Issue #4688: Add a heuristic so that tuples and dicts containing only

untrackable objects are not tracked by the garbage collector. This can
reduce the size of collections and therefore the garbage collection overhead
on long-running programs, depending on their particular use of datatypes.

(trivia: this makes the "binary_trees" benchmark from the Computer Language
Shootout 40% faster)

3 files changed, 13 insertions, 0 deletions

diff --git a/Include/dictobject.h b/Include/dictobject.h
index b83cd0e..06e0a7e 100644
--- a/Include/dictobject.h
+++ b/Include/dictobject.h
@@ -111,6 +111,7 @@ PyAPI_FUNC(PyObject *) PyDict_Copy(PyObject *mp);
 PyAPI_FUNC(int) PyDict_Contains(PyObject *mp, PyObject *key);
 PyAPI_FUNC(int) _PyDict_Contains(PyObject *mp, PyObject *key, long hash);
 PyAPI_FUNC(PyObject *) _PyDict_NewPresized(Py_ssize_t minused);
+PyAPI_FUNC(void) _PyDict_MaybeUntrack(PyObject *mp);
 
 /* PyDict_Update(mp, other) is equivalent to PyDict_Merge(mp, other, 1). */
 PyAPI_FUNC(int) PyDict_Update(PyObject *mp, PyObject *other);
diff --git a/Include/objimpl.h b/Include/objimpl.h
index ef47218..55186b1 100644
--- a/Include/objimpl.h
+++ b/Include/objimpl.h
@@ -285,6 +285,17 @@ extern PyGC_Head *_PyGC_generation0;
 	g->gc.gc_next = NULL; \
     } while (0);
 
+/* True if the object is currently tracked by the GC. */
+#define _PyObject_GC_IS_TRACKED(o) \
+	((_Py_AS_GC(o))->gc.gc_refs != _PyGC_REFS_UNTRACKED)
+ 
+/* True if the object may be tracked by the GC in the future, or already is.
+   This can be useful to implement some optimizations. */
+#define _PyObject_GC_MAY_BE_TRACKED(obj) \
+	(PyObject_IS_GC(obj) && \
+		(!PyTuple_CheckExact(obj) || _PyObject_GC_IS_TRACKED(obj)))
+
+
 PyAPI_FUNC(PyObject *) _PyObject_GC_Malloc(size_t);
 PyAPI_FUNC(PyObject *) _PyObject_GC_New(PyTypeObject *);
 PyAPI_FUNC(PyVarObject *) _PyObject_GC_NewVar(PyTypeObject *, Py_ssize_t);
diff --git a/Include/tupleobject.h b/Include/tupleobject.h
index 58479ee..a5ab733 100644
--- a/Include/tupleobject.h
+++ b/Include/tupleobject.h
@@ -44,6 +44,7 @@ PyAPI_FUNC(int) PyTuple_SetItem(PyObject *, Py_ssize_t, PyObject *);
 PyAPI_FUNC(PyObject *) PyTuple_GetSlice(PyObject *, Py_ssize_t, Py_ssize_t);
 PyAPI_FUNC(int) _PyTuple_Resize(PyObject **, Py_ssize_t);
 PyAPI_FUNC(PyObject *) PyTuple_Pack(Py_ssize_t, ...);
+PyAPI_FUNC(void) _PyTuple_MaybeUntrack(PyObject *);
 
 /* Macro, trading safety for speed */
 #define PyTuple_GET_ITEM(op, i) (((PyTupleObject *)(op))->ob_item[i])