Use atomic fetch-and-add for unique window classes

src/wine-host/bridges/vst2.cpp

@@ -379,13 +379,7 @@ intptr_t Vst2Bridge::dispatch_wrapper(AEffect* plugin,
             // provided by the host, and let the plugin embed itself into
             // the Wine window
             const auto x11_handle = reinterpret_cast<size_t>(data);
-            // Win32 window classes have to be unique for the whole application.
-            // When hosting multiple plugins in a group process, all plugins
-            // should get a unique window class
-            const std::string window_class =
-                "yabridge plugin " + sockets.base_dir.string();
-            Editor& editor_instance =
-                editor.emplace(config, window_class, x11_handle);
+            Editor& editor_instance = editor.emplace(config, x11_handle);
 
             return plugin->dispatcher(plugin, opcode, index, value,
                                       editor_instance.get_win32_handle(),

src/wine-host/bridges/vst3.cpp

@@ -397,9 +397,6 @@ void Vst3Bridge::run() {
                 //       and if it's actually needed (for instance when the host
                 //       resizes the window without informing the plugin)
                 const auto x11_handle = static_cast<size_t>(request.parent);
-                const std::string window_class =
-                    "yabridge plugin " + sockets.base_dir.string() + " " +
-                    std::to_string(request.owner_instance_id);
 
                 // Creating the window and having the plugin embed in it should
                 // be done in the main UI thread
@@ -407,8 +404,7 @@ void Vst3Bridge::run() {
                     .run_in_context<tresult>([&]() {
                         Editor& editor_instance =
                             object_instances[request.owner_instance_id]
-                                .editor.emplace(config, window_class,
-                                                x11_handle);
+                                .editor.emplace(config, x11_handle);
 
                         const tresult result =
                             object_instances[request.owner_instance_id]

src/wine-host/editor.cpp

@@ -45,6 +45,12 @@ constexpr uint32_t xembed_focus_in_msg = 4;
 
 constexpr uint32_t xembed_focus_first = 1;
 
+/**
+ * Used to generate a globally unique identifier for a window class. This is
+ * needed because every window's window class name should be unique.
+ */
+std::atomic_size_t window_class_id{};
+
 /**
  * Find the topmost window (i.e. the window before the root window in the window
  * tree) starting from a certain window.
@@ -94,13 +100,12 @@ WindowClass::~WindowClass() {
     UnregisterClass(reinterpret_cast<LPCSTR>(atom), GetModuleHandle(nullptr));
 }
 
-Editor::Editor(const Configuration& config,
-               const std::string& window_class_name,
-               const size_t parent_window_handle)
+Editor::Editor(const Configuration& config, const size_t parent_window_handle)
     : use_xembed(config.editor_xembed),
       x11_connection(xcb_connect(nullptr, nullptr), xcb_disconnect),
       client_area(get_maximum_screen_dimensions(*x11_connection)),
-      window_class(window_class_name),
+      window_class("yabridge plugin " +
+                   std::to_string(window_class_id.fetch_add(1))),
       // Create a window without any decoratiosn for easy embedding. The
       // combination of `WS_EX_TOOLWINDOW` and `WS_POPUP` causes the window to
       // be drawn without any decorations (making resizes behave as you'd

src/wine-host/editor.h

@@ -97,16 +97,12 @@ class Editor {
      *
      * @param config This instance's configuration, used to enable alternative
      *   editor behaviours.
-     * @param window_class_name The name for the window class for editor
-     *   windows.
      * @param parent_window_handle The X11 window handle passed by the VST host
      *   for the editor to embed itself into.
      *
      * @see win32_handle
      */
-    Editor(const Configuration& config,
-           const std::string& window_class_name,
-           const size_t parent_window_handle);
+    Editor(const Configuration& config, const size_t parent_window_handle);
 
     ~Editor();