gh-116738: Make _suggestions module thread-safe (gh-140321)

Author: yoney

Lib/test/test_free_threading/test_suggestions.py

@@ -0,0 +1,24 @@
+import unittest
+
+from test.support import import_helper, threading_helper
+from test.support.threading_helper import run_concurrently
+
+suggestions = import_helper.import_module("_suggestions")
+
+NTHREADS = 10
+
+
+@threading_helper.requires_working_threading()
+class SuggestionsTests(unittest.TestCase):
+    def test_generate_suggestions(self):
+        candidates = [str(i) for i in range(100)]
+
+        def worker():
+            _ = suggestions._generate_suggestions(candidates, "42")
+            candidates.clear()
+
+        run_concurrently(worker_func=worker, nthreads=NTHREADS)
+
+
+if __name__ == "__main__":
+    unittest.main()

Misc/NEWS.d/next/Core_and_Builtins/2025-10-18-19-52-20.gh-issue-116738.NLJW0L.rst

@@ -0,0 +1,2 @@
+Make _suggestions module thread-safe on the :term:`free threaded <free
+threading>` build.

Modules/_suggestions.c

@@ -8,6 +8,7 @@ module _suggestions
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=e58d81fafad5637b]*/
 
 /*[clinic input]
+@critical_section candidates
 _suggestions._generate_suggestions
     candidates: object
     item: unicode
@@ -18,7 +19,7 @@ Returns the candidate in candidates that's closest to item
 static PyObject *
 _suggestions__generate_suggestions_impl(PyObject *module,
                                         PyObject *candidates, PyObject *item)
-/*[clinic end generated code: output=79be7b653ae5e7ca input=ba2a8dddc654e33a]*/
+/*[clinic end generated code: output=79be7b653ae5e7ca input=92861a6c9bd8f667]*/
 {
    // Check if dir is a list
     if (!PyList_CheckExact(candidates)) {
@@ -29,7 +30,7 @@ _suggestions__generate_suggestions_impl(PyObject *module,
     // Check if all elements in the list are Unicode
     Py_ssize_t size = PyList_Size(candidates);
     for (Py_ssize_t i = 0; i < size; ++i) {
-        PyObject *elem = PyList_GetItem(candidates, i);
+        PyObject *elem = PyList_GET_ITEM(candidates, i);
         if (!PyUnicode_Check(elem)) {
             PyErr_SetString(PyExc_TypeError, "all elements in 'candidates' must be strings");
             return NULL;