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Refactor asyncio.wait_for() #31847

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Refactor asyncio.wait_for() #31847

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80590ab
Implement wait_for on top on timeout() and TaskGroup()
asvetlov Mar 13, 2022
5e25891
TaskGroup is not required here
asvetlov Mar 13, 2022
b196632
Merge branch 'main' into refactor-wait_for
asvetlov Mar 16, 2022
a700725
Cancel the inner task
asvetlov Mar 16, 2022
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59 changes: 5 additions & 54 deletions Lib/asyncio/tasks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@
from . import events
from . import exceptions
from . import futures
from . import timeouts
from .coroutines import _is_coroutine

# Helper to generate new task names
Expand Down Expand Up @@ -442,62 +443,12 @@ async def wait_for(fut, timeout):

This function is a coroutine.
"""
loop = events.get_running_loop()

if timeout is None:
return await fut

if timeout <= 0:
fut = ensure_future(fut, loop=loop)

if fut.done():
return fut.result()

await _cancel_and_wait(fut, loop=loop)
try:
return fut.result()
except exceptions.CancelledError as exc:
raise exceptions.TimeoutError() from exc

waiter = loop.create_future()
timeout_handle = loop.call_later(timeout, _release_waiter, waiter)
cb = functools.partial(_release_waiter, waiter)

fut = ensure_future(fut, loop=loop)
fut.add_done_callback(cb)
async def inner():
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@graingert graingert Jul 20, 2022 •
edited
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@asvetlov I've been having a go at this branch in bf594bd

you need to special case None in asyncio.wait_for(

Suggested change
async def inner():
if timeout is None:
return await fut
async def inner():

and then special case 0 in timeouts.timeout see https://gist.github.com/graingert/ea2546b23b32be5a4493a9a115db2eff#file-timeout_bug-py-L6

async with timeouts.timeout(timeout):
return await fut

try:
# wait until the future completes or the timeout
try:
await waiter
except exceptions.CancelledError:
if fut.done():
return fut.result()
else:
fut.remove_done_callback(cb)
# We must ensure that the task is not running
# after wait_for() returns.
# See https://bugs.python.org/issue32751
await _cancel_and_wait(fut, loop=loop)
raise

if fut.done():
return fut.result()
else:
fut.remove_done_callback(cb)
# We must ensure that the task is not running
# after wait_for() returns.
# See https://bugs.python.org/issue32751
await _cancel_and_wait(fut, loop=loop)
# In case task cancellation failed with some
# exception, we should re-raise it
# See https://bugs.python.org/issue40607
try:
return fut.result()
except exceptions.CancelledError as exc:
raise exceptions.TimeoutError() from exc
finally:
timeout_handle.cancel()
return await create_task(inner())
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@graingert graingert Jul 21, 2022 •
edited
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I don't think this extra create_task is worth it, the tests it passes are equivalent to:

async def wait_for(fut, delay):
    if delay is None:
        return await fut
    if delay <= 0:
        if asyncio.iscoroutine(fut):
            fut.close()
            raise TimeoutError

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I think it would be better to skip this create_task and delete the tests that fail



async def _wait(fs, timeout, return_when, loop):
Expand Down