Protect against reentrancy (messily)

src/platform_impl/macos/app_state.rs

@@ -82,11 +82,13 @@ where
 #[derive(Default)]
 struct Handler {
     ready: AtomicBool,
+    in_callback: AtomicBool,
     control_flow: Mutex<ControlFlow>,
     control_flow_prev: Mutex<ControlFlow>,
     start_time: Mutex<Option<Instant>>,
     callback: Mutex<Option<Box<dyn EventHandler>>>,
     pending_events: Mutex<VecDeque<Event<Never>>>,
+    deferred_events: Mutex<VecDeque<Event<Never>>>,
     pending_redraw: Mutex<Vec<WindowId>>,
     waker: Mutex<EventLoopWaker>,
 }
@@ -99,6 +101,10 @@ impl Handler {
         self.pending_events.lock().unwrap()
     }
 
+    fn deferred<'a>(&'a self) -> MutexGuard<'a, VecDeque<Event<Never>>> {
+        self.deferred_events.lock().unwrap()
+    }
+
     fn redraw<'a>(&'a self) -> MutexGuard<'a, Vec<WindowId>> {
         self.pending_redraw.lock().unwrap()
     }
@@ -143,10 +149,22 @@ impl Handler {
         mem::replace(&mut *self.events(), Default::default())
     }
 
+    fn take_deferred(&self) -> VecDeque<Event<Never>> {
+        mem::replace(&mut *self.deferred(), Default::default())
+    }
+
     fn should_redraw(&self) -> Vec<WindowId> {
         mem::replace(&mut *self.redraw(), Default::default())
     }
 
+    fn get_in_callback(&self) -> bool {
+        self.in_callback.load(Ordering::Acquire)
+    }
+
+    fn set_in_callback(&self, in_callback: bool) {
+        self.in_callback.store(in_callback, Ordering::Release);
+    }
+
     fn handle_nonuser_event(&self, event: Event<Never>) {
         if let Some(ref mut callback) = *self.callback.lock().unwrap() {
             callback.handle_nonuser_event(
@@ -181,13 +199,17 @@ impl AppState {
     }
 
     pub fn exit() {
+        HANDLER.set_in_callback(true);
         HANDLER.handle_nonuser_event(Event::LoopDestroyed);
+        HANDLER.set_in_callback(false);
     }
 
     pub fn launched() {
         HANDLER.set_ready();
         HANDLER.waker().start();
+        HANDLER.set_in_callback(true);
         HANDLER.handle_nonuser_event(Event::NewEvents(StartCause::Init));
+        HANDLER.set_in_callback(false);
     }
 
     pub fn wakeup() {
@@ -214,7 +236,9 @@ impl AppState {
             },
             ControlFlow::Exit => StartCause::Poll,//panic!("unexpected `ControlFlow::Exit`"),
         };
+        HANDLER.set_in_callback(true);
         HANDLER.handle_nonuser_event(Event::NewEvents(cause));
+        HANDLER.set_in_callback(false);
     }
 
     // This is called from multiple threads at present
@@ -227,38 +251,49 @@ impl AppState {
 
     pub fn queue_event(event: Event<Never>) {
         if !unsafe { msg_send![class!(NSThread), isMainThread] } {
-            panic!("uh-oh");
+            panic!("Event queued from different thread: {:#?}", event);
         }
         HANDLER.events().push_back(event);
     }
 
     pub fn queue_events(mut events: VecDeque<Event<Never>>) {
         if !unsafe { msg_send![class!(NSThread), isMainThread] } {
-            panic!("uh-ohs");
+            panic!("Events queued from different thread: {:#?}", events);
         }
         HANDLER.events().append(&mut events);
     }
 
     pub fn send_event_immediately(event: Event<Never>) {
         if !unsafe { msg_send![class!(NSThread), isMainThread] } {
-            panic!("uh-oh");
+            panic!("Event sent from different thread: {:#?}", event);
+        }
+        HANDLER.deferred().push_back(event);
+        if !HANDLER.get_in_callback() {
+            HANDLER.set_in_callback(true);
+            for event in HANDLER.take_deferred() {
+                HANDLER.handle_nonuser_event(event);
+            }
+            HANDLER.set_in_callback(false);
         }
-        HANDLER.handle_nonuser_event(event);
     }
 
     pub fn cleared() {
         if !HANDLER.is_ready() { return }
-        HANDLER.handle_user_events();
-        for event in HANDLER.take_events() {
-            HANDLER.handle_nonuser_event(event);
-        }
-        for window_id in HANDLER.should_redraw() {
-            HANDLER.handle_nonuser_event(Event::WindowEvent {
-                window_id,
-                event: WindowEvent::RedrawRequested,
-            });
+        if !HANDLER.get_in_callback() {
+            HANDLER.set_in_callback(true);
+            HANDLER.handle_user_events();
+            for event in HANDLER.take_events() {
+                HANDLER.handle_nonuser_event(event);
+            }
+            for window_id in HANDLER.should_redraw() {
+                HANDLER.handle_nonuser_event(Event::WindowEvent {
+                    window_id,
+                    event: WindowEvent::RedrawRequested,
+                });
+            }
+            HANDLER.handle_nonuser_event(Event::EventsCleared);
+            HANDLER.set_in_callback(false);
         }
-        HANDLER.handle_nonuser_event(Event::EventsCleared);
         if HANDLER.should_exit() {
             let _: () = unsafe { msg_send![NSApp(), stop:nil] };
             return