Destructing `_datetime` in sub-interpreters in the same time may crash the process

[aisk]

Crash report

What happened?

from concurrent.futures import InterpreterPoolExecutor


executor = InterpreterPoolExecutor()


def f():
 import _datetime
 print(_datetime)


executor.submit(f)
executor.submit(f)

executor.shutdown()

This code may lead to a interpreter crash:

PS C:\Users\xxxxx\Source\cpython> .\python.bat .\a.py
Running Debug|x64 interpreter...
<module '_datetime' (built-in)>
<module '_datetime' (built-in)>
Debug memory block at address p=000002340D505A70: API '?
 15987178197214944733 bytes originally requested
 The 7 pad bytes at p-7 are not all FORBIDDENBYTE (0xfd):
 at p-7: 0xdd *** OUCH
 at p-6: 0xdd *** OUCH
 at p-5: 0xdd *** OUCH
 at p-4: 0xdd *** OUCH
 at p-3: 0xdd *** OUCH
 at p-2: 0xdd *** OUCH
 at p-1: 0xdd *** OUCH
 Because memory is corrupted at the start, the count of bytes requested
 may be bogus, and checking the trailing pad bytes may segfault.
 The 8 pad bytes at tail=DDDDE011EB2E384D are

I think there is a double free here.

Please note that there is a similar issue may crash the interpreter but in the initializing phase: #136421

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS, Windows

Output from running 'python -VV' on the command line:

Python 3.15.0a0 (heads/main:ba9c1986305, Jul 8 2025, 22:13:18) [MSC v.1943 64 bit (AMD64)]

[aisk]

cc @ericsnowcurrently

[seuwebber]

I encountered the same bug while using the C Python API.

[neonene]

It seems like Py_TPFLAGS_READY is cleared before managed_static_type_state_clear(), which conficts with _PyStaticType_InitForExtension() then crashes at _PyObject_ClearFreeLists().

cpython/Objects/typeobject.c

Lines 6606 to 6616 in db47f4d

	if (final) {
	BEGIN_TYPE_LOCK();
	type_clear_flags(type, Py_TPFLAGS_READY);
	set_version_unlocked(type, 0);
	END_TYPE_LOCK();
	}
	_PyStaticType_ClearWeakRefs(interp, type);
	managed_static_type_state_clear(interp, type, isbuiltin, final);
	/* We leave _Py_TPFLAGS_STATIC_BUILTIN set on tp_flags. */
	}

managed_static_type_state_clear() invokes:

cpython/Objects/typeobject.c

Lines 254 to 258 in db47f4d

	static inline void
	managed_static_type_index_clear(PyTypeObject *self)
	{
	self->tp_subclasses = NULL;
	}

So, a possible workaround only for this issue would be:

 int
 _PyStaticType_InitForExtension(PyInterpreterState *interp, PyTypeObject *self)
 {
- return init_static_type(interp, self, 0, ((self->tp_flags & Py_TPFLAGS_READY) == 0));
+ return init_static_type(interp, self, 0, self->tp_subclasses == NULL);
 }

[kumaraditya303]

Fixed by #136583