PyEval_ReInitThreads() is used internally by PyOS_AfterFork_Child(). I don't see the point of calling it directly. If you care of threads after fork, just call PyOS_AfterFork_Child(), no?

I propose to remove PyEval_ReInitThreads() from the public C API.

Problem: it's documented as a public function in High-level API of the Python Initialization API:
https://docs.python.org/dev/c-api/init.html#c.PyEval_ReInitThreads

On the Internet, I found a single project calling directly this function, but it's only in a test used to the test Python threading API:
https://github.com/DataDog/go-python3/blob/master/thread_test.go


func TestThreadInitialization(t *testing.T) {
	Py_Initialize()
	PyEval_InitThreads()

	assert.True(t, PyEval_ThreadsInitialized())

	PyEval_ReInitThreads()
}

I don't think that the PyEval_ReInitThreads() call here makes any sense.

The function was added 19 years ago:

commit fee3a2dd8cf984b8261032086fe513bf7327b601
Author: Guido van Rossum <guido@python.org>
Date:   Sun Aug 27 17:34:07 2000 +0000

    Charles Waldman's patch to reinitialize the interpreter lock after a
    fork.  This solves the test_fork1 problem.  (ceval.c, signalmodule.c,
    intrcheck.c)
    
    SourceForge: [ Patch #101226 ] make threading fork-safe

fwiw - i agree that this can be removed.  it has no reason to ever be called directly.  i double checked in our massive internal codebase at work and found no calls other than python interpreters themselves.

> i double checked in our massive internal codebase at work and found no calls other than python interpreters themselves.

Thanks. It confirms what I understood using GitHub code search (see my initial message).

New changeset d5d9e81ce9a7efc5bc14a5c21398d1ef6f626884 by Victor Stinner in branch 'master':
bpo-36728: Remove PyEval_ReInitThreads() from C API (GH-13241)
https://github.com/python/cpython/commit/d5d9e81ce9a7efc5bc14a5c21398d1ef6f626884

New changeset c1f7262f7013074613805347db2276f8b5e0e3a4 by Victor Stinner in branch 'master':
bpo-36728: Remove PyEval_ReInitThreads documentation (GH-13282)
https://github.com/python/cpython/commit/c1f7262f7013074613805347db2276f8b5e0e3a4