gh-132641: fix race in lru_cache under free-threading (#133787)

Fix race in `lru_cache` by acquiring critical section on the cache object itself and call the lock held variant of dict functions to modify the underlying dict.

Lib/test/test_free_threading/test_functools.py

@@ -0,0 +1,75 @@
+import random
+import unittest
+
+from functools import lru_cache
+from threading import Barrier, Thread
+
+from test.support import threading_helper
+
+@threading_helper.requires_working_threading()
+class TestLRUCache(unittest.TestCase):
+
+    def _test_concurrent_operations(self, maxsize):
+        num_threads = 10
+        b = Barrier(num_threads)
+        @lru_cache(maxsize=maxsize)
+        def func(arg=0):
+            return object()
+
+
+        def thread_func():
+            b.wait()
+            for i in range(1000):
+                r = random.randint(0, 1000)
+                if i < 800:
+                    func(i)
+                elif i < 900:
+                    func.cache_info()
+                else:
+                    func.cache_clear()
+
+        threads = []
+        for i in range(num_threads):
+            t = Thread(target=thread_func)
+            threads.append(t)
+
+        with threading_helper.start_threads(threads):
+            pass
+
+    def test_concurrent_operations_unbounded(self):
+        self._test_concurrent_operations(maxsize=None)
+
+    def test_concurrent_operations_bounded(self):
+        self._test_concurrent_operations(maxsize=128)
+
+    def _test_reentrant_cache_clear(self, maxsize):
+        num_threads = 10
+        b = Barrier(num_threads)
+        @lru_cache(maxsize=maxsize)
+        def func(arg=0):
+            func.cache_clear()
+            return object()
+
+
+        def thread_func():
+            b.wait()
+            for i in range(1000):
+                func(random.randint(0, 10000))
+
+        threads = []
+        for i in range(num_threads):
+            t = Thread(target=thread_func)
+            threads.append(t)
+
+        with threading_helper.start_threads(threads):
+            pass
+
+    def test_reentrant_cache_clear_unbounded(self):
+        self._test_reentrant_cache_clear(maxsize=None)
+
+    def test_reentrant_cache_clear_bounded(self):
+        self._test_reentrant_cache_clear(maxsize=128)
+
+
+if __name__ == "__main__":
+    unittest.main()