Refactor serializer locking and thread instances.

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>
-                                <Grid>
-                                    <TextBlock></TextBlock>
-                                </Grid>
+                            <DataTemplate x:DataType="server:IMqttClientSessionStatus">
+                                <StackPanel Orientation="Horizontal">
+                                    <StackPanel.Resources>
+                                        <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()