Revert LRU cache element optimisation

This reverts commit 6d7cdaf.

Author: Erlend E. Aasland

Modules/_functoolsmodule.c

@@ -762,10 +762,28 @@ typedef struct lru_list_elem {
     PyObject *key, *result;
 } lru_list_elem;
 
+static int
+lru_list_elem_clear(lru_list_elem *link)
+{
+    Py_CLEAR(link->key);
+    Py_CLEAR(link->result);
+    return 0;
+}
+
+static int
+lru_list_elem_traverse(lru_list_elem *link, visitproc visit, void *arg)
+{
+    Py_VISIT(link->key);
+    Py_VISIT(link->result);
+    Py_VISIT(Py_TYPE(link));
+    return 0;
+}
+
 static void
 lru_list_elem_dealloc(lru_list_elem *link)
 {
     PyTypeObject *tp = Py_TYPE(link);
+    PyObject_GC_UnTrack(link);
     Py_XDECREF(link->key);
     Py_XDECREF(link->result);
     tp->tp_free(link);
@@ -774,13 +792,16 @@ lru_list_elem_dealloc(lru_list_elem *link)
 
 static PyType_Slot lru_list_elem_type_slots[] = {
     {Py_tp_dealloc, lru_list_elem_dealloc},
+    {Py_tp_traverse, lru_list_elem_traverse},
+    {Py_tp_clear, lru_list_elem_clear},
     {0, 0}
 };
 
 static PyType_Spec lru_list_elem_type_spec = {
     .name = "functools._lru_list_elem",
     .basicsize = sizeof(lru_list_elem),
-    .flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION |
+              Py_TPFLAGS_HAVE_GC),
     .slots = lru_list_elem_type_slots
 };
 
@@ -1045,8 +1066,8 @@ bounded_lru_cache_wrapper(lru_cache_object *self, PyObject *args, PyObject *kwds
         self->root.next == &self->root)
     {
         /* Cache is not full, so put the result in a new link */
-        link = (lru_list_elem *)PyObject_New(lru_list_elem,
-                                             self->lru_list_elem_type);
+        link = (lru_list_elem *)PyObject_GC_New(lru_list_elem,
+                                                self->lru_list_elem_type);
         if (link == NULL) {
             Py_DECREF(key);
             Py_DECREF(result);
@@ -1056,6 +1077,7 @@ bounded_lru_cache_wrapper(lru_cache_object *self, PyObject *args, PyObject *kwds
         link->hash = hash;
         link->key = key;
         link->result = result;
+        PyObject_GC_Track(link);
         /* What is really needed here is a SetItem variant with a "no clobber"
            option.  If the __eq__ call triggers a reentrant call that adds
            this same key, then this setitem call will update the cache dict
@@ -1345,9 +1367,7 @@ lru_cache_tp_traverse(lru_cache_object *self, visitproc visit, void *arg)
     lru_list_elem *link = self->root.next;
     while (link != &self->root) {
         lru_list_elem *next = link->next;
-        Py_VISIT(link->key);
-        Py_VISIT(link->result);
-        Py_VISIT(Py_TYPE(link));
+        Py_VISIT(link);
         link = next;
     }
     Py_VISIT(self->cache);