Hi folks,
I wanted to raise visibility about a few asyncio PR's I'm hoping can be
merged before the 3.9 beta deadline -- which is ~10 days away. The four
PR's are listed at the end of this message.
The PR's are on the simple side compared to others. I think collectively
they can make asyncio a lot easier to use and troubleshoot. This is because
they address various situations where parts of the traceback or stacktrace
can go missing in asyncio, which makes issues a lot harder to pin down.
The issue of incomplete tracebacks was probably the biggest pain point for
me when I was starting out with asyncio. Like, here's an email I sent to
this list two and a half years ago:
https://mail.python.org/pipermail/async-sig/2017-November/000403.html
Below are the four issues, in the order in which I think they should be
reviewed (in order of both simplicity and impact, in my estimation):
1) bpo-29587: Enable exception chaining for gen.throw() with "yield from":
https://github.com/python/cpython/pull/19858
This PR addresses a third example of the following bpo issue (not one of
the two listed by Nathaniel, but with the same root cause as the others):
https://bugs.python.org/issue29587
This aspect causes parts of the traceback to go missing / be swallowed in
certain situations if an exception happens while awaiting an async task.
2) bpo-31033: Full tracebacks for cancelled asyncio tasks:
https://github.com/python/cpython/pull/19951
This is a big one because currently, the traceback for cancelled tasks
shows almost nothing. This PR would show a traceback starting with what
code got interrupted, and how the exception bubbled up from there.
It's one aspect of the following issue about making cancelled tasks easier
to diagnose:
https://bugs.python.org/issue31033
3) bpo-29590: fix stack trace for gen.throw() with yield from
https://github.com/python/cpython/pull/19896
This is a second issue that Nathaniel filed:
https://bugs.python.org/issue29590
It's about how stack trace entries get lost if you're trying to profile
asyncio code.
4) bpo-31033: Add a msg argument to Future.cancel() and Task.cancel()
https://github.com/python/cpython/pull/19979
This PR would let you pass a "msg" to cancel(), which would show up in the
traceback as the CancelledError's message. This is the other side of #2
(bpo-31033) because it would let you record _why_ a task was cancelled, or
other details (as opposed to seeing _what_ got cancelled).
Thank you,
--Chris
