[Python-3000-checkins] r64311 - in python/branches/py3k: Lib/test/test_weakref.py Misc/NEWS Objects/weakrefobject.c

[amaury.forgeotdarc]

Author: amaury.forgeotdarc
Date: Mon Jun 16 21:50:09 2008
New Revision: 64311

Log:
Merged revisions 64309 via svnmerge from 
svn+ssh://pythondev@svn.python.org/python/trunk

........
  r64309 | amaury.forgeotdarc | 2008-06-16 21:12:42 +0200 (lun., 16 juin 2008) | 8 lines
  
  Issue 3110: Crash with weakref subclass, 
  seen after a "import multiprocessing.reduction"
  
  An instance of a weakref subclass can have attributes.
  If such a weakref holds the only strong reference to the object,
  deleting the weakref will delete the object. In this case,
  the callback must not be called, because the ref object is being deleted!
........


Modified:
   python/branches/py3k/   (props changed)
   python/branches/py3k/Lib/test/test_weakref.py
   python/branches/py3k/Misc/NEWS
   python/branches/py3k/Objects/weakrefobject.c

Modified: python/branches/py3k/Lib/test/test_weakref.py
==============================================================================
--- python/branches/py3k/Lib/test/test_weakref.py	(original)
+++ python/branches/py3k/Lib/test/test_weakref.py	Mon Jun 16 21:50:09 2008
@@ -661,7 +661,7 @@
         w = Target()
 
 
-class SubclassableWeakrefTestCase(unittest.TestCase):
+class SubclassableWeakrefTestCase(TestBase):
 
     def test_subclass_refs(self):
         class MyRef(weakref.ref):
@@ -725,6 +725,44 @@
         self.assertEqual(r.meth(), "abcdef")
         self.failIf(hasattr(r, "__dict__"))
 
+    def test_subclass_refs_with_cycle(self):
+        # Bug #3110
+        # An instance of a weakref subclass can have attributes.
+        # If such a weakref holds the only strong reference to the object,
+        # deleting the weakref will delete the object. In this case,
+        # the callback must not be called, because the ref object is
+        # being deleted.
+        class MyRef(weakref.ref):
+            pass
+
+        # Use a local callback, for "regrtest -R::"
+        # to detect refcounting problems
+        def callback(w):
+            self.cbcalled += 1
+
+        o = C()
+        r1 = MyRef(o, callback)
+        r1.o = o
+        del o
+
+        del r1 # Used to crash here
+
+        self.assertEqual(self.cbcalled, 0)
+
+        # Same test, with two weakrefs to the same object
+        # (since code paths are different)
+        o = C()
+        r1 = MyRef(o, callback)
+        r2 = MyRef(o, callback)
+        r1.r = r2
+        r2.o = o
+        del o
+        del r2
+
+        del r1 # Used to crash here
+
+        self.assertEqual(self.cbcalled, 0)
+
 
 class Object:
     def __init__(self, arg):
@@ -1171,6 +1209,7 @@
         MappingTestCase,
         WeakValueDictionaryTestCase,
         WeakKeyDictionaryTestCase,
+        SubclassableWeakrefTestCase,
         )
     support.run_doctest(sys.modules[__name__])
 

Modified: python/branches/py3k/Misc/NEWS
==============================================================================
--- python/branches/py3k/Misc/NEWS	(original)
+++ python/branches/py3k/Misc/NEWS	Mon Jun 16 21:50:09 2008
@@ -12,6 +12,9 @@
 Core and Builtins
 -----------------
 
+- Issue #3100: Corrected a crash on deallocation of a subclassed weakref which
+  holds the last (strong) reference to its referent.
+
 - Issue #2630: implement PEP 3138. repr() now returns printable
   Unicode characters unescaped, to get an ASCII-only representation
   of an object use ascii().

Modified: python/branches/py3k/Objects/weakrefobject.c
==============================================================================
--- python/branches/py3k/Objects/weakrefobject.c	(original)
+++ python/branches/py3k/Objects/weakrefobject.c	Mon Jun 16 21:50:09 2008
@@ -884,7 +884,8 @@
             current->wr_callback = NULL;
             clear_weakref(current);
             if (callback != NULL) {
-                handle_callback(current, callback);
+                if (current->ob_refcnt > 0)
+                    handle_callback(current, callback);
                 Py_DECREF(callback);
             }
         }
@@ -902,9 +903,15 @@
             for (i = 0; i < count; ++i) {
                 PyWeakReference *next = current->wr_next;
 
-                Py_INCREF(current);
-                PyTuple_SET_ITEM(tuple, i * 2, (PyObject *) current);
-                PyTuple_SET_ITEM(tuple, i * 2 + 1, current->wr_callback);
+                if (current->ob_refcnt > 0)
+                {
+                    Py_INCREF(current);
+                    PyTuple_SET_ITEM(tuple, i * 2, (PyObject *) current);
+                    PyTuple_SET_ITEM(tuple, i * 2 + 1, current->wr_callback);
+                }
+                else {
+                    Py_DECREF(current->wr_callback);
+                }
                 current->wr_callback = NULL;
                 clear_weakref(current);
                 current = next;
@@ -912,6 +919,7 @@
             for (i = 0; i < count; ++i) {
                 PyObject *callback = PyTuple_GET_ITEM(tuple, i * 2 + 1);
 
+                /* The tuple may have slots left to NULL */
                 if (callback != NULL) {
                     PyObject *item = PyTuple_GET_ITEM(tuple, i * 2);
                     handle_callback((PyWeakReference *)item, callback);