Android: prevents rare crashes when app goes to background or ends.

Make sure the thread is actually paused, and context backep-up, before
SurfaceView is destroyed (eg surfaceDestroyed() actually returns).

Add a timeout when surfaceDestroyed() is called, and check 'backup_done' variable.

It prevents crashes like:

  #00  pc 000000000000c0d0  /system/lib64/libutils.so (android::RefBase::incStrong(void const*) const+8)
  #01  pc 000000000000c7f4  /vendor/lib64/egl/eglSubDriverAndroid.so (EglAndroidWindowSurface::UpdateBufferList(ANativeWindowBuffer*)+284)
  #02  pc 000000000000c390  /vendor/lib64/egl/eglSubDriverAndroid.so (EglAndroidWindowSurface::DequeueBuffer()+240)
  #03  pc 000000000000bb10  /vendor/lib64/egl/eglSubDriverAndroid.so (EglAndroidWindowSurface::GetBuffer(EglSubResource*, EglMemoryDesc*)+64)
  #04  pc 000000000032732c  /vendor/lib64/egl/libGLESv2_adreno.so (EglWindowSurface::UpdateResource(EsxContext*)+116)
  #05  pc 0000000000326dd0  /vendor/lib64/egl/libGLESv2_adreno.so (EglWindowSurface::GetResource(EsxContext*, EsxResource**, EsxResource**, int)+56)
  #06  pc 00000000002ae484  /vendor/lib64/egl/libGLESv2_adreno.so (EsxContext::AcquireBackBuffer(int)+364)
  #07  pc 0000000000249680  /vendor/lib64/egl/libGLESv2_adreno.so (EsxContext::Clear(unsigned int, unsigned int, unsigned int, EsxClearValues*)+1800)
  #08  pc 00000000002cb52c  /vendor/lib64/egl/libGLESv2_adreno.so (EsxGlApiParamValidate::GlClear(EsxDispatch*, unsigned int)+132)

src/core/android/SDL_android.c

@@ -994,6 +994,10 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(onNativeSurfaceChanged)(JNIEnv *env, j
 /* Called from surfaceDestroyed() */
 JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(onNativeSurfaceDestroyed)(JNIEnv *env, jclass jcls)
 {
+    int nb_attempt = 50;
+
+retry:
+
     SDL_LockMutex(Android_ActivityMutex);
 
     if (Android_Window)
@@ -1001,21 +1005,27 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(onNativeSurfaceDestroyed)(JNIEnv *env,
         SDL_VideoDevice *_this = SDL_GetVideoDevice();
         SDL_WindowData  *data  = (SDL_WindowData *) Android_Window->driverdata;
 
-        /* We have to clear the current context and destroy the egl surface here
-         * Otherwise there's BAD_NATIVE_WINDOW errors coming from eglCreateWindowSurface on resume
-         * Ref: http://stackoverflow.com/questions/8762589/eglcreatewindowsurface-on-ics-and-switching-from-2d-to-3d
-         */
+        /* Wait for Main thread being paused and context un-activated to release 'egl_surface' */
+        if (! data->backup_done) {
+            nb_attempt -= 1;
+            if (nb_attempt == 0) {
+                SDL_SetError("Try to release egl_surface with context probably still active");
+            } else {
+                SDL_UnlockMutex(Android_ActivityMutex);
+                SDL_Delay(10);
+                goto retry;
+            }
+        }
 
         if (data->egl_surface != EGL_NO_SURFACE) {
-            SDL_EGL_MakeCurrent(_this, NULL, NULL);
             SDL_EGL_DestroySurface(_this, data->egl_surface);
             data->egl_surface = EGL_NO_SURFACE;
         }
 
         if (data->native_window) {
             ANativeWindow_release(data->native_window);
-        }
             data->native_window = NULL;
+        }
 
         /* GL Context handling is done in the event loop because this function is run from the Java thread */
     }

src/video/android/SDL_androidevents.c

@@ -68,6 +68,7 @@ android_egl_context_restore(SDL_Window *window)
             event.type = SDL_RENDER_DEVICE_RESET;
             SDL_PushEvent(&event);
         }
+        data->backup_done = 0;
     }
 }
 
@@ -80,6 +81,7 @@ android_egl_context_backup(SDL_Window *window)
         data->egl_context = SDL_GL_GetCurrentContext();
         /* We need to do this so the EGLSurface can be freed */
         SDL_GL_MakeCurrent(window, NULL);
+        data->backup_done = 1;
     }
 }
 

src/video/android/SDL_androidwindow.h

@@ -39,6 +39,7 @@ typedef struct
 {
     EGLSurface egl_surface;
     EGLContext egl_context; /* We use this to preserve the context when losing focus */
+    SDL_bool   backup_done;
     ANativeWindow *native_window;
     
 } SDL_WindowData;