Timer: Add support for rearming timer with new interval

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

Author: Marenz

RELEASE_NOTES.md

@@ -1,5 +1,9 @@
 # Frequenz channels Release Notes
 
+## New Features
+
+- `Timer.reset()` now supports setting the interval and will restart the timer with the new interval.
+
 ## 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.

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()
         )
@@ -584,7 +586,12 @@ def is_running(self) -> bool:
         """Whether the timer is running."""
         return not self._stopped
 
-    def reset(self, *, start_delay: timedelta = timedelta(0)) -> None:
+    def reset(
+        self,
+        *,
+        interval: timedelta | None = None,
+        start_delay: timedelta = timedelta(0),
+    ) -> None:
         """Reset the timer to start timing from now (plus an optional delay).
 
         If the timer was stopped, or not started yet, it will be started.
@@ -593,6 +600,8 @@ def reset(self, *, start_delay: timedelta = timedelta(0)) -> None:
         more details.
 
         Args:
+            interval: The new interval between ticks. If `None`, the current
+                interval is kept.
             start_delay: The delay before the timer should start. This has microseconds
                 resolution, anything smaller than a microsecond means no delay.
 
@@ -605,7 +614,16 @@ 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
+
+        if interval is not None:
+            self._interval = _to_microseconds(interval)
+
+        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:
@@ -664,7 +682,13 @@ 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)
+            await asyncio.wait(
+                [
+                    asyncio.create_task(asyncio.sleep(time_to_next_tick / 1_000_000)),
+                    asyncio.create_task(self._reset_event.wait()),
+                ],
+                return_when=asyncio.FIRST_COMPLETED,
+            )
             now = self._now()
             time_to_next_tick = self._next_tick_time - now