Merged revisions 70546 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r70546 | antoine.pitrou | 2009-03-23 19:41:45 +0100 (lun., 23 mars 2009) | 9 lines

  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, 54 insertions, 0 deletions

diff --git a/Objects/tupleobject.c b/Objects/tupleobject.c
index 8828a2d5e6..11be0e19dc 100644
--- a/Objects/tupleobject.c
+++ b/Objects/tupleobject.c
@@ -23,11 +23,36 @@ Py_ssize_t fast_tuple_allocs;
 Py_ssize_t tuple_zero_allocs;
 #endif
 
+/* Debug statistic to count GC tracking of tuples.
+   Please note that tuples are only untracked when considered by the GC, and
+   many of them will be dead before. Therefore, a tracking rate close to 100%
+   does not necessarily prove that the heuristic is inefficient.
+*/
+#ifdef SHOW_TRACK_COUNT
+static Py_ssize_t count_untracked = 0;
+static Py_ssize_t count_tracked = 0;
+
+static void
+show_track(void)
+{
+	fprintf(stderr, "Tuples created: %" PY_FORMAT_SIZE_T "d\n",
+		count_tracked + count_untracked);
+	fprintf(stderr, "Tuples tracked by the GC: %" PY_FORMAT_SIZE_T
+		"d\n", count_tracked);
+	fprintf(stderr, "%.2f%% tuple tracking rate\n\n",
+		(100.0*count_tracked/(count_untracked+count_tracked)));
+}
+#endif
+
+
 PyObject *
 PyTuple_New(register Py_ssize_t size)
 {
 	register PyTupleObject *op;
 	Py_ssize_t i;
+#ifdef SHOW_TRACK_COUNT
+	count_tracked++;
+#endif
 	if (size < 0) {
 		PyErr_BadInternalCall();
 		return NULL;
@@ -131,6 +156,32 @@ PyTuple_SetItem(register PyObject *op, register Py_ssize_t i, PyObject *newitem)
 	return 0;
 }
 
+void
+_PyTuple_MaybeUntrack(PyObject *op)
+{
+	PyTupleObject *t;
+	Py_ssize_t i, n;
+	
+	if (!PyTuple_CheckExact(op) || !_PyObject_GC_IS_TRACKED(op))
+		return;
+	t = (PyTupleObject *) op;
+	n = Py_SIZE(t);
+	for (i = 0; i < n; i++) {
+		PyObject *elt = PyTuple_GET_ITEM(t, i);
+		/* Tuple with NULL elements aren't
+		   fully constructed, don't untrack
+		   them yet. */
+		if (!elt ||
+			_PyObject_GC_MAY_BE_TRACKED(elt))
+			return;
+	}
+#ifdef SHOW_TRACK_COUNT
+	count_tracked--;
+	count_untracked++;
+#endif
+	_PyObject_GC_UNTRACK(op);
+}
+
 PyObject *
 PyTuple_Pack(Py_ssize_t n, ...)
 {
@@ -855,6 +906,9 @@ PyTuple_Fini(void)
 
 	(void)PyTuple_ClearFreeList();
 #endif
+#ifdef SHOW_TRACK_COUNT
+	show_track();
+#endif
 }
 
 /*********************** Tuple Iterator **************************/