Fixed bug 4142 - Concurrency issues in Android backend

Use a semaphore to prevent concurrency issues between Java Activity and Native thread code, when using 'Android_Window'.
(Eg. Java sending Touch events, while native code is destroying the main SDL_Window. )

src/video/android/SDL_androidevents.c

@@ -39,8 +39,8 @@ static void ANDROIDAUDIO_ResumeDevices(void) {}
 static void ANDROIDAUDIO_PauseDevices(void) {}
 #endif
 
-static void 
-android_egl_context_restore(SDL_Window *window) 
+static void
+android_egl_context_restore(SDL_Window *window)
 {
     SDL_Event event;
     SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
@@ -53,8 +53,8 @@ android_egl_context_restore(SDL_Window *window)
     }
 }
 
-static void 
-android_egl_context_backup(SDL_Window *window) 
+static void
+android_egl_context_backup(SDL_Window *window)
 {
     /* Keep a copy of the EGL Context so we can try to restore it when we resume */
     SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
@@ -80,7 +80,10 @@ Android_PumpEvents(_THIS)
 #if SDL_ANDROID_BLOCK_ON_PAUSE
     if (isPaused && !isPausing) {
         /* Make sure this is the last thing we do before pausing */
+        SDL_SemWait(Android_ActivitySem);
         android_egl_context_backup(Android_Window);
+        SDL_SemPost(Android_ActivitySem);
+
         ANDROIDAUDIO_PauseDevices();
         if (SDL_SemWait(Android_ResumeSem) == 0) {
 #else
@@ -91,7 +94,9 @@ Android_PumpEvents(_THIS)
             ANDROIDAUDIO_ResumeDevices();
             /* Restore the GL Context from here, as this operation is thread dependent */
             if (!SDL_HasEvent(SDL_QUIT)) {
+                SDL_SemWait(Android_ActivitySem);
                 android_egl_context_restore(Android_Window);
+                SDL_SemPost(Android_ActivitySem);
             }
         }
     }
@@ -110,7 +115,10 @@ Android_PumpEvents(_THIS)
         }
 #else
         if (SDL_SemTryWait(Android_PauseSem) == 0) {
+            SDL_SemWait(Android_ActivitySem);
             android_egl_context_backup(Android_Window);
+            SDL_SemPost(Android_ActivitySem);
+
             ANDROIDAUDIO_PauseDevices();
             isPaused = 1;
         }

src/video/android/SDL_androidvideo.c

@@ -66,7 +66,7 @@ int Android_DeviceHeight = 0;
 static Uint32 Android_ScreenFormat = SDL_PIXELFORMAT_UNKNOWN;
 static int Android_ScreenRate = 0;
 
-SDL_sem *Android_PauseSem = NULL, *Android_ResumeSem = NULL;
+SDL_sem *Android_PauseSem = NULL, *Android_ResumeSem = NULL, *Android_ActivitySem = NULL;
 
 static int
 Android_Available(void)

src/video/android/SDL_androidvideo.h

@@ -41,7 +41,7 @@ extern int Android_SurfaceWidth;
 extern int Android_SurfaceHeight;
 extern int Android_DeviceWidth;
 extern int Android_DeviceHeight;
-extern SDL_sem *Android_PauseSem, *Android_ResumeSem;
+extern SDL_sem *Android_PauseSem, *Android_ResumeSem, *Android_ActivitySem;
 
 #endif /* SDL_androidvideo_h_ */
 

src/video/android/SDL_androidwindow.c

@@ -41,12 +41,14 @@ Android_CreateWindow(_THIS, SDL_Window * window)
 {
     SDL_WindowData *data;
     int retval = 0;
-    
+
+    SDL_SemWait(Android_ActivitySem);
+
     if (Android_Window) {
         retval = SDL_SetError("Android only supports one window");
         goto endfunction;
     }
-    
+
     Android_PauseSem = SDL_CreateSemaphore(0);
     Android_ResumeSem = SDL_CreateSemaphore(0);
 
@@ -67,15 +69,15 @@ Android_CreateWindow(_THIS, SDL_Window * window)
     /* One window, it always has focus */
     SDL_SetMouseFocus(window);
     SDL_SetKeyboardFocus(window);
-    
+
     data = (SDL_WindowData *) SDL_calloc(1, sizeof(*data));
     if (!data) {
         retval = SDL_OutOfMemory();
         goto endfunction;
     }
-    
+
     data->native_window = Android_JNI_GetNativeWindow();
-    
+
     if (!data->native_window) {
         SDL_free(data);
         retval = SDL_SetError("Could not fetch native window");
@@ -99,7 +101,9 @@ Android_CreateWindow(_THIS, SDL_Window * window)
     Android_Window = window;
 
 endfunction:
-    
+
+    SDL_SemPost(Android_ActivitySem);
+
     return retval;
 }
 
@@ -146,14 +150,16 @@ Android_SetWindowFullscreen(_THIS, SDL_Window *window, SDL_VideoDisplay *display
 
 void
 Android_DestroyWindow(_THIS, SDL_Window *window)
-{ 
+{
+    SDL_SemWait(Android_ActivitySem);
+
     if (window == Android_Window) {
         Android_Window = NULL;
         if (Android_PauseSem) SDL_DestroySemaphore(Android_PauseSem);
         if (Android_ResumeSem) SDL_DestroySemaphore(Android_ResumeSem);
         Android_PauseSem = NULL;
         Android_ResumeSem = NULL;
-        
+
         if (window->driverdata) {
             SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
             if (data->egl_surface != EGL_NO_SURFACE) {
@@ -166,6 +172,8 @@ Android_DestroyWindow(_THIS, SDL_Window *window)
             window->driverdata = NULL;
         }
     }
+
+    SDL_SemPost(Android_ActivitySem);
 }
 
 SDL_bool