gh-104690 Disallow thread creation and fork at interpreter finalization (#104826)

Disallow thread creation and fork at interpreter finalization.

in the following functions, check if interpreter is finalizing and raise `RuntimeError` with appropriate message:
* `_thread.start_new_thread` and thus `threading`
* `posix.fork`
* `posix.fork1`
* `posix.forkpty`
* `_posixsubprocess.fork_exec` when a `preexec_fn=` is supplied.

---------

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>

Lib/test/test_subprocess.py

@@ -5,6 +5,7 @@ from test.support import check_sanitizer
 from test.support import import_helper
 from test.support import os_helper
 from test.support import warnings_helper
+from test.support.script_helper import assert_python_ok
 import subprocess
 import sys
 import signal
@@ -3329,6 +3330,24 @@ class POSIXProcessTestCase(BaseTestCase):
             except subprocess.TimeoutExpired:
                 pass
 
+    def test_preexec_at_exit(self):
+        code = f"""if 1:
+        import atexit
+        import subprocess
+
+        def dummy():
+            pass
+
+        def exit_handler():
+            subprocess.Popen({ZERO_RETURN_CMD}, preexec_fn=dummy)
+            print("shouldn't be printed")
+
+        atexit.register(exit_handler)
+        """
+        _, out, err = assert_python_ok("-c", code)
+        self.assertEqual(out, b'')
+        self.assertIn(b"preexec_fn not supported at interpreter shutdown", err)
+
 
 @unittest.skipUnless(mswindows, "Windows specific tests")
 class Win32ProcessTestCase(BaseTestCase):