gh-126895: fix readline module in free-threaded build

Lib/test/test_readline.py

@@ -6,7 +6,10 @@
 import sys
 import tempfile
 import textwrap
+import threading
 import unittest
+from test import support
+from test.support import threading_helper
 from test.support import verbose
 from test.support.import_helper import import_module
 from test.support.os_helper import unlink, temp_dir, TESTFN
@@ -403,5 +406,49 @@ def test_write_read_limited_history(self):
         # See TestHistoryManipulation for the full test.
 
 
+@unittest.skipUnless(support.Py_GIL_DISABLED, 'these tests can only possibly fail with GIL disabled')
+class FreeThreadingTest(unittest.TestCase):
+    def check(self, funcs, *args):
+        barrier = threading.Barrier(len(funcs))
+        threads = []
+
+        for func in funcs:
+            thread = threading.Thread(target=func, args=(barrier, *args))
+
+            threads.append(thread)
+
+        with threading_helper.start_threads(threads):
+            pass
+
+    @threading_helper.reap_threads
+    @threading_helper.requires_working_threading()
+    def test_free_threading(self):
+        def completer_delims(b):
+            b.wait()
+            for _ in range(100):
+                readline.get_completer_delims()
+                readline.set_completer_delims(' \t\n`@#%^&*()=+[{]}\\|;:\'",<>?')
+                readline.set_completer_delims(' \t\n`@#%^&*()=+[{]}\\|;:\'",<>?')
+                readline.get_completer_delims()
+
+        self.check([completer_delims] * 100)
+
+    def test_free_threading_doctest_difflib(self):
+        code = textwrap.dedent("""
+            from threading import Thread
+            import doctest, difflib
+
+            def _test():
+                try:
+                    doctest.testmod(difflib)
+                except RecursionError:
+                    pass
+
+            for x in range(40):
+                Thread(target=_test, args=()).start()
+        """)
+        assert_python_ok("-c", code)
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2025-03-13-19-54-57.gh-issue-126895.eJP9l0.rst

@@ -0,0 +1 @@
+Fix :mod:`readline` in :term:`free-threaded <free threading>` build.