Merge pull request AvaloniaUI#8538 from AvaloniaUI/feature/expose-gtk…

…-thread-invoke

Introduced GtkInteropHelper.RunOnGlibThread, fixed demos
# Conflicts:
#	samples/ControlCatalog.NetCore/NativeControls/Gtk/EmbedSample.Gtk.cs
#	samples/ControlCatalog.NetCore/NativeControls/Gtk/GtkHelper.cs

src/Avalonia.X11/Interop/GtkInteropHelper.cs

@@ -0,0 +1,15 @@
+using System;
+using System.ComponentModel;
+using System.Threading.Tasks;
+
+namespace Avalonia.X11.Interop;
+
+public class GtkInteropHelper
+{
+    public static async Task<T> RunOnGlibThread<T>(Func<T> cb)
+    {
+        if (!await NativeDialogs.Gtk.StartGtk().ConfigureAwait(false))
+            throw new Win32Exception("Unable to initialize GTK");
+        return await NativeDialogs.Glib.RunOnGlibThread(cb).ConfigureAwait(false);
+    }
+}

src/Avalonia.X11/NativeDialogs/Gtk.cs

@@ -3,6 +3,8 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Avalonia.Platform.Interop;
+using JetBrains.Annotations;
+
 // ReSharper disable IdentifierTypo
 namespace Avalonia.X11.NativeDialogs
 {
@@ -247,10 +249,19 @@ public static extern void
 
         public static IntPtr GetForeignWindow(IntPtr xid) => gdk_x11_window_foreign_new_for_display(s_display, xid);
 
+        static object s_startGtkLock = new();
+        static Task<bool> s_startGtkTask;
+
         public static Task<bool> StartGtk()
         {
-            var tcs = new TaskCompletionSource<bool>();
-            new Thread(() =>
+            return StartGtkCore();
+            lock (s_startGtkLock)
+                return s_startGtkTask ??= StartGtkCore();
+        }
+
+        private static void GtkThread(TaskCompletionSource<bool> tcs)
+        {
+            try
             {
                 try
                 {
@@ -284,7 +295,17 @@ public static Task<bool> StartGtk()
                 tcs.SetResult(true);
                 while (true)
                     gtk_main_iteration();
-            }) {Name = "GTK3THREAD", IsBackground = true}.Start();
+            }
+            catch
+            {
+                tcs.SetResult(false);
+            }
+        }
+
+        private static Task<bool> StartGtkCore()
+        {
+            var tcs = new TaskCompletionSource<bool>();
+            new Thread(() => GtkThread(tcs)) {Name = "GTK3THREAD", IsBackground = true}.Start();
             return tcs.Task;
         }
     }