Separate UI thread dedicated for the KeeAgent Plugin UI interactions

KeeAgent/KeeAgent.csproj

@@ -139,6 +139,7 @@
       <DependentUpon>ManageDialog.cs</DependentUpon>
     </Compile>
     <Compile Include="KeeAgentExt.cs" />
+    <Compile Include="KeeAgentInteractiveUi.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="UI\OptionsPanel.cs">
       <SubType>UserControl</SubType>

KeeAgent/KeeAgentExt.cs

@@ -26,7 +26,6 @@
 using KeePass.Util.Spr;
 using KeePassLib;
 using KeePassLib.Utility;
-using SshAgentLib.Keys;
 
 namespace KeeAgent
 {
@@ -43,6 +42,7 @@ public sealed partial class KeeAgentExt : Plugin
     bool saveBeforeCloseQuestionMessageShown = false;
     Dictionary<string, KeyFileInfo> keyFileMap = new Dictionary<string, KeyFileInfo>();
     KeeAgentColumnProvider columnProvider;
+    KeeAgentInteractiveUi interactiveUi;
 
     const string pluginNamespace = "KeeAgent";
     const string alwaysConfirmOptionName = pluginNamespace + ".AlwaysConfirm";
@@ -103,6 +103,7 @@ public override bool Initialize(IPluginHost host)
       var domainSocketPath =
         Environment.GetEnvironmentVariable(UnixClient.SshAuthSockName);
       try {
+        interactiveUi = new KeeAgentInteractiveUi();
         if (Options.AgentMode != AgentMode.Client) {
           if (isWindows) {
             // In windows, try to start an agent. If Pageant is running, we will
@@ -213,9 +214,7 @@ private bool ConfirmUserPermissionCallback(ISshKey key, Process process, string
       string toHost)
     {
       var result = false;
-      pluginHost.MainWindow.Invoke(new Action(() =>
-        result = Default.ConfirmCallback(key, process, user, fromHost, toHost)
-      ));
+      interactiveUi.Invoke(() => result = Default.ConfirmCallback(key, process, user, fromHost, toHost));
       return result;
     }
 
@@ -237,6 +236,10 @@ public override void Terminate()
         // need to shutdown agent or app won't exit
         agentModeAgent.Dispose();
       }
+
+      if (interactiveUi != null) {
+        interactiveUi.Dispose();
+      }
     }
 
     public override Image SmallIcon {
@@ -1238,22 +1241,20 @@ IEnumerable<ISshKey> FilterKeyList(IEnumerable<ISshKey> list)
         return list;
       }
 
-      // TODO: Using the main thread here will cause a lockup with IOProtocolExt
-      pluginHost.MainWindow.Invoke((MethodInvoker)delegate {
+      interactiveUi.Invoke(() => {
         //var zIndex = pluginHost.MainWindow.GetZIndex();
         var dialog = new KeyPicker(list);
         dialog.Shown += (sender, e) => dialog.Activate();
+        dialog.StartPosition = FormStartPosition.CenterScreen;
         dialog.TopMost = true;
-        dialog.ShowDialog(pluginHost.MainWindow);
+        dialog.ShowDialog();
 
         if (dialog.DialogResult == DialogResult.OK) {
           list = dialog.SelectedKeys.ToList();
         }
         else {
           list = Enumerable.Empty<ISshKey>();
         }
-
-        pluginHost.MainWindow.SetWindowPosBottom();
       });
 
       return list;

KeeAgent/KeeAgentInteractiveUi.cs

@@ -0,0 +1,79 @@
+using System;
+using System.Threading;
+using System.Windows.Forms;
+
+namespace KeeAgent
+{
+  /// <summary>
+  /// Provides a separate UI thread for interactive communication without interlocking with the MainWindow.
+  /// </summary>
+  public sealed class KeeAgentInteractiveUi : IDisposable
+  {
+    private const string ComponentName = "KeeAgent Interactive UI";
+    private SynchronizationContext _synchronizationContext;
+    private ApplicationContext _applicationContext;
+
+    public KeeAgentInteractiveUi()
+    {
+      var uiThread = new Thread(UiThreadMain) {
+        Name = ComponentName,
+        IsBackground = true // active background thread will not block the application shutdown process
+      };
+      uiThread.SetApartmentState(ApartmentState.STA);
+      uiThread.Start();
+    }
+
+    private void UiThreadMain()
+    {
+      var mainForm = new Form {
+        // actually we don't need the window, but there is no other way to capture the SynchronizationContext
+        Name = ComponentName,
+        Text = ComponentName,
+        // some recommendations from https://stackoverflow.com/a/683991
+        FormBorderStyle = FormBorderStyle.FixedToolWindow, // to exclude from appearing in Alt-Tab
+        ShowInTaskbar = false, // to exclude from the Taskbar
+      };
+
+      mainForm.Load += (sender, args) => {
+        // capture SynchronizationContext to send messages to the message loop
+        _synchronizationContext = SynchronizationContext.Current;
+
+        // hide the form... we have to postpone the call, otherwise it stays visible
+        _synchronizationContext.Post(_ => mainForm.Hide(), null);
+      };
+
+      _applicationContext = new ApplicationContext(mainForm);
+      Application.Run(_applicationContext);
+    }
+
+    /// <summary>
+    /// Performs message loop shutdown.
+    /// </summary>
+    public void Dispose()
+    {
+      if (_synchronizationContext == null) {
+        return;
+      }
+
+      var synchronizationContext = _synchronizationContext;
+      _synchronizationContext = null;
+      synchronizationContext.Post(_ => _applicationContext.ExitThread(), null);
+    }
+
+    /// <summary>
+    /// Invokes a delegate on a separate UI Thread, dedicated for the KeeAgent Plugin
+    /// </summary>
+    /// <param name="action">The delegate to call.</param>
+    /// <exception cref="InvalidOperationException">The method was called in while the SynchronizationContext is not
+    /// captured yet or have been disposed already</exception>
+    public void Invoke(Action action)
+    {
+      if (_synchronizationContext == null) {
+        throw new InvalidOperationException(
+          "KeeAgentInteractiveUi: the SynchronizationContext is not captured yet or have been disposed already");
+      }
+
+      _synchronizationContext.Send(_ => action.Invoke(), null);
+    }
+  }
+}