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)

1 files changed, 29 insertions, 1 deletions

diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 4d71591..d9bea73 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -432,7 +432,13 @@ move_unreachable(PyGC_Head *young, PyGC_Head *unreachable)
                         (void) traverse(op,
                                         (visitproc)visit_reachable,
                                         (void *)young);
-                        next = gc->gc.gc_next;
+			next = gc->gc.gc_next;
+			if (PyTuple_CheckExact(op)) {
+				_PyTuple_MaybeUntrack(op);
+			}
+			else if (PyDict_CheckExact(op)) {
+				_PyDict_MaybeUntrack(op);
+			}
 		}
 		else {
 			/* This *may* be unreachable.  To make progress,
@@ -1264,6 +1270,26 @@ gc_get_objects(PyObject *self, PyObject *noargs)
 	return result;
 }
 
+PyDoc_STRVAR(gc_is_tracked__doc__,
+"is_tracked(obj) -> bool\n"
+"\n"
+"Returns true if the object is tracked by the garbage collector.\n"
+"Simple atomic objects will return false.\n"
+);
+
+static PyObject *
+gc_is_tracked(PyObject *self, PyObject *obj)
+{
+	PyObject *result;
+	
+	if (PyObject_IS_GC(obj) && IS_TRACKED(obj))
+		result = Py_True;
+	else
+		result = Py_False;
+	Py_INCREF(result);
+	return result;
+}
+
 
 PyDoc_STRVAR(gc__doc__,
 "This module provides access to the garbage collector for reference cycles.\n"
@@ -1278,6 +1304,7 @@ PyDoc_STRVAR(gc__doc__,
 "set_threshold() -- Set the collection thresholds.\n"
 "get_threshold() -- Return the current the collection thresholds.\n"
 "get_objects() -- Return a list of all objects tracked by the collector.\n"
+"is_tracked() -- Returns true if a given object is tracked.\n"
 "get_referrers() -- Return the list of objects that refer to an object.\n"
 "get_referents() -- Return the list of objects that an object refers to.\n");
 
@@ -1293,6 +1320,7 @@ static PyMethodDef GcMethods[] = {
 	{"collect",	   (PyCFunction)gc_collect,
          	METH_VARARGS | METH_KEYWORDS,           gc_collect__doc__},
 	{"get_objects",    gc_get_objects,METH_NOARGS,  gc_get_objects__doc__},
+	{"is_tracked",     gc_is_tracked, METH_O,       gc_is_tracked__doc__},
 	{"get_referrers",  gc_get_referrers, METH_VARARGS,
 		gc_get_referrers__doc__},
 	{"get_referents",  gc_get_referents, METH_VARARGS,