 +144,7 @@
 
                     <CheckBox x:Name="ServerPersistRetainedMessages" IsChecked="True">Persist retained messages in JSON format</CheckBox>
                     <CheckBox x:Name="ServerClearRetainedMessages">Clear previously retained messages on startup</CheckBox>
+                    <CheckBox x:Name="ServerAllowPersistentSessions">Allow persistent sessions</CheckBox>
 
                     <StackPanel Orientation="Horizontal">
                         <Button Width="120" Margin="0,0,10,0" Click="StartServer">Start</Button>
@@ -149,11 +152,6 @@
                     </StackPanel>
                 </StackPanel>
             </PivotItem>
-            <PivotItem Header="Log">
-                <StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
-                    <Button Click="ClearLog" Width="120">Clear</Button>
-                </StackPanel>
-            </PivotItem>
 
             <PivotItem Header="Sessions">
                 <StackPanel Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
@@ -162,12 +160,23 @@
                         <Button Width="120" Margin="0,0,10,0" Click="ClearSessions">Clear</Button>
                     </StackPanel>
 
-                    <ListView>
+                    <ListView ItemsSource="{Binding}" x:Name="ListViewSessions">
                         <ListView.ItemTemplate>
-                            <DataTemplate>
+                            <DataTemplate x:DataType="server:IMqttClientSessionStatus">
-                                <Grid>
+                                <StackPanel Orientation="Horizontal">
-                                    <TextBlock></TextBlock>
+                                    <StackPanel.Resources>
-                                </Grid>
+                                        <Style TargetType="TextBlock">
+                                            <Setter Property="Margin" Value="0,0,10,0"></Setter>
+                                        </Style>
+                                    </StackPanel.Resources>
+                                    <TextBlock Text="{Binding ClientId}"></TextBlock>
+                                    <TextBlock Text="{Binding Endpoint}"></TextBlock>
+                                    <TextBlock Text="{Binding IsConnected}"></TextBlock>
+                                    <TextBlock Text="{Binding LastPacketReceived}"></TextBlock>
+                                    <TextBlock Text="{Binding LastNonKeepAlivePacketReceived}"></TextBlock>
+                                    <TextBlock Text="{Binding ProtocolVersion}"></TextBlock>
+                                    <TextBlock Text="{Binding PendingApplicationMessagesCount}"></TextBlock>
+                                </StackPanel>
                             </DataTemplate>
                         </ListView.ItemTemplate>
                     </ListView>

Tests/MQTTnet.TestApp.UniversalWindows/MainPage.xaml.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Concurrent;
+using System.Collections.ObjectModel;
 using System.Text;
 using System.Threading.Tasks;
 using Windows.Security.Cryptography.Certificates;
@@ -21,6 +22,7 @@ namespace MQTTnet.TestApp.UniversalWindows
     public sealed partial class MainPage
     {
         private readonly ConcurrentQueue<MqttNetLogMessage> _traceMessages = new ConcurrentQueue<MqttNetLogMessage>();
+        private readonly ObservableCollection<IMqttClientSessionStatus> _sessions = new ObservableCollection<IMqttClientSessionStatus>();
 
         private IMqttClient _mqttClient;
         private IMqttServer _mqttServer;
@@ -306,6 +308,7 @@ namespace MQTTnet.TestApp.UniversalWindows
             var options = new MqttServerOptions();
             options.DefaultEndpointOptions.Port = int.Parse(ServerPort.Text);
             options.Storage = storage;
+            options.EnablePersistentSessions = ServerAllowPersistentSessions.IsChecked == true;
 
             await _mqttServer.StartAsync(options);
         }
@@ -374,10 +377,25 @@ namespace MQTTnet.TestApp.UniversalWindows
 
         private void ClearSessions(object sender, RoutedEventArgs e)
         {
+            _sessions.Clear();
         }
 
-        private void RefreshSessions(object sender, RoutedEventArgs e)
+        private async void RefreshSessions(object sender, RoutedEventArgs e)
         {
+            if (_mqttServer == null)
+            {
+                return;
+            }
+
+            var sessions = await _mqttServer.GetClientSessionsStatusAsync();
+            _sessions.Clear();
+
+            foreach (var session in sessions)
+            {
+                _sessions.Add(session);
+            }
+
+            ListViewSessions.DataContext = _sessions;
         }
 
         private async Task WikiCode()