Fixed #33252 -- Made cache middlewares thread-safe.

tests/cache/tests.py

@@ -2488,6 +2488,21 @@ class CacheMiddlewareTest(SimpleTestCase):
         self.assertIn('Cache-Control', response)
         self.assertIn('Expires', response)
 
+    def test_per_thread(self):
+        """The cache instance is different for each thread."""
+        thread_caches = []
+        middleware = CacheMiddleware(empty_response)
+
+        def runner():
+            thread_caches.append(middleware.cache)
+
+        for _ in range(2):
+            thread = threading.Thread(target=runner)
+            thread.start()
+            thread.join()
+
+        self.assertIsNot(thread_caches[0], thread_caches[1])
+
 
 @override_settings(
     CACHE_MIDDLEWARE_KEY_PREFIX='settingsprefix',