[C API] PyType_GetSlot() should accept static types

[vstinner]

BPO	41073
Nosy	@vstinner, @encukou, @miss-islington, @shihai1991
PRs	bpo-41073: PyType_GetSlot() could accept static types. #21395 bpo-41073: PyType_GetSlot() can now accept static types. #21931

^{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 = None
closed_at = <Date 2020-11-10.20:54:53.529>
created_at = <Date 2020-06-22.08:38:14.306>
labels = ['expert-C-API', '3.10']
title = '[C API] PyType_GetSlot() should accept static types'
updated_at = <Date 2020-11-10.22:32:37.686>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2020-11-10.22:32:37.686>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2020-11-10.20:54:53.529>
closer = 'petr.viktorin'
components = ['C API']
creation = <Date 2020-06-22.08:38:14.306>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 41073
keywords = ['patch']
message_count = 10.0
messages = ['372049', '372084', '372541', '372542', '372559', '372693', '372791', '372864', '380712', '380723']
nosy_count = 4.0
nosy_names = ['vstinner', 'petr.viktorin', 'miss-islington', 'shihai1991']
pr_nums = ['21395', '21931']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue41073'
versions = ['Python 3.10']

[vstinner]

To fix bpo-40170, I would like to modify Py_TRASHCAN_BEGIN() macro to use PyType_GetSlot() to get the deallocator function, rather than accessing directly the PyTypeObject.tp_dealloc member. The problem is that currently PyType_GetSlot() only works on heap allocated types.

Would it be possible to add support for statically allocated types to PyType_GetSlot()?

Py_TRASHCAN_BEGIN() is currently defined as:

#define Py_TRASHCAN_BEGIN(op, dealloc) \
    Py_TRASHCAN_BEGIN_CONDITION(op, \
        Py_TYPE(op)->tp_dealloc == (destructor)(dealloc))

[shihai1991]

Hi, victor. If you have much bpo need to manage, I could take a look in this week :)

[shihai1991]

historical discuss: bpo-17162

[shihai1991]

I create a PR in: https://github.com/shihai1991/cpython/pull/13/commits.
Looks like It works.

If we extend PyType_GetSlot() to accept non-heaptype, we need find a way to judge the max slot of non-heaptype.

[vstinner]

historical discuss: bpo-17162

bpo-17162 added PyType_GetSlot(), but static types were not discussed there.

[shihai1991]

bpo-17162 added PyType_GetSlot(), but static types were not discussed there.
Thanks to correct my info. I paste this bpo just Larry have mentioned the static type in PyType_GetSlot() :)

[encukou]

If we extend PyType_GetSlot() to accept non-heaptype, we need find a way to judge the max slot of non-heaptype.

Static types can have some sub-slots structs but not others. A "max slot" will not help for types that have tp_as_mapping but not tp_as_number, for example.
You'll probably need some table like typeslots.inc to record which sub-slots struct each slot belongs to.

[shihai1991]

You'll probably need some table like typeslots.inc to record which sub-slots struct each slot belongs to.

Looks like it's a good way to solve this probleam, Let me try it ;)

[miss-islington]

New changeset a13b26c by Hai Shi in branch 'master':
bpo-41073: PyType_GetSlot() can now accept static types. (GH-21931)
a13b26c