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gh-104144: Skip scheduling a done callback if a TaskGroup task completes eagerly #104140

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merged 6 commits into from
May 5, 2023
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gh-104144: Skip scheduling a done callback if a TaskGroup task completes eagerly #104140

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gh-NNNN: Skip scheduling a done callback if a TaskGroup task complete…
itamaro May 3, 2023
8d6a77e
Add NEWS entry
itamaro May 3, 2023
a125c1f
Apply review feedback to NEWS entry
itamaro May 4, 2023
dae3e06
Merge branch 'main' into taskgroups-skip-done-callback
itamaro May 5, 2023
161d0f8
revert skipping _set_task_name if name is None; fix typo in comment
itamaro May 5, 2023
2b98bd9
Merge branch 'main' into taskgroups-skip-done-callback
itamaro May 5, 2023
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10 changes: 8 additions & 2 deletions Lib/asyncio/taskgroups.py
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Original file line number Diff line number Diff line change
Expand Up @@ -164,8 +164,14 @@ def create_task(self, coro, *, name=None, context=None):
else:
task = self._loop.create_task(coro, context=context)
tasks._set_task_name(task, name)
task.add_done_callback(self._on_task_done)
self._tasks.add(task)
# optimization: Immediately call the done callback if the task is
# already done (e.g. if the coro was able to complete eagerly),
# and skip scheduling a done callback
if task.done():
self._on_task_done(task)
else:
self._tasks.add(task)
task.add_done_callback(self._on_task_done)
return task

# Since Python 3.8 Tasks propagate all exceptions correctly,
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2023-05-03-16-51-53.gh-issue-104144.653Q0P.rst
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@@ -0,0 +1 @@
Optimize :class:`asyncio.TaskGroup` when using :func:`asyncio.eager_task_factory`. Skip scheduling done callbacks when all tasks finish without blocking.
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Hmm actually the scheduling is skipped on a per task basis rather than when all tasks finish without blocking.

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I have a fix in itamaro@ac1ee82 (PR depends on gh-104251 first)