Advanced Debugger Support C-API is useless without HEAD_LOCK()/HEAD_UNLOCK()

[AndreiPashkin]

BPO	41062
Nosy	@vstinner, @AndreiPashkin

^{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 = None
created_at = <Date 2020-06-21.08:53:48.034>
labels = ['expert-C-API', 'type-feature', '3.11']
title = 'Advanced Debugger Support C-API is useless without HEAD_LOCK()/HEAD_UNLOCK()'
updated_at = <Date 2021-12-06.18:25:56.506>
user = 'https://github.com/AndreiPashkin'

bugs.python.org fields:

activity = <Date 2021-12-06.18:25:56.506>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2020-06-21.08:53:48.034>
creator = 'pashkin'
dependencies = []
files = []
hgrepos = []
issue_num = 41062
keywords = []
message_count = 2.0
messages = ['371988', '371989']
nosy_count = 2.0
nosy_names = ['vstinner', 'pashkin']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue41062'
versions = ['Python 3.11']

[AndreiPashkin]

To me it seems like Advanced Debugger Support C-API doesn't make sense without HEAD_LOCK() and HEAD_UNLOCK() which are private right now.

When researching how C-API works I've found this comment in the source code:

cpython/Python/pystate.c

Line 1176 in e838a93

* Because these lists can mutate even when the GIL is held, we

It says that the lists of interpreter-state and thread-state objects (that Adv. Debugger Support API operates on) could be mutated even when GIL is held so there is need to acquire head mutex when accessing them. But there is no way to acquire head mutex using public C-API.

Am I right? If yes - it seems like HEAD_(UN)LOCK() should be made public.

[AndreiPashkin]

Here is what I mean by "Advanced Debugger Support" API:
https://docs.python.org/dev/c-api/init.html#advanced-debugger-support