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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:
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 immediatelyawaitdrift=timer.receive() # Advances the clock by 0.5 immediately tooassertdrift==approx(timedelta(0)) # Because it could trigger exactly at the tick time# Simulates a delay in the timer trigger timeasyncio.sleep(1.5) # Advances the loop monotonic clock by 1.5 seconds immediatelyawaitdrift=timer.receive() # The timer should have triggered 0.5 seconds ago, so it doesn't even sleepassertdrift==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.
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Frequenz Channels Release Notes
Summary
This release adds support to pass
Nonevalues via channels and revamps theTimerclass to support custom policies for handling missed ticks and use the loop monotonic clock. There is also a fix for theFileWatcherwhich includes a change in behavior when reporting changes for deleted files.Upgrading
util.Timerwas replaced by a more generic implementation that allows for customizable policies to handle missed ticks.If you were using
Timerto implement timeouts, these two pieces of code should be almost equivalent:Old:
New:
They are not exactly the same because the
triggered_datetimein 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
Timeruses theasyncioloop monotonic clock and the old one used the wall clock (datetime.now()) to track time. This means that when usingasync-solipsismto test, the newTimerwill always trigger immediately regardless of the state of the wall clock. This also means that we don't need to mock the wall clock withtime-machineeither 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:
Note: Before replacing this code blindly in all uses of
Timer.timeout(), please consider using the periodic timer constructorTimer.periodic()if you need a timer that triggers reliable on a periodic fashion, as the oldTimer(andTimer.timeout()) accumulates drift, which might not be what you want.FileWatchernow 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
CREATEevent 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
FileWatcherwill only emit events when the file exists, but this doesn't work forDELETEevents (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.
FileWatcherreports 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
FileWatcheras the new interface returns aFileWatcher.Eventinstead of just the file path.New Features
util.Timerwas replaced by a more generic implementation that allows for customizable policies to handle missed ticks.Passing
Nonevalues via channels is now supported.FileWatcher.Eventwas 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).FileWatcherwill now reportDELETEevents correctly.Due to a bug, before this release
DELETEevents were only reported if the file was re-created before the event was triggered.What's Changed
__del__methods only if possible by @sahas-subramanian-frequenz in Cancel pending tasks in__del__methods only if possible #85FileWatcherDELETEevent reporting and rearrange tests by @leandro-lucarella-frequenz in FixFileWatcherDELETEevent reporting and rearrange tests #86New Contributors
Full Changelog: v0.14.0...v0.15.0
This discussion was created from the release v0.15.0.
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