[Python-checkins] bpo-38070: Enhance visit_decref() debug trace (GH-16631)

Victor Stinner webhook-mailer at python.org
Mon Oct 7 20:37:45 EDT 2019


https://github.com/python/cpython/commit/4d5f94b8cd20f804c7868c5395a15aa6032f874c
commit: 4d5f94b8cd20f804c7868c5395a15aa6032f874c
branch: master
author: Victor Stinner <vstinner at python.org>
committer: GitHub <noreply at github.com>
date: 2019-10-08T02:37:38+02:00
summary:

bpo-38070: Enhance visit_decref() debug trace (GH-16631)

subtract_refs() now pass the parent object to visit_decref() which
pass it to _PyObject_ASSERT(). So if the "is freed" assertion fails,
the parent is used in debug trace, rather than the freed object. The
parent object is more likely to contain useful information. Freed
objects cannot be inspected are are displayed as "<object at xxx is
freed>" with no other detail.

files:
M Modules/gcmodule.c

diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 2cbf573cf46ec..2b47abae1ae4d 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -373,9 +373,9 @@ update_refs(PyGC_Head *containers)
 
 /* A traversal callback for subtract_refs. */
 static int
-visit_decref(PyObject *op, void *data)
+visit_decref(PyObject *op, void *parent)
 {
-    _PyObject_ASSERT(op, !_PyObject_IsFreed(op));
+    _PyObject_ASSERT(_PyObject_CAST(parent), !_PyObject_IsFreed(op));
 
     if (PyObject_IS_GC(op)) {
         PyGC_Head *gc = AS_GC(op);
@@ -401,10 +401,11 @@ subtract_refs(PyGC_Head *containers)
     traverseproc traverse;
     PyGC_Head *gc = GC_NEXT(containers);
     for (; gc != containers; gc = GC_NEXT(gc)) {
-        traverse = Py_TYPE(FROM_GC(gc))->tp_traverse;
+        PyObject *op = FROM_GC(gc);
+        traverse = Py_TYPE(op)->tp_traverse;
         (void) traverse(FROM_GC(gc),
                        (visitproc)visit_decref,
-                       NULL);
+                       op);
     }
 }
 



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