Allow concurrent buffering and dispatch of input events

main/input_default.cpp

@@ -36,6 +36,10 @@
 #include "scene/resources/texture.h"
 #include "servers/visual_server.h"
 
+#ifdef DEV_ENABLED
+#include "core/os/thread.h"
+#endif
+
 void InputDefault::SpeedTrack::update(const Vector2 &p_delta_p) {
 	uint64_t tick = OS::get_singleton()->get_ticks_usec();
 	uint32_t tdiff = tick - last_tick;
@@ -311,6 +315,10 @@ Vector3 InputDefault::get_gyroscope() const {
 }
 
 void InputDefault::_parse_input_event_impl(const Ref<InputEvent> &p_event, bool p_is_emulated) {
+	// This function does the final delivery of the input event to user land.
+	// Regardless where the event came from originally, this has to happen on the main thread.
+	DEV_ASSERT(Thread::get_caller_id() == Thread::get_main_id());
+
 	// Notes on mouse-touch emulation:
 	// - Emulated mouse events are parsed, that is, re-routed to this method, so they make the same effects
 	//   as true mouse events. The only difference is the situation is flagged as emulated so they are not
@@ -354,7 +362,9 @@ void InputDefault::_parse_input_event_impl(const Ref<InputEvent> &p_event, bool
 			touch_event->set_pressed(mb->is_pressed());
 			touch_event->set_position(mb->get_position());
 			touch_event->set_double_tap(mb->is_doubleclick());
+			_THREAD_SAFE_UNLOCK_
 			main_loop->input_event(touch_event);
+			_THREAD_SAFE_LOCK_
 		}
 	}
 
@@ -376,7 +386,9 @@ void InputDefault::_parse_input_event_impl(const Ref<InputEvent> &p_event, bool
 			drag_event->set_relative(relative);
 			drag_event->set_speed(get_last_mouse_speed());
 
+			_THREAD_SAFE_UNLOCK_
 			main_loop->input_event(drag_event);
+			_THREAD_SAFE_LOCK_
 		}
 	}
 
@@ -472,7 +484,9 @@ void InputDefault::_parse_input_event_impl(const Ref<InputEvent> &p_event, bool
 
 	if (ge.is_valid()) {
 		if (main_loop) {
+			_THREAD_SAFE_UNLOCK_
 			main_loop->input_event(ge);
+			_THREAD_SAFE_LOCK_
 		}
 	}
 
@@ -495,7 +509,9 @@ void InputDefault::_parse_input_event_impl(const Ref<InputEvent> &p_event, bool
 	}
 
 	if (main_loop) {
+		_THREAD_SAFE_UNLOCK_
 		main_loop->input_event(p_event);
+		_THREAD_SAFE_LOCK_
 	}
 }
 
@@ -747,8 +763,15 @@ void InputDefault::flush_buffered_events() {
 	_THREAD_SAFE_METHOD_
 
 	while (buffered_events.front()) {
-		_parse_input_event_impl(buffered_events.front()->get(), false);
+		// The final delivery of the input event involves releasing the lock.
+		// While the lock is released, another thread may lock it and add new events to the back.
+		// Therefore, we get each event and pop it while we still have the lock,
+		// to ensure the list is in a consistent state.
+		List<Ref<InputEvent>>::Element *E = buffered_events.front();
+		Ref<InputEvent> e = E->get();
 		buffered_events.pop_front();
+
+		_parse_input_event_impl(e, false);
 	}
 }