Fix tasks termination for Python 3.8

See discussion here: https://bugs.python.org/issue38559

Author: JonasVautherin

examples/camera.py

@@ -16,8 +16,9 @@ async def run():
             print(f"Drone discovered with UUID: {state.uuid}")
             break
 
-    asyncio.ensure_future(print_camera_mode(drone))
-    asyncio.ensure_future(print_status(drone))
+    print_mode_task = asyncio.ensure_future(print_mode(drone))
+    print_status_task = asyncio.ensure_future(print_status(drone))
+    running_tasks = [print_mode_task, print_status_task]
 
     print("Setting mode to 'PHOTO'")
     try:
@@ -33,14 +34,20 @@ async def run():
     except CameraError as error:
         print(f"Couldn't take photo: {error._result.result}")
 
-    # Shut down the running coroutines (here 'print_camera_mode()' and
+    # Shut down the running coroutines (here 'print_mode()' and
     # 'print_status()')
+    for task in running_tasks:
+        task.cancel()
+        try:
+            await task
+        except asyncio.CancelledError:
+            pass
     await asyncio.get_event_loop().shutdown_asyncgens()
 
 
-async def print_camera_mode(drone):
-    async for camera_mode in drone.camera.mode():
-        print(f"Camera mode: {camera_mode}")
+async def print_mode(drone):
+    async for mode in drone.camera.mode():
+        print(f"Camera mode: {mode}")
 
 
 async def print_status(drone):

examples/mission.py

@@ -16,8 +16,10 @@ async def run():
             print(f"Drone discovered with UUID: {state.uuid}")
             break
 
-    asyncio.ensure_future(print_mission_progress(drone))
-    termination_task = asyncio.ensure_future(observe_is_in_air(drone))
+    print_mission_progress_task = asyncio.ensure_future(print_mission_progress(drone))
+
+    running_tasks = [print_mission_progress_task]
+    termination_task = asyncio.ensure_future(observe_is_in_air(drone, running_tasks))
 
     mission_items = []
     mission_items.append(MissionItem(47.398039859999997,
@@ -74,7 +76,7 @@ async def print_mission_progress(drone):
               f"{mission_progress.total}")
 
 
-async def observe_is_in_air(drone):
+async def observe_is_in_air(drone, running_tasks):
     """ Monitors whether the drone is flying or not and
     returns after landing """
 
@@ -85,7 +87,14 @@ async def observe_is_in_air(drone):
             was_in_air = is_in_air
 
         if was_in_air and not is_in_air:
+            for task in running_tasks:
+                task.cancel()
+                try:
+                    await task
+                except asyncio.CancelledError:
+                    pass
             await asyncio.get_event_loop().shutdown_asyncgens()
+
             return
 
 

examples/telemetry_takeoff_and_land.py

@@ -35,9 +35,11 @@ async def run():
             break
 
     # Start parallel tasks
-    asyncio.ensure_future(print_altitude(drone))
-    asyncio.ensure_future(print_flight_mode(drone))
-    termination_task = asyncio.ensure_future(observe_is_in_air(drone))
+    print_altitude_task = asyncio.ensure_future(print_altitude(drone))
+    print_flight_mode_task = asyncio.ensure_future(print_flight_mode(drone))
+
+    running_tasks = [print_altitude_task, print_flight_mode_task]
+    termination_task = asyncio.ensure_future(observe_is_in_air(drone, running_tasks))
 
     # Execute the maneuvers
     print("-- Arming")
@@ -78,7 +80,7 @@ async def print_flight_mode(drone):
             print(f"Flight mode: {flight_mode}")
 
 
-async def observe_is_in_air(drone):
+async def observe_is_in_air(drone, running_tasks):
     """ Monitors whether the drone is flying or not and
     returns after landing """
 
@@ -89,6 +91,12 @@ async def observe_is_in_air(drone):
             was_in_air = is_in_air
 
         if was_in_air and not is_in_air:
+            for task in running_tasks:
+                task.cancel()
+                try:
+                    await task
+                except asyncio.CancelledError:
+                    pass
             await asyncio.get_event_loop().shutdown_asyncgens()
             return