asyncio: Add support to close the running loop and cancel background tasks #15715
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This allows to collect all running tasks either for inspection and debugging, or to cancel them all. Signed-off-by: Jared Hancock <jared.hancock@centeredsolutions.com>
This matches the way CPython works. If the main task finishes or raises an exception, the background tasks are all considered to be daemon tasks and are canceled and the loop is shutdown. Signed-off-by: Jared Hancock <jared.hancock@centeredsolutions.com>
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## master #15715 +/- ##
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+ Coverage 98.43% 98.44% +0.01%
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Files 163 163
Lines 21290 21304 +14
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+ Hits 20956 20972 +16
+ Misses 334 332 -2 ☔ View full report in Codecov by Sentry. |
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Summary
CPython will automatically shutdown the event loop and cancel all background async tasks when the main task exits from
asyncio.run(...). This is especially important if the background tasks need to perform some sort of cleanup and/or reset.This adds support for
asyncio.all_tasks()which returns asetobject similar to the way CPython works and allows inspection of all running tasks. This may be used inside a running event loop to forcibly cancel all running tasks.Testing
This adds two tests in hopes of measuring compatibility with CPython. The first is
asyncio_all_taskswhich shows the collection of tasks returned from theasyncio.all_tasks()function. The second isasyncio_shutdownwhich shows the compatibility of shutting down background tasks as the main task exits for various reasons.Trade-offs and Alternatives
The spirit of this feature was originally implemented in #9870; however, it needs this concept to fully work correctly.
Micropython still suffers from the issue where a
tryblock in the main task will not have itsfinallyexecuted if it's interrupted from a KeyboardInterrupted (like eg. frommpremote); however, at least this will trigger the proper cancel and cleanup of background tasks.As a caveat the
Loopin Micropython can be reused after being close()d. In CPython, such is forbidden. CPython uses aRunnerto manage the shutdown of the loop and tasks after the main task exits.