Fix timer reset() while it is being waited on (#241)

If the timer was reset while it was being waited on, the next tick time
was not recalculated and the timer would wait for the original time
instead of the new one.

This means a timeout could fire even if there was actually no timeout
(because the timer was reset).

Author: llucax

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