Merged revisions 70546 via svnmerge from

pitrou · pitrou · commit 3a652b1d0af2 · 2009-03-23T18:52:06.000Z
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) ........
diff --git a/Doc/library/gc.rst b/Doc/library/gc.rst
@@ -129,6 +129,31 @@ The :mod:`gc` module provides the following functions:
    from an argument, that integer object may or may not appear in the result list.
 
 
+.. function:: is_tracked(obj)
+
+   Returns True if the object is currently tracked by the garbage collector,
+   False otherwise.  As a general rule, instances of atomic types aren't
+   tracked and instances of non-atomic types (containers, user-defined
+   objects...) are.  However, some type-specific optimizations can be present
+   in order to suppress the garbage collector footprint of simple instances
+   (e.g. dicts containing only atomic keys and values)::
+
+      >>> gc.is_tracked(0)
+      False
+      >>> gc.is_tracked("a")
+      False
+      >>> gc.is_tracked([])
+      True
+      >>> gc.is_tracked({})
+      False
+      >>> gc.is_tracked({"a": 1})
+      False
+      >>> gc.is_tracked({"a": []})
+      True
+
+   .. versionadded:: 2.7
+
+
 The following variable is provided for read-only access (you can mutate its
 value but should not rebind it):
 
diff --git a/Include/dictobject.h b/Include/dictobject.h
@@ -125,6 +125,7 @@ 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
@@ -282,6 +282,17 @@ 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
@@ -45,6 +45,7 @@ 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])
diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
@@ -665,6 +665,104 @@ class C(object):
             gc.collect()
             self.assert_(ref() is None, "Cycle was not collected")
 
+    def _not_tracked(self, t):
+        # Nested containers can take several collections to untrack
+        gc.collect()
+        gc.collect()
+        self.assertFalse(gc.is_tracked(t), t)
+
+    def _tracked(self, t):
+        self.assertTrue(gc.is_tracked(t), t)
+        gc.collect()
+        gc.collect()
+        self.assertTrue(gc.is_tracked(t), t)
+
+    def test_track_literals(self):
+        # Test GC-optimization of dict literals
+        x, y, z, w = 1.5, "a", (1, None), []
+
+        self._not_tracked({})
+        self._not_tracked({x:(), y:x, z:1})
+        self._not_tracked({1: "a", "b": 2})
+        self._not_tracked({1: 2, (None, True, False, ()): int})
+        self._not_tracked({1: object()})
+
+        # Dicts with mutable elements are always tracked, even if those
+        # elements are not tracked right now.
+        self._tracked({1: []})
+        self._tracked({1: ([],)})
+        self._tracked({1: {}})
+        self._tracked({1: set()})
+
+    def test_track_dynamic(self):
+        # Test GC-optimization of dynamically-created dicts
+        class MyObject(object):
+            pass
+        x, y, z, w, o = 1.5, "a", (1, object()), [], MyObject()
+
+        d = dict()
+        self._not_tracked(d)
+        d[1] = "a"
+        self._not_tracked(d)
+        d[y] = 2
+        self._not_tracked(d)
+        d[z] = 3
+        self._not_tracked(d)
+        self._not_tracked(d.copy())
+        d[4] = w
+        self._tracked(d)
+        self._tracked(d.copy())
+        d[4] = None
+        self._not_tracked(d)
+        self._not_tracked(d.copy())
+
+        # dd isn't tracked right now, but it may mutate and therefore d
+        # which contains it must be tracked.
+        d = dict()
+        dd = dict()
+        d[1] = dd
+        self._not_tracked(dd)
+        self._tracked(d)
+        dd[1] = d
+        self._tracked(dd)
+
+        d = dict.fromkeys([x, y, z])
+        self._not_tracked(d)
+        dd = dict()
+        dd.update(d)
+        self._not_tracked(dd)
+        d = dict.fromkeys([x, y, z, o])
+        self._tracked(d)
+        dd = dict()
+        dd.update(d)
+        self._tracked(dd)
+
+        d = dict(x=x, y=y, z=z)
+        self._not_tracked(d)
+        d = dict(x=x, y=y, z=z, w=w)
+        self._tracked(d)
+        d = dict()
+        d.update(x=x, y=y, z=z)
+        self._not_tracked(d)
+        d.update(w=w)
+        self._tracked(d)
+
+        d = dict([(x, y), (z, 1)])
+        self._not_tracked(d)
+        d = dict([(x, y), (z, w)])
+        self._tracked(d)
+        d = dict()
+        d.update([(x, y), (z, 1)])
+        self._not_tracked(d)
+        d.update([(x, y), (z, w)])
+        self._tracked(d)
+
+    def test_track_subtypes(self):
+        # Dict subtypes are always tracked
+        class MyDict(dict):
+            pass
+        self._tracked(MyDict())
+
 
 from test import mapping_tests
 
diff --git a/Lib/test/test_gc.py b/Lib/test/test_gc.py
@@ -415,6 +415,33 @@ def test_get_referents(self):
 
         self.assertEqual(gc.get_referents(1, 'a', 4j), [])
 
+    def test_is_tracked(self):
+        # Atomic built-in types are not tracked, user-defined objects and
+        # mutable containers are.
+        # NOTE: types with special optimizations (e.g. tuple) have tests
+        # in their own test files instead.
+        self.assertFalse(gc.is_tracked(None))
+        self.assertFalse(gc.is_tracked(1))
+        self.assertFalse(gc.is_tracked(1.0))
+        self.assertFalse(gc.is_tracked(1.0 + 5.0j))
+        self.assertFalse(gc.is_tracked(True))
+        self.assertFalse(gc.is_tracked(False))
+        self.assertFalse(gc.is_tracked(b"a"))
+        self.assertFalse(gc.is_tracked("a"))
+        self.assertFalse(gc.is_tracked(bytearray(b"a")))
+        self.assertFalse(gc.is_tracked(type))
+        self.assertFalse(gc.is_tracked(int))
+        self.assertFalse(gc.is_tracked(object))
+        self.assertFalse(gc.is_tracked(object()))
+
+        class UserClass:
+            pass
+        self.assertTrue(gc.is_tracked(gc))
+        self.assertTrue(gc.is_tracked(UserClass))
+        self.assertTrue(gc.is_tracked(UserClass()))
+        self.assertTrue(gc.is_tracked([]))
+        self.assertTrue(gc.is_tracked(set()))
+
     def test_bug1055820b(self):
         # Corresponds to temp2b.py in the bug report.
 
diff --git a/Lib/test/test_tuple.py b/Lib/test/test_tuple.py
@@ -1,5 +1,7 @@
 from test import support, seq_tests
 
+import gc
+
 class TupleTest(seq_tests.CommonTest):
     type2test = tuple
 
@@ -82,6 +84,69 @@ def test_repr(self):
         self.assertEqual(repr(a0), "()")
         self.assertEqual(repr(a2), "(0, 1, 2)")
 
+    def _not_tracked(self, t):
+        # Nested tuples can take several collections to untrack
+        gc.collect()
+        gc.collect()
+        self.assertFalse(gc.is_tracked(t), t)
+
+    def _tracked(self, t):
+        self.assertTrue(gc.is_tracked(t), t)
+        gc.collect()
+        gc.collect()
+        self.assertTrue(gc.is_tracked(t), t)
+
+    def test_track_literals(self):
+        # Test GC-optimization of tuple literals
+        x, y, z = 1.5, "a", []
+
+        self._not_tracked(())
+        self._not_tracked((1,))
+        self._not_tracked((1, 2))
+        self._not_tracked((1, 2, "a"))
+        self._not_tracked((1, 2, (None, True, False, ()), int))
+        self._not_tracked((object(),))
+        self._not_tracked(((1, x), y, (2, 3)))
+
+        # Tuples with mutable elements are always tracked, even if those
+        # elements are not tracked right now.
+        self._tracked(([],))
+        self._tracked(([1],))
+        self._tracked(({},))
+        self._tracked((set(),))
+        self._tracked((x, y, z))
+
+    def check_track_dynamic(self, tp, always_track):
+        x, y, z = 1.5, "a", []
+
+        check = self._tracked if always_track else self._not_tracked
+        check(tp())
+        check(tp([]))
+        check(tp(set()))
+        check(tp([1, x, y]))
+        check(tp(obj for obj in [1, x, y]))
+        check(tp(set([1, x, y])))
+        check(tp(tuple([obj]) for obj in [1, x, y]))
+        check(tuple(tp([obj]) for obj in [1, x, y]))
+
+        self._tracked(tp([z]))
+        self._tracked(tp([[x, y]]))
+        self._tracked(tp([{x: y}]))
+        self._tracked(tp(obj for obj in [x, y, z]))
+        self._tracked(tp(tuple([obj]) for obj in [x, y, z]))
+        self._tracked(tuple(tp([obj]) for obj in [x, y, z]))
+
+    def test_track_dynamic(self):
+        # Test GC-optimization of dynamically constructed tuples.
+        self.check_track_dynamic(tuple, False)
+
+    def test_track_subtypes(self):
+        # Tuple subtypes must always be tracked
+        class MyTuple(tuple):
+            pass
+        self.check_track_dynamic(MyTuple, True)
+
+
 def test_main():
     support.run_unittest(TupleTest)
 
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -12,6 +12,11 @@ What's New in Python 3.1 alpha 2?
 Core and Builtins
 -----------------
 
+- 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.
+
 - Issue #5512: Rewrite PyLong long division algorithm (x_divrem) to
   improve its performance.  Long divisions and remainder operations
   are now between 50% and 150% faster.
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
@@ -433,7 +433,13 @@ 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,
@@ -1229,6 +1235,26 @@ 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"
@@ -1243,6 +1269,7 @@ 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");
 
@@ -1258,6 +1285,7 @@ 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,
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
diff --git a/Objects/tupleobject.c b/Objects/tupleobject.c
