Improved generator finalization

[pjeby]

BPO	1463867
Nosy	@tim-one, @Yhg1s, @pjeby
Files	genfinalize.patch: Patch for generator finalization change

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/pjeby'
closed_at = <Date 2006-04-10.17:53:22.000>
created_at = <Date 2006-04-03.22:43:11.000>
labels = ['interpreter-core']
title = 'Improved generator finalization'
updated_at = <Date 2006-04-10.17:53:22.000>
user = 'https://github.com/pjeby'

bugs.python.org fields:

activity = <Date 2006-04-10.17:53:22.000>
actor = 'pje'
assignee = 'pje'
closed = True
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2006-04-03.22:43:11.000>
creator = 'pje'
dependencies = []
files = ['7139']
hgrepos = []
issue_num = 1463867
keywords = ['patch']
message_count = 5.0
messages = ['49954', '49955', '49956', '49957', '49958']
nosy_count = 3.0
nosy_names = ['tim.peters', 'twouters', 'pje']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1463867'
versions = ['Python 2.5']

[pjeby]

This patch improves generator finalization such that
simple generators (without active try/except/finally
blocks surrounding yield statements) can have their
cycles broken.

Please check to see if this patch improves the leaks
that prompted the request for changing this. Thanks.

[tim-one]

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There's no uploaded file! You have to check the
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Please try again.

(This is a SourceForge annoyance that we can do
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[pjeby]

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Argh. Sorry. Uploaded.

[Yhg1s]

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The patch looks alright (although it could use some big
blinking comments in opcode.h and ceval.c, to make sure
PyGen_NeedsFinalizer is properly updated when new block
types are added.) The patch fixes the
test_generators_cycle.py leaker-test, but it does *not* fix
the cycles test_generators test. (Obviously after removing
the code that explicitly breaks the cycle in test_generators.)

I don't know why it doesn't clean up the test_generators
cycle. Maybe it's related to doctest, or the way doctests run.

[pjeby]

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Checked in as of r45235, w/added comment to ceval.c.

If the test that's leaking doesn't leave a generator
suspended in a 'with', try/except, or try/finally block,
then a reference is probably being held somewhere that makes
it not garbage yet. (Or perhaps it's being referenced by an
object w/a __del__ method?) Let me know what you find out.