Async event handlers are no longer allowed (#119)

Author: almarklein

examples/demo.py

@@ -9,16 +9,13 @@
 * Can be closed with Escape or by pressing the window close button.
 * In both cases, it should print "Close detected" exactly once.
 * Hit "f" to spend 2 seconds doing direct draws.
-* Hit "s" to async-sleep the scheduling loop for 2 seconds. Resizing
-  and closing the window still work.
 
 """
 
 import time
 
 from rendercanvas.auto import RenderCanvas, loop
 from rendercanvas.utils.cube import setup_drawing_sync
-from rendercanvas.utils.asyncs import sleep
 import rendercanvas
 
 
@@ -41,7 +38,7 @@
 
 
 @canvas.add_event_handler("*")
-async def process_event(event):
+def process_event(event):
     global cursor_index
 
     if event["event_type"] not in ["pointer_move", "before_draw", "animate"]:
@@ -59,10 +56,6 @@ async def process_event(event):
                 i += 1
                 canvas.force_draw()
             print(f"Drew {i} frames in 2s.")
-        elif event["key"] == "s":
-            print("Async sleep ... zzzz")
-            await sleep(2)
-            print("waking up")
         elif event["key"] == "c":
             # Swap cursor
             shapes = list(rendercanvas.CursorShape)

rendercanvas/_events.py

@@ -50,8 +50,6 @@ def add_handler(self, *args, order: float = 0) -> Callable:
 
         Arguments:
             callback (callable, optional): The event handler. Must accept a single event argument.
-                Can be a plain function or a coroutine function.
-                If you use async callbacks, see :ref:`async` for the limitations.
             *types (list of EventType): A list of event types.
             order (float): Set callback priority order. Callbacks with lower priorities
                 are called first. Default is 0. When an event is emitted, callbacks with
@@ -113,6 +111,10 @@ def decorator(_callback: Callable):
         return decorator(callback)
 
     def _add_handler(self, callback, order, *types):
+        if iscoroutinefunction(callback):
+            raise TypeError(
+                "Coroutines cannot be callbacks (anymore). Instead, you can use a regular callback that calls `loop.add_task(coro)`."
+            )
         if self._closed:
             return
         self.remove_handler(callback, *types)
@@ -166,7 +168,7 @@ def submit(self, event):
 
         self._pending_events.append(event)
 
-    async def flush(self):
+    def flush(self):
         """Dispatch all pending events.
 
         This should generally be left to the scheduler.
@@ -176,9 +178,9 @@ async def flush(self):
                 event = self._pending_events.popleft()
             except IndexError:
                 break
-            await self.emit(event)
+            self.emit(event)
 
-    async def emit(self, event):
+    def emit(self, event):
         """Directly emit the given event.
 
         In most cases events should be submitted, so that they are flushed
@@ -192,15 +194,12 @@ async def emit(self, event):
             if event.get("stop_propagation", False):
                 break
             with log_exception(f"Error during handling {event_type} event"):
-                if iscoroutinefunction(callback):
-                    await callback(event)
-                else:
-                    callback(event)
+                callback(event)
         # Close?
         if event_type == "close":
             self._release()
 
-    async def close(self):
+    def close(self):
         """Close the event handler.
 
         Drops all pending events, send the close event, and disables the emitter.
@@ -209,4 +208,4 @@ async def close(self):
         if not self._closed:
             self._pending_events.clear()
             self.submit({"event_type": "close"})
-            await self.flush()
+            self.flush()

rendercanvas/_loop.py

@@ -117,7 +117,7 @@ async def _loop_task(self):
                 closed_canvas_ids = set(event_emitters) - set(new_event_emitters)
                 for canvas_id in closed_canvas_ids:
                     events = event_emitters[canvas_id]
-                    await events.close()
+                    events.close()
 
                 # Keep canvases alive
                 for canvas in canvases:

rendercanvas/_scheduler.py

@@ -143,7 +143,7 @@ async def __scheduler_task(self):
             # Process events, handlers may request a draw
             if (canvas := self.get_canvas()) is None:
                 break
-            await canvas._process_events()
+            canvas._process_events()
             del canvas
 
             # Determine what to do next ...
@@ -176,7 +176,7 @@ async def __scheduler_task(self):
             if not do_draw:
                 continue
 
-            await self._events.emit({"event_type": "before_draw"})
+            self._events.emit({"event_type": "before_draw"})
 
             # Ask the canvas to draw
             if (canvas := self.get_canvas()) is None:

rendercanvas/base.py

@@ -308,8 +308,8 @@ def submit_event(self, event: dict) -> None:
 
     # %% Scheduling and drawing
 
-    async def _process_events(self):
-        """Process events and animations (async).
+    def _process_events(self):
+        """Process events and animations.
 
         Called from the scheduler.
         """
@@ -323,7 +323,7 @@ async def _process_events(self):
 
         # Flush our events, so downstream code can update stuff.
         # Maybe that downstream code request a new draw.
-        await self._events.flush()
+        self._events.flush()
 
         # TODO: implement later (this is a start but is not tested)
         # Schedule animation events until the lag is gone

rendercanvas/stub.py

@@ -70,8 +70,8 @@ class StubRenderCanvas(BaseRenderCanvas):
     def _final_canvas_init(self):
         return super()._final_canvas_init()
 
-    async def _process_events(self):
-        return await super()._process_events()
+    def _process_events(self):
+        return super()._process_events()
 
     def _draw_frame_and_present(self):
         return super()._draw_frame_and_present()

tests/test_base.py

@@ -198,15 +198,7 @@ def handler(event):
     c.submit_event({"event_type": "key_down", "value": 1})
     c.submit_event({"event_type": "key_down", "value": 2})
 
-    def sync_flush(events):
-        coro = events.flush()
-        while True:
-            try:
-                coro.send(None)
-            except StopIteration:
-                break
-
-    sync_flush(c._events)
+    c._events.flush()
     assert events == [1, 2]