| msg255719 - (view) |
Author: Jack O'Connor (oconnor663) * |
Date: 2015-12-02 15:37 |
| The following hangs at 100% CPU on Python 3.5, though not on Python 3.4: 1) Start an asyncio coroutine with run_until_complete(). 2) Inside the coroutine, enter an ExitStack using a with-statement. 3) Inside the with-statement, call ExitStack.enter_context() with a generator context manager. It doesn't matter what the generator yields. 4) After the enter_context() call, raise an exception. Here's an example script that does all of this and repros the hang: https://gist.github.com/oconnor663/483db2820bb5f877c9ed |
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| msg255721 - (view) |
Author: Guido van Rossum (gvanrossum) *  |
Date: 2015-12-02 16:15 |
| Interestingly, it doesn't hang when you raise a different error. There's some new code dealing with the RuntimeError coming out of a generator if it raises StopIteration (instead of returning) introduced by issue #22906. Yury, it looks like you introduced that? (The diff is this: changeset: 95932:36a8d935c322 user: Yury Selivanov <yselivanov@sprymix.com> date: Sat May 09 11:44:30 2015 -0400 summary: PEP 479: Change StopIteration handling inside generators. |
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| msg255722 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-12-02 16:30 |
| Trying to reproduce without contextstack. |
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| msg255726 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-12-02 16:59 |
| Here's a minimal test to reproduce: import reprlib def main(): if 0: yield raise RuntimeError m = main() try: m.send(None) except RuntimeError as ex: ex.__context__ = ex reprlib.repr(ex) Looks like it's a bug in reprlib. It's not related to PEP 492/479. It's also reproducible in Python 3.4 and 3.3. Nick, ExitStack does this (indirectly) 'ex.__context__ = ex' thing -- I think that's a bug of contextlib. |
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| msg255728 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-12-02 17:03 |
| Created another issue for the reprlib bug: issue 25781. It appears we don't even need a generator: import reprlib try: raise RuntimeError except RuntimeError as ex: ex.__context__ = ex reprlib.repr(ex) Closing this one with "not a bug". |
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| msg255730 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-12-02 17:12 |
| It's not even a reprlib bug: try: raise Exception except Exception as ex: ex.__context__ = ex hasattr(1, 'aa') |
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| msg255732 - (view) |
Author: Jack O'Connor (oconnor663) * |
Date: 2015-12-02 17:14 |
| Thanks for chasing this down. Yury, can you suggest a workaround? |
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| msg255733 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-12-02 17:18 |
| > Thanks for chasing this down. Yury, can you suggest a workaround? I'm not sure how to workaround this :( Hopefully we can fix this in 3.5.1. |
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| msg255748 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-12-02 18:33 |
| FWIW the bug was identified in issue 25782. I've drafted a patch to fix it, please review. |
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| msg255749 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-12-02 18:35 |
| The question is whether we should raise an exception or not: ex.__context__ = ex |
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| msg255765 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-12-02 20:00 |
| Another issue for contextlib: http://bugs.python.org/issue25786 |
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| msg255777 - (view) |
Author: Jack O'Connor (oconnor663) * |
Date: 2015-12-02 20:40 |
| Yury, can you help me understand why `hasattr("foo", "bar")` triggers the infinite loop there, but not `print("foo")`? |
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| msg255778 - (view) |
Author: Yury Selivanov (yselivanov) * |
Date: 2015-12-02 20:42 |
| > Yury, can you help me understand why `hasattr("foo", "bar")` triggers the infinite loop there, but not `print("foo")`? hasattr uses getattr under the hood. getattr raises an AttributeError, and that triggers PyErr_SetError, which has an infinite "while" loop. Instead of "hasattr" you can use anything that raises an error. |
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