GameActivity PATH: fix deadlocks in java callbacks after app destroyed

This ensures that any java Activity callbacks take into account the
possibility that the `android_app` may have already been marked
destroyed if `android_main` has returned - and so they mustn't block
and wait for a thread that is no longer running.

android-activity/build.rs

@@ -1,10 +1,7 @@
 #![allow(dead_code)]
 
 fn build_glue_for_game_activity() {
-    for f in [
-        "GameActivity.h",
-        "GameActivity.cpp",
-    ] {
+    for f in ["GameActivity.h", "GameActivity.cpp"] {
         println!("cargo:rerun-if-changed=game-activity-csrc/game-activity/{f}");
     }
     cc::Build::new()

android-activity/game-activity-csrc/game-activity/native_app_glue/android_native_app_glue.c

@@ -308,6 +308,15 @@ static void android_app_set_window(struct android_app* android_app,
                                    ANativeWindow* window) {
     LOGV("android_app_set_window called");
     pthread_mutex_lock(&android_app->mutex);
+
+    // NB: we have to consider that the native thread could have already
+    // (gracefully) exit (setting android_app->destroyed) and so we need
+    // to be careful to avoid a deadlock waiting for a thread that's
+    // already exit.
+    if (android_app->destroyed) {
+        pthread_mutex_unlock(&android_app->mutex);
+        return;
+    }
     if (android_app->pendingWindow != NULL) {
         android_app_write_cmd(android_app, APP_CMD_TERM_WINDOW);
     }
@@ -324,15 +333,30 @@ static void android_app_set_window(struct android_app* android_app,
 static void android_app_set_activity_state(struct android_app* android_app,
                                            int8_t cmd) {
     pthread_mutex_lock(&android_app->mutex);
-    android_app_write_cmd(android_app, cmd);
-    while (android_app->activityState != cmd) {
-        pthread_cond_wait(&android_app->cond, &android_app->mutex);
+
+    // NB: we have to consider that the native thread could have already
+    // (gracefully) exit (setting android_app->destroyed) and so we need
+    // to be careful to avoid a deadlock waiting for a thread that's
+    // already exit.
+    if (!android_app->destroyed) {
+        android_app_write_cmd(android_app, cmd);
+        while (android_app->activityState != cmd) {
+            pthread_cond_wait(&android_app->cond, &android_app->mutex);
+        }
     }
     pthread_mutex_unlock(&android_app->mutex);
 }
 
 static void android_app_free(struct android_app* android_app) {
     pthread_mutex_lock(&android_app->mutex);
+
+    // It's possible that onDestroy is called after we have already 'destroyed'
+    // the app (via `android_app_destroy` due to `android_main` returning.
+    //
+    // In this case `->destroyed` will already be set (so we won't deadlock in
+    // the loop below) but we still need to close the messaging fds and finish
+    // freeing the android_app
+
     android_app_write_cmd(android_app, APP_CMD_DESTROY);
     while (!android_app->destroyed) {
         pthread_cond_wait(&android_app->cond, &android_app->mutex);
@@ -372,6 +396,16 @@ static void onSaveInstanceState(GameActivity* activity,
 
     struct android_app* android_app = ToApp(activity);
     pthread_mutex_lock(&android_app->mutex);
+
+    // NB: we have to consider that the native thread could have already
+    // (gracefully) exit (setting android_app->destroyed) and so we need
+    // to be careful to avoid a deadlock waiting for a thread that's
+    // already exit.
+    if (android_app->destroyed) {
+        pthread_mutex_unlock(&android_app->mutex);
+        return;
+    }
+
     android_app->stateSaved = 0;
     android_app_write_cmd(android_app, APP_CMD_SAVE_STATE);
     while (!android_app->stateSaved) {
@@ -481,6 +515,15 @@ static bool onTouchEvent(GameActivity* activity,
     struct android_app* android_app = ToApp(activity);
     pthread_mutex_lock(&android_app->mutex);
 
+    // NB: we have to consider that the native thread could have already
+    // (gracefully) exit (setting android_app->destroyed) and so we need
+    // to be careful to avoid a deadlock waiting for a thread that's
+    // already exit.
+    if (android_app->destroyed) {
+        pthread_mutex_unlock(&android_app->mutex);
+        return false;
+    }
+
     if (android_app->motionEventFilter != NULL &&
         !android_app->motionEventFilter(event)) {
         pthread_mutex_unlock(&android_app->mutex);
@@ -563,6 +606,15 @@ static bool onKey(GameActivity* activity, const GameActivityKeyEvent* event) {
     struct android_app* android_app = ToApp(activity);
     pthread_mutex_lock(&android_app->mutex);
 
+    // NB: we have to consider that the native thread could have already
+    // (gracefully) exit (setting android_app->destroyed) and so we need
+    // to be careful to avoid a deadlock waiting for a thread that's
+    // already exit.
+    if (android_app->destroyed) {
+        pthread_mutex_unlock(&android_app->mutex);
+        return false;
+    }
+
     if (android_app->keyEventFilter != NULL &&
         !android_app->keyEventFilter(event)) {
         pthread_mutex_unlock(&android_app->mutex);
@@ -599,8 +651,9 @@ static void onTextInputEvent(GameActivity* activity,
                              const GameTextInputState* state) {
     struct android_app* android_app = ToApp(activity);
     pthread_mutex_lock(&android_app->mutex);
-
-    android_app->textInputState = 1;
+    if (!android_app->destroyed) {
+        android_app->textInputState = 1;
+    }
     pthread_mutex_unlock(&android_app->mutex);
 }