Android: create Pause/ResumeSem semaphore at higher level than CreateWindow()

- If you call onPause() before CreateWindow(), SDLThread will run in infinite loop in background.

- If you call onPause() between a DestroyWindow() and a new CreateWindow(), semaphores are invalids.

SDLActivity.java: the first resume() starts the SDLThread, don't call
nativeResume() as it would post ResumeSem. And the first pause would
automatically be resumed.

android-project/app/src/main/java/org/libsdl/app/SDLActivity.java

@@ -505,10 +505,14 @@ public class SDLActivity extends Activity implements View.OnSystemUiVisibilityCh
                     mSDLThread = new Thread(new SDLMain(), "SDLThread");
                     mSurface.enableSensor(Sensor.TYPE_ACCELEROMETER, true);
                     mSDLThread.start();
+                    
+                    // No nativeResume(), don't signal Android_ResumeSem
+                    mSurface.handleResume();
+                } else {
+                    nativeResume();
+                    mSurface.handleResume();
                 }
 
-                nativeResume();
-                mSurface.handleResume();
                 mCurrentNativeState = mNextNativeState;
             }
         }

src/core/android/SDL_android.c

@@ -439,6 +439,17 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(nativeSetupJNI)(JNIEnv *env, jclass cl
         __android_log_print(ANDROID_LOG_ERROR, "SDL", "failed to create Android_ActivityMutex mutex");
     }
 
+
+    Android_PauseSem = SDL_CreateSemaphore(0);
+    if (Android_PauseSem == NULL) {
+        __android_log_print(ANDROID_LOG_ERROR, "SDL", "failed to create Android_PauseSem semaphore");
+    }
+
+    Android_ResumeSem = SDL_CreateSemaphore(0);
+    if (Android_ResumeSem == NULL) {
+        __android_log_print(ANDROID_LOG_ERROR, "SDL", "failed to create Android_ResumeSem semaphore");
+    }
+
     mActivityClass = (jclass)((*env)->NewGlobalRef(env, cls));
 
     midGetNativeSurface = (*env)->GetStaticMethodID(env, mActivityClass,
@@ -961,6 +972,16 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(nativeQuit)(
         Android_ActivityMutex = NULL;
     }
 
+    if (Android_PauseSem) {
+        SDL_DestroySemaphore(Android_PauseSem);
+        Android_PauseSem = NULL;
+    }
+
+    if (Android_ResumeSem) {
+        SDL_DestroySemaphore(Android_ResumeSem);
+        Android_ResumeSem = NULL;
+    }
+
     str = SDL_GetError();
     if (str && str[0]) {
         __android_log_print(ANDROID_LOG_ERROR, "SDL", "SDLActivity thread ends (error=%s)", str);
@@ -982,14 +1003,14 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(nativePause)(
         SDL_SendWindowEvent(Android_Window, SDL_WINDOWEVENT_MINIMIZED, 0, 0);
         SDL_SendAppEvent(SDL_APP_WILLENTERBACKGROUND);
         SDL_SendAppEvent(SDL_APP_DIDENTERBACKGROUND);
-
-        /* *After* sending the relevant events, signal the pause semaphore
-         * so the event loop knows to pause and (optionally) block itself.
-         * Sometimes 2 pauses can be queued (eg pause/resume/pause), so it's
-         * always increased. */
-        SDL_SemPost(Android_PauseSem);
     }
 
+    /* *After* sending the relevant events, signal the pause semaphore
+     * so the event loop knows to pause and (optionally) block itself.
+     * Sometimes 2 pauses can be queued (eg pause/resume/pause), so it's
+     * always increased. */
+    SDL_SemPost(Android_PauseSem);
+
     SDL_UnlockMutex(Android_ActivityMutex);
 }
 
@@ -1006,13 +1027,14 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(nativeResume)(
         SDL_SendAppEvent(SDL_APP_DIDENTERFOREGROUND);
         SDL_SendWindowEvent(Android_Window, SDL_WINDOWEVENT_FOCUS_GAINED, 0, 0);
         SDL_SendWindowEvent(Android_Window, SDL_WINDOWEVENT_RESTORED, 0, 0);
-        /* Signal the resume semaphore so the event loop knows to resume and restore the GL Context
-         * We can't restore the GL Context here because it needs to be done on the SDL main thread
-         * and this function will be called from the Java thread instead.
-         */
-        SDL_SemPost(Android_ResumeSem);
     }
 
+    /* Signal the resume semaphore so the event loop knows to resume and restore the GL Context
+     * We can't restore the GL Context here because it needs to be done on the SDL main thread
+     * and this function will be called from the Java thread instead.
+     */
+    SDL_SemPost(Android_ResumeSem);
+
     SDL_UnlockMutex(Android_ActivityMutex);
 }
 

src/video/android/SDL_androidwindow.c

@@ -49,9 +49,6 @@ Android_CreateWindow(_THIS, SDL_Window * window)
         goto endfunction;
     }
 
-    Android_PauseSem = SDL_CreateSemaphore(0);
-    Android_ResumeSem = SDL_CreateSemaphore(0);
-
     /* Set orientation */
     Android_JNI_SetOrientation(window->w, window->h, window->flags & SDL_WINDOW_RESIZABLE, SDL_GetHint(SDL_HINT_ORIENTATIONS));
 
@@ -171,10 +168,6 @@ Android_DestroyWindow(_THIS, SDL_Window *window)
 
     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;