Timer: Make stop() and reset() interrupt a waiting timer

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

RELEASE_NOTES.md

@@ -3,3 +3,5 @@
 ## Bug Fixes
 
 - `FileWatcher`: Fixed `ready()` method to return False when an error occurs. Before this fix, `select()` (and other code using `ready()`) never detected the `FileWatcher` was stopped and the `select()` loop was continuously waking up to inform the receiver was ready.
+
+- `Timer.stop()` and `Timer.reset()` now immediately stop the timer if it is running. Before this fix, the timer would continue to run until the next interval.

src/frequenz/channels/timer.py

@@ -523,6 +523,8 @@ def __init__(  # pylint: disable=too-many-arguments
         See the documentation of `MissedTickPolicy` for details.
         """
 
+        self._reset_event = asyncio.Event()
+
         self._loop: asyncio.AbstractEventLoop = (
             loop if loop is not None else asyncio.get_running_loop()
         )
@@ -605,7 +607,13 @@ def reset(self, *, start_delay: timedelta = timedelta(0)) -> None:
         if start_delay_ms < 0:
             raise ValueError(f"`start_delay` can't be negative, got {start_delay}")
         self._stopped = False
+
+        prev_next_tick_time = self._next_tick_time
         self._next_tick_time = self._now() + start_delay_ms + self._interval
+
+        if prev_next_tick_time and prev_next_tick_time > self._next_tick_time:
+            self._reset_event.set()
+
         self._current_drift = None
 
     def stop(self) -> None:
@@ -621,6 +629,7 @@ def stop(self) -> None:
         self._stopped = True
         # We need to make sure it's not None, otherwise `ready()` will start it
         self._next_tick_time = self._now()
+        self._reset_event.set()
 
     # We need a noqa here because the docs have a Raises section but the documented
     # exceptions are raised indirectly.
@@ -664,7 +673,12 @@ async def ready(self) -> bool:  # noqa: DOC502
         # could be reset while we are sleeping, in which case we need to recalculate
         # the time to the next tick and try again.
         while time_to_next_tick > 0:
-            await asyncio.sleep(time_to_next_tick / 1_000_000)
+            for fin in asyncio.as_completed(
+                [asyncio.sleep(time_to_next_tick / 1_000_000), self._reset_event.wait()]
+            ):
+                await fin
+                break
+            self._reset_event.clear()
             now = self._now()
             time_to_next_tick = self._next_tick_time - now