Issue #6695: Full garbage collection runs now clear the freelist of set objects.

Initial patch by Matthias Troffaes.

Doc/c-api/set.rst

@@ -157,3 +157,10 @@ subtypes but not for instances of :class:`frozenset` or its subtypes.
 .. c:function:: int PySet_Clear(PyObject *set)
 
    Empty an existing set of all elements.
+
+
+.. c:function:: int PySet_ClearFreeList()
+
+   Clear the free list. Return the total number of freed items.
+
+   .. versionadded:: 3.3

Include/setobject.h

@@ -99,6 +99,8 @@ PyAPI_FUNC(int) _PySet_NextEntry(PyObject *set, Py_ssize_t *pos, PyObject **key,
 PyAPI_FUNC(PyObject *) PySet_Pop(PyObject *set);
 #ifndef Py_LIMITED_API
 PyAPI_FUNC(int) _PySet_Update(PyObject *set, PyObject *iterable);
+
+PyAPI_FUNC(int) PySet_ClearFreeList(void);
 #endif
 
 #ifdef __cplusplus

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.3 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #6695: Full garbage collection runs now clear the freelist of set
+  objects.  Initial patch by Matthias Troffaes.
+
 - Fix OSError.__init__ and OSError.__new__ so that each of them can be
   overriden and take additional arguments (followup to issue #12555).
 

Modules/gcmodule.c

@@ -764,6 +764,7 @@ clear_freelists(void)
     (void)PyFloat_ClearFreeList();
     (void)PyList_ClearFreeList();
     (void)PyDict_ClearFreeList();
+    (void)PySet_ClearFreeList();
 }
 
 static double

Objects/setobject.c

@@ -1068,9 +1068,10 @@ frozenset_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     return emptyfrozenset;
 }
 
-void
-PySet_Fini(void)
+int
+PySet_ClearFreeList(void)
 {
+    int freelist_size = numfree;
     PySetObject *so;
 
     while (numfree) {
@@ -1078,6 +1079,13 @@ PySet_Fini(void)
         so = free_list[numfree];
         PyObject_GC_Del(so);
     }
+    return freelist_size;
+}
+
+void
+PySet_Fini(void)
+{
+    PySet_ClearFreeList();
     Py_CLEAR(dummy);
     Py_CLEAR(emptyfrozenset);
 }