[issue21886] asyncio: Future.set_result() called on cancelled Future raises asyncio.futures.InvalidStateError

2014-07-05 Thread STINNER Victor 

STINNER Victor added the comment:

Fix commited to Tulip (4655ef2d9f43), Python 3.4 and 3.5.

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[issue21886] asyncio: Future.set_result() called on cancelled Future raises asyncio.futures.InvalidStateError

2014-07-05 Thread Roundup Robot 

Roundup Robot added the comment:

New changeset d7e4efd5e279 by Victor Stinner in branch '3.4':
Closes #21886, #21447: Fix a race condition in asyncio when setting the result
http://hg.python.org/cpython/rev/d7e4efd5e279

New changeset 50c995bdc00a by Victor Stinner in branch 'default':
(Merge 3.4) Closes #21886, #21447: Fix a race condition in asyncio when setting
http://hg.python.org/cpython/rev/50c995bdc00a

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nosy: +python-dev
resolution:  - fixed
stage:  - resolved
status: open - closed

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[issue21886] asyncio: Future.set_result() called on cancelled Future raises asyncio.futures.InvalidStateError

2014-06-30 Thread STINNER Victor 

New submission from STINNER Victor:

Ok, I found a way to reproduce the error InvalidStateError in asyncio. I'm not 
sure that it's the same the error in #21447.

Output of attached bug.py in debug mode:
---
Exception in callback Future.set_result(None)
handle: TimerHandle when=79580.878306285 Future.set_result(None)
source_traceback: Object created at (most recent call last):
  File /home/haypo/bug.py, line 11, in module
loop.run_until_complete(task2)
  File /home/haypo/prog/python/default/Lib/asyncio/base_events.py, line 239, 
in run_until_complete
self.run_forever()
  File /home/haypo/prog/python/default/Lib/asyncio/base_events.py, line 212, 
in run_forever
self._run_once()
  File /home/haypo/prog/python/default/Lib/asyncio/base_events.py, line 912, 
in _run_once
handle._run()
  File /home/haypo/prog/python/default/Lib/asyncio/events.py, line 96, in _run
self._callback(*self._args)
  File /home/haypo/prog/python/default/Lib/asyncio/tasks.py, line 241, in 
_step
result = next(coro)
  File /home/haypo/prog/python/default/Lib/asyncio/coroutines.py, line 72, in 
__next__
return next(self.gen)
  File /home/haypo/prog/python/default/Lib/asyncio/tasks.py, line 487, in 
sleep
h = future._loop.call_later(delay, future.set_result, result)
Traceback (most recent call last):
  File /home/haypo/prog/python/default/Lib/asyncio/events.py, line 96, in _run
self._callback(*self._args)
  File /home/haypo/prog/python/default/Lib/asyncio/futures.py, line 326, in 
set_result
raise InvalidStateError('{}: {!r}'.format(self._state, self))
asyncio.futures.InvalidStateError: CANCELLED: Future cancelled
---

The fix is to replace the following line of sleep():
---
h = future._loop.call_later(delay, future.set_result, result)
---

with:
---
def maybe_set_result(future, result):
if not future.cancelled():
future.set_result(result)
h = future._loop.call_later(delay, maybe_set_result, future, result)
---

This generic issue was already discussed there:
https://groups.google.com/forum/?fromgroups#!searchin/python-tulip/set_result$20InvalidStateError/python-tulip/T1sxLqjuoVY/YghF-YsgosgJ

A patch was also proposed:
https://codereview.appspot.com/69870048/

--
files: bug.py
messages: 221961
nosy: haypo
priority: normal
severity: normal
status: open
title: asyncio: Future.set_result() called on cancelled Future raises 
asyncio.futures.InvalidStateError
versions: Python 3.5
Added file: http://bugs.python.org/file35807/bug.py

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[issue21886] asyncio: Future.set_result() called on cancelled Future raises asyncio.futures.InvalidStateError

2014-06-30 Thread Ryder Lewis 

Changes by Ryder Lewis rle...@softgatesystems.com:


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[issue21886] asyncio: Future.set_result() called on cancelled Future raises asyncio.futures.InvalidStateError

2014-06-30 Thread STINNER Victor 

STINNER Victor added the comment:

I see two options to fix this issue:

- add an optional parameter to set_result() to do nothing if the future is 
cancelled
- add a method (public or private) to set a result or do nothing if the future 
is cancelled

Patch Add ignore_cancelled and ignore_done to Future.set_result() (for Tulip):
http://codereview.appspot.com/109340043

Patch Add Future._maybe_set_result():
http://codereview.appspot.com/108300043

I prefer the second patch because it doesn't touch the public API and it is 
shorter.

Note: the first patch contains unrelated changes, like checking fut.cancelled() 
instead of fut.done().

_maybe_set_result() is not a good name. Other suggestions: 
_set_result_except_cancelled, _set_result_ignore_cancelled.

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[issue21886] asyncio: Future.set_result() called on cancelled Future raises asyncio.futures.InvalidStateError

2014-06-30 Thread STINNER Victor 

STINNER Victor added the comment:

In https://codereview.appspot.com/69870048/ Guido proposed to test to replace:
   self._loop.call_soon(waiter.set_result, None)
with:
   if not waiter.cancelled():
  waiter.set_result(None)

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[issue21886] asyncio: Future.set_result() called on cancelled Future raises asyncio.futures.InvalidStateError

2014-06-30 Thread STINNER Victor 

STINNER Victor added the comment:

 _maybe_set_result() is not a good name. Other suggestions: 
 _set_result_except_cancelled, _set_result_ignore_cancelled.

I read again the mail thread and Guido proposed the nice name 
_set_result_unless_cancelled() which is very explicit. I updated my patch:
http://codereview.appspot.com/108300043

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