Fix deadlock on activity onDestroy

Fix a deadlock that occurs when an activity is destroyed without process termination, such as when an activity is destroyed and recreated due to a configuration change.

The deadlock occurs because `notify_destroyed` blocks until `destroyed` is set to `true`. This only occurs when `WaitableNativeActivityState` is dropped, but the `WaitableNativeActivityState` instance is the very thing being used to await for destruction, resulting in a deadlock.

Author: sagebind

android-activity/src/native_activity/glue.rs

@@ -372,7 +372,7 @@ impl WaitableNativeActivityState {
 
         unsafe {
             guard.write_cmd(AppCmd::Destroy);
-            while !guard.destroyed {
+            while guard.running {
                 guard = self.cond.wait(guard).unwrap();
             }
 
@@ -545,6 +545,12 @@ impl WaitableNativeActivityState {
         self.cond.notify_one();
     }
 
+    pub fn notify_main_thread_stopped_running(&self) {
+        let mut guard = self.mutex.lock().unwrap();
+        guard.running = false;
+        self.cond.notify_one();
+    }
+
     pub unsafe fn pre_exec_cmd(
         &self,
         cmd: AppCmd,
@@ -907,6 +913,8 @@ extern "C" fn ANativeActivity_onCreate(
 
                 ndk_context::release_android_context();
             }
+
+            rust_glue.notify_main_thread_stopped_running();
         });
 
         // Wait for thread to start.