v0.15.0

Frequenz Channels Release Notes

Summary

This release adds support to pass None values via channels and revamps the Timer class to support custom policies for handling missed ticks and use the loop monotonic clock. There is also a fix for the FileWatcher which includes a change in behavior when reporting changes for deleted files.

Upgrading

• util.Timer was replaced by a more generic implementation that allows for customizable policies to handle missed ticks.

  If you were using Timer to implement timeouts, these two pieces of code should be almost equivalent:

  • Old:

    old_timer = Timer(1.0)
    triggered_datetime = old_timer.receive()

  • New:

    new_timer = Timer.timeout(timedelta(seconds=1.0))
    drift = new_timer.receive()
    triggered_datetime = datetime.now(timezone.utc) - drift

  They are not exactly the same because the triggered_datetime in the second case will not be exactly when the timer had triggered, but that shouldn't be relevant, the important part is when your code can actually react to the timer trigger and to know how much drift there was to be able to take corrective actions.

  Also the new Timer uses the asyncio loop monotonic clock and the old one used the wall clock (datetime.now()) to track time. This means that when using async-solipsism to test, the new Timer will always trigger immediately regardless of the state of the wall clock. This also means that we don't need to mock the wall clock with time-machine either now.

  With the previous timer one needed to create a separate task to run the timer, because otherwise it would block as it loops until the wall clock was at a specific time. Now the code will run like this:

  timer = Timer.timeout(timedelta(seconds=1.0))
  asyncio.sleep(0.5)  # Advances the loop monotonic clock by 0.5 seconds immediately
  await drift = timer.receive()  # Advances the clock by 0.5 immediately too
  assert drift == approx(timedelta(0))  # Because it could trigger exactly at the tick time
  
  # Simulates a delay in the timer trigger time
  asyncio.sleep(1.5)  # Advances the loop monotonic clock by 1.5 seconds immediately
  await drift = timer.receive()  # The timer should have triggered 0.5 seconds ago, so it doesn't even sleep
  assert drift == approx(timedelta(seconds=0.5))  # Now we should observe a drift of 0.5 seconds

  Note: Before replacing this code blindly in all uses of Timer.timeout(), please consider using the periodic timer constructor Timer.periodic() if you need a timer that triggers reliable on a periodic fashion, as the old Timer (and Timer.timeout()) accumulates drift, which might not be what you want.

• FileWatcher now will emit events even if the file doesn't exist anymore.

  Because the underlying library has a considerable delay in triggering filesystem events, it can happen that, for example, a CREATE event is received but at the time of receiving the file doesn't exist anymore (because if was removed just after creation and before the event was triggered).

  Before the FileWatcher will only emit events when the file exists, but this doesn't work for DELETE events (clearly). Given the nature of this mechanism can lead to races easily, it is better to leave it to the user to decide when these situations happen and just report all events.

  Therefore, you should now check a file receiving an event really exist before trying to operate on it.

• FileWatcher reports the type of event observed in addition to the file path.

  Previously, only the file path was reported. With this update, users can now determine if a file change is a creation, modification, or deletion.
  Note that this change may require updates to your existing code that relies on FileWatcher as the new interface returns a FileWatcher.Event instead of just the file path.

New Features

• util.Timer was replaced by a more generic implementation that allows for customizable policies to handle missed ticks.

• Passing None values via channels is now supported.

• FileWatcher.Event was added to notify events when a file is created, modified, or deleted.

Bug Fixes

• util.Select / util.Merge / util.MergeNamed: Cancel pending tasks in __del__ methods only if possible (the loop is not already closed).

• FileWatcher will now report DELETE events correctly.

  Due to a bug, before this release DELETE events were only reported if the file was re-created before the event was triggered.

What's Changed

• Clear release notes by @leandro-lucarella-frequenz in #81
• Publish to PyPi using trusted publishing by @leandro-lucarella-frequenz in #84
• Add support/tests for None-value channels by @sahas-subramanian-frequenz in #83
• Cancel pending tasks in __del__ methods only if possible by @sahas-subramanian-frequenz in #85
• Make the timer generic and support periodic timers by @leandro-lucarella-frequenz in #79
• Fix FileWatcher DELETE event reporting and rearrange tests by @leandro-lucarella-frequenz in #86
• Report the type of change observed in FileWatcher by @daniel-zullo-frequenz in #87

New Contributors

• @sahas-subramanian-frequenz made their first contribution in #83
• @daniel-zullo-frequenz made their first contribution in #87

Full Changelog: v0.14.0...v0.15.0