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bpo-44263: Better explain the GC contract for PyType_FromSpecWithBases#26442

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pablogsal merged 1 commit intopython:mainfrom
pablogsal:gc_docs
May 29, 2021
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bpo-44263: Better explain the GC contract for PyType_FromSpecWithBases#26442
pablogsal merged 1 commit intopython:mainfrom
pablogsal:gc_docs

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@pablogsal pablogsal commented May 29, 2021 •
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@bedevere-bot bedevere-bot added awaiting core review docs Documentation in the Doc dir labels May 29, 2021
@pablogsal pablogsal requested review from encukou and vstinner and removed request for encukou May 29, 2021 00:01
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pablogsal commented May 29, 2021

CC: @erlend-aasland

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Thanks for the clarifications. I was pretty confused with your fix at 8b4312b. So I'm glad the reason is in the docs now!

If I'm understanding correctly, in that specific case, you want _ssl.SSLError to inherit its tp_traverse etc. fields from the parent PyExc_OSError (which implements the GC), so you didn't set Py_TPFLAGS_HAVE_GC in _ssl.SSLError?

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pablogsal commented May 29, 2021

If I'm understanding correctly, in that specific case, you want _ssl.SSLError to inherit its tp_traverse etc. fields from the parent PyExc_OSError (which implements the GC), so you didn't set Py_TPFLAGS_HAVE_GC in _ssl.SSLError?

Correct, this is because SSLError doesn't add any extra fields: is just PyOSErrorObject.

@pablogsal pablogsal merged commit 8b55bc3 into python:main May 29, 2021
@pablogsal pablogsal deleted the gc_docs branch May 29, 2021 02:57
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miss-islington commented May 29, 2021

Thanks @pablogsal for the PR 🌮🎉.. I'm working now to backport this PR to: 3.10, 3.9.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

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bedevere-bot commented May 29, 2021

GH-26443 is a backport of this pull request to the 3.10 branch.

@bedevere-bot bedevere-bot removed the needs backport to 3.10 only security fixes label May 29, 2021
miss-islington pushed a commit to miss-islington/cpython that referenced this pull request May 29, 2021
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bpo-44263: Better explain the GC contract for PyType_FromSpecWithBases (
9b57aad 
pythonGH-26442)

(cherry picked from commit 8b55bc3)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
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bedevere-bot commented May 29, 2021

GH-26444 is a backport of this pull request to the 3.9 branch.

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request May 29, 2021
@pablogsal @miss-islington
bpo-44263: Better explain the GC contract for PyType_FromSpecWithBases (
0974c96 
pythonGH-26442)

(cherry picked from commit 8b55bc3)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
miss-islington added a commit that referenced this pull request May 29, 2021
@miss-islington @pablogsal
bpo-44263: Better explain the GC contract for PyType_FromSpecWithBases (
a30cbae 
GH-26442)

(cherry picked from commit 8b55bc3)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
pablogsal added a commit that referenced this pull request May 29, 2021
@miss-islington @pablogsal
bpo-44263: Better explain the GC contract for PyType_FromSpecWithBases (
11049be 
GH-26442) (GH-26443)

(cherry picked from commit 8b55bc3)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
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encukou commented Jun 1, 2021

Thank you for the clarification!

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vstinner commented Jun 1, 2021

Thank you for the clarification!

Yeah, thanks Pablo! This part wasn't obvious to me at all, especially the type inheritance part.

FYI Pablo and me hit this issue the hard way while debugging a random crash involving the _ssl.SSLError exception: https://bugs.python.org/issue44252 Two unit tests only crashed on Windows, and only if you ran the unit test in a very specific way. GC collections are not really "determistic" from my human debugger pointer of view :-) I made the crash more likely by running import gc; gc.set_threshold(5) at Python startup.

@pablogsal pablogsal mentioned this pull request Jul 18, 2021
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@pablogsal pablogsal mentioned this pull request May 2, 2022
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