[UI] Android CallInUIThread and activity onDestroy

src/xenia/ui/windowed_app_context_android.h

@@ -10,7 +10,9 @@
 #ifndef XENIA_UI_WINDOWED_APP_CONTEXT_ANDROID_H_
 #define XENIA_UI_WINDOWED_APP_CONTEXT_ANDROID_H_
 
+#include <android/looper.h>
 #include <android/native_activity.h>
+#include <array>
 #include <memory>
 
 #include "xenia/ui/windowed_app_context.h"
@@ -24,15 +26,11 @@ class WindowedApp;
 class AndroidWindowedAppContext final : public WindowedAppContext {
  public:
   // For calling from android.app.func_name exports.
-  static void StartAppOnNativeActivityCreate(
+  static void StartAppOnActivityCreate(
       ANativeActivity* activity, void* saved_state, size_t saved_state_size,
       std::unique_ptr<WindowedApp> (*app_creator)(
           WindowedAppContext& app_context));
 
-  // Defined in the translation unit where WindowedApp is complete because of
-  // std::unique_ptr.
-  ~AndroidWindowedAppContext();
-
   ANativeActivity* activity() const { return activity_; }
   WindowedApp* app() const { return app_.get(); }
 
@@ -48,21 +46,54 @@ class AndroidWindowedAppContext final : public WindowedAppContext {
   void SetActivityWindow(AndroidWindow* window) { activity_window_ = window; }
 
  private:
-  explicit AndroidWindowedAppContext(ANativeActivity* activity);
+  enum class UIThreadLooperCallbackCommand : uint8_t {
+    kDestroy,
+    kExecutePendingFunctions,
+  };
+
+  AndroidWindowedAppContext() = default;
+
+  // Don't delete this object directly externally if successfully initialized as
+  // the looper may still execute the callback for pending commands after an
+  // external ANativeActivity_removeFd, and the callback receives a pointer to
+  // the context - deletion must be deferred and done in the callback itself.
+  // Defined in the translation unit where WindowedApp is complete because of
+  // std::unique_ptr.
+  ~AndroidWindowedAppContext();
+
+  bool Initialize(ANativeActivity* activity);
+  void Shutdown();
+
+  // Call this function instead of deleting the object directly, so if needed,
+  // deletion will be deferred until the callback (receiving a pointer to the
+  // context) can no longer be executed by the looper (will be done inside the
+  // callback).
+  void RequestDestruction();
+
+  static int UIThreadLooperCallback(int fd, int events, void* data);
+
   bool InitializeApp(std::unique_ptr<WindowedApp> (*app_creator)(
       WindowedAppContext& app_context));
 
+  static void OnActivityDestroy(ANativeActivity* activity);
+
+  bool android_base_initialized_ = false;
+
+  // May be read by non-UI threads in NotifyUILoopOfPendingFunctions.
+  ALooper* ui_thread_looper_ = nullptr;
+  // [1] (the write file descriptor) may be referenced as read-only by non-UI
+  // threads in NotifyUILoopOfPendingFunctions.
+  std::array<int, 2> ui_thread_looper_callback_pipe_{-1, -1};
+  bool ui_thread_looper_callback_registered_ = false;
+
   // TODO(Triang3l): Switch from ANativeActivity to the context itself being the
   // object for communication with the Java code when NativeActivity isn't used
   // anymore as its functionality is heavily limited.
-  ANativeActivity* activity_;
-  std::unique_ptr<WindowedApp> app_;
+  ANativeActivity* activity_ = nullptr;
 
   AndroidWindow* activity_window_ = nullptr;
 
-  // TODO(Triang3l): The rest of the context, including quit handler (and the
-  // destructor) calling `finish` on the activity, UI looper notification
-  // posting, etc.
+  std::unique_ptr<WindowedApp> app_;
 };
 
 }  // namespace ui