Fix GUI related data races within Serum

src/wine-host/editor.h

@@ -13,6 +13,7 @@
 #include <windows.h>
 
 #include <memory>
+#include <mutex>
 #include <optional>
 #include <string>
 
@@ -43,6 +44,8 @@ class Editor {
      *   windows.
      * @param effect The plugin this window is being created for. Used to send
      *   `effEditIdle` messages on a timer.
+     * @param processing_mutex The mutex belonging to `effect` audio processing
+     *   routine.
      * @param parent_window_handle The X11 window handle passed by the VST host
      *   for the editor to embed itself into.
      *
@@ -50,16 +53,22 @@ class Editor {
      */
     Editor(const std::string& window_class_name,
            AEffect* effect,
+           std::mutex& processing_mutex,
            const size_t parent_window_handle);
 
+    /**
+     * Send a single `effEditIdle` event to the plugin to allow it to update its
+     * GUI state. This is called periodically from a timer while the GUI is
+     * being blocked.
+     */
+    void send_idle_event();
+
     /**
      * Pump messages from the editor GUI's event loop until all events are
      * process. Must be run from the same thread the GUI was created in because
      * of Win32 limitations. I guess that's what `effEditIdle` is for.
      */
     void handle_events();
-    // Needed to handle idle updates through a timer
-    AEffect* plugin;
 
    private:
     /**
@@ -76,6 +85,14 @@ class Editor {
         win32_handle;
 
    private:
+    /**
+     * Run the win32 message handling loop, filtering out the events generated
+     * by the `effEditIdle` timer since those are sent manually on every
+     * invocation of `handle_events()` to match the `effEditIdle` events sent by
+     * the DAW.
+     */
+    void win32_event_loop();
+
     /**
      * The window handle of the editor window created by the DAW.
      */
@@ -85,10 +102,19 @@ class Editor {
      */
     xcb_window_t child_window;
 
+    /**
+     *Needed to handle idle updates through a timer
+     */
+    AEffect* plugin;
+    /**
+     * The mutex belonging to `plugin`'s audio processing routine, see
+     * `PluginBridge::processing_mutex`'s docstring for more information.
+     */
+    std::mutex& processing_mutex;
+
     /**
      * A pointer to the currently active window. Will be a null pointer if no
      * window is active.
      */
-
     std::unique_ptr<xcb_connection_t, decltype(&xcb_disconnect)> x11_connection;
 };