API function PySignal_SetWakeupFd is not exported and unusable

[cy]

BPO	45201
Nosy	@vstinner

^{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 2021-09-15.06:03:15.175>
labels = ['expert-C-API', 'type-bug', '3.9']
title = 'API function PySignal_SetWakeupFd is not exported and unusable'
updated_at = <Date 2021-09-29.08:18:20.534>
user = 'https://bugs.python.org/cy'

bugs.python.org fields:

activity = <Date 2021-09-29.08:18:20.534>
actor = 'vstinner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2021-09-15.06:03:15.175>
creator = 'cy'
dependencies = []
files = []
hgrepos = []
issue_num = 45201
keywords = []
message_count = 2.0
messages = ['401810', '402828']
nosy_count = 2.0
nosy_names = ['vstinner', 'cy']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue45201'
versions = ['Python 3.9']

[cy]

I want to wait on curl_multi_wait which messes up python's signal handling since libcurl doesn't know to exit the polling loop on signal. I created a pipe that curl could read from when python registered a signal, and PySignal_SetWakeupFd would write to the pipe, thus letting curl leave its polling loop, letting my C module return an exception condition.

Except PySignal_SetWakeupFd cannot be used.

In Modules/signalmodule.c, it says:

    int
    PySignal_SetWakeupFd(int fd)

when it should say:

    PyAPI_FUNC(int)
    PySignal_SetWakeupFd(int fd)

This probably isn't a problem for most, since gcc has visiblity=public by default, but I guess Gentoo's process for building python sets -fvisibility=hidden, so I can't access it, and all Microsoft users should have no access to PySignal_SetWakeupFd, since Microsoft does have hidden visibility by default.

[vstinner]

See also bpo-45316: [C API] Functions not exported with PyAPI_FUNC().