Fix timer reset() while it is being waited on

RELEASE_NOTES.md

@@ -145,4 +145,4 @@
 
 ## Bug Fixes
 
-<!-- Here goes notable bug fixes that are worth a special mention or explanation -->
+* `Timer`: Fix bug that was causing calls to `reset()` to not reset the timer, if the timer was already being awaited.

src/frequenz/channels/timer.py

@@ -696,10 +696,15 @@ async def ready(self) -> bool:  # noqa: DOC502
 
         now = self._now()
         time_to_next_tick = self._next_tick_time - now
+
         # If we didn't reach the tick yet, sleep until we do.
-        if time_to_next_tick > 0:
+        # We need to do this in a loop also reacting to the reset event, as the timer
+        # could be reset while we are sleeping, in which case we need to recalculated
+        # 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)
             now = self._now()
+            time_to_next_tick = self._next_tick_time - now
 
         # If a stop was explicitly requested during the sleep, we bail out.
         if self._stopped:

tests/test_timer_integration.py

@@ -0,0 +1,34 @@
+# License: MIT
+# Copyright © 2023 Frequenz Energy-as-a-Service GmbH
+
+"""Integration tests for the timer."""
+
+
+import asyncio
+from datetime import timedelta
+
+import async_solipsism
+import pytest
+
+from frequenz.channels.timer import Timer
+
+
+@pytest.mark.integration
+async def test_timer_timeout_reset(
+    event_loop: async_solipsism.EventLoop,  # pylint: disable=redefined-outer-name
+) -> None:
+    """Test that the receiving is properly adjusted after a reset."""
+
+    async def timer_wait(timer: Timer) -> None:
+        await timer.receive()
+
+    async with asyncio.timeout(2.0):
+        async with asyncio.TaskGroup() as task_group:
+            timer = Timer.timeout(timedelta(seconds=1.0))
+            start_time = event_loop.time()
+            task_group.create_task(timer_wait(timer))
+            await asyncio.sleep(0.5)
+            timer.reset()
+
+    run_time = event_loop.time() - start_time
+    assert run_time >= 1.5