diff --git a/Include/object.h b/Include/object.h
index c772dea..5729797 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -1098,6 +1098,49 @@ PyAPI_FUNC(void)
_PyObject_DebugTypeStats(FILE *out);
#endif /* ifndef Py_LIMITED_API */
+/*
+ Define a pair of assertion macros.
+
+ These work like the regular C assert(), in that they will abort the
+ process with a message on stderr if the given condition fails to hold,
+ but compile away to nothing if NDEBUG is defined.
+
+ However, before aborting, Python will also try to call _PyObject_Dump() on
+ the given object. This may be of use when investigating bugs in which a
+ particular object is corrupt (e.g. buggy a tp_visit method in an extension
+ module breaking the garbage collector), to help locate the broken objects.
+
+ The WITH_MSG variant allows you to supply an additional message that Python
+ will attempt to print to stderr, after the object dump.
+*/
+#ifdef NDEBUG
+/* No debugging: compile away the assertions: */
+#define PyObject_ASSERT_WITH_MSG(obj, expr, msg) ((void)0)
+#else
+/* With debugging: generate checks: */
+#define PyObject_ASSERT_WITH_MSG(obj, expr, msg) \
+ ((expr) \
+ ? (void)(0) \
+ : _PyObject_AssertFailed((obj), \
+ (msg), \
+ (__STRING(expr)), \
+ (__FILE__), \
+ (__LINE__), \
+ (__PRETTY_FUNCTION__)))
+#endif
+
+#define PyObject_ASSERT(obj, expr) \
+ PyObject_ASSERT_WITH_MSG(obj, expr, NULL)
+
+/*
+ Declare and define the entrypoint even when NDEBUG is defined, to avoid
+ causing compiler/linker errors when building extensions without NDEBUG
+ against a Python built with NDEBUG defined
+*/
+PyAPI_FUNC(void) _PyObject_AssertFailed(PyObject *, const char *,
+ const char *, const char *, int,
+ const char *);
+
#ifdef __cplusplus
}
#endif
diff --git a/Lib/test/test_gc.py b/Lib/test/test_gc.py
index 8d806db..dc8bb16 100644
--- a/Lib/test/test_gc.py
+++ b/Lib/test/test_gc.py
@@ -1,10 +1,12 @@
import unittest
from test.support import (verbose, refcount_test, run_unittest,
strip_python_stderr, cpython_only, start_threads,
- temp_dir, requires_type_collecting, TESTFN, unlink)
+ temp_dir, requires_type_collecting, TESTFN, unlink,
+ import_module)
from test.support.script_helper import assert_python_ok, make_script
import sys
+import sysconfig
import time
import gc
import weakref
@@ -46,6 +48,8 @@ class GC_Detector(object):
# gc collects it.
self.wr = weakref.ref(C1055820(666), it_happened)
+BUILD_WITH_NDEBUG = ('-DNDEBUG' in sysconfig.get_config_vars()['PY_CFLAGS'])
+
@with_tp_del
class Uncollectable(object):
"""Create a reference cycle with multiple __del__ methods.
@@ -878,6 +882,50 @@ class GCCallbackTests(unittest.TestCase):
self.assertEqual(len(gc.garbage), 0)
+ @unittest.skipIf(BUILD_WITH_NDEBUG,
+ 'built with -NDEBUG')
+ def test_refcount_errors(self):
+ self.preclean()
+ # Verify the "handling" of objects with broken refcounts
+ import_module("ctypes") #skip if not supported
+
+ import subprocess
+ code = '''if 1:
+ a = []
+ b = [a]
+
+ # Simulate the refcount of "a" being too low (compared to the
+ # references held on it by live data), but keeping it above zero
+ # (to avoid deallocating it):
+ import ctypes
+ ctypes.pythonapi.Py_DecRef(ctypes.py_object(a))
+
+ # The garbage collector should now have a fatal error when it reaches
+ # the broken object:
+ import gc
+ gc.collect()
+ '''
+ p = subprocess.Popen([sys.executable, "-c", code],
+ stdout=subprocess.PIPE,
+ stderr=subprocess.PIPE)
+ stdout, stderr = p.communicate()
+ p.stdout.close()
+ p.stderr.close()
+ # Verify that stderr has a useful error message:
+ self.assertRegex(stderr,
+ b'Modules/gcmodule.c:[0-9]+: visit_decref: Assertion "\(\(gc\)->gc.gc_refs >> \(1\)\) != 0" failed.')
+ self.assertRegex(stderr,
+ b'refcount was too small')
+ self.assertRegex(stderr,
+ b'object : \[\]')
+ self.assertRegex(stderr,
+ b'type : list')
+ self.assertRegex(stderr,
+ b'refcount: 1')
+ self.assertRegex(stderr,
+ b'address : 0x[0-9a-f]+')
+
+
class GCTogglingTests(unittest.TestCase):
def setUp(self):
gc.enable()
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 4d701cb..388dd78 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -239,7 +239,8 @@ update_refs(PyGC_Head *containers)
{
PyGC_Head *gc = containers->gc.gc_next;
for (; gc != containers; gc = gc->gc.gc_next) {
- assert(_PyGCHead_REFS(gc) == GC_REACHABLE);
+ PyObject_ASSERT(FROM_GC(gc),
+ _PyGCHead_REFS(gc) == GC_REACHABLE);
_PyGCHead_SET_REFS(gc, Py_REFCNT(FROM_GC(gc)));
/* Python's cyclic gc should never see an incoming refcount
* of 0: if something decref'ed to 0, it should have been
@@ -259,7 +260,8 @@ update_refs(PyGC_Head *containers)
* so serious that maybe this should be a release-build
* check instead of an assert?
*/
- assert(_PyGCHead_REFS(gc) != 0);
+ PyObject_ASSERT(FROM_GC(gc),
+ _PyGCHead_REFS(gc) != 0);
}
}
@@ -274,7 +276,9 @@ visit_decref(PyObject *op, void *data)
* generation being collected, which can be recognized
* because only they have positive gc_refs.
*/
- assert(_PyGCHead_REFS(gc) != 0); /* else refcount was too small */
+ PyObject_ASSERT_WITH_MSG(FROM_GC(gc),
+ _PyGCHead_REFS(gc) != 0,
+ "refcount was too small"); /* else refcount was too small */
if (_PyGCHead_REFS(gc) > 0)
_PyGCHead_DECREF(gc);
}
@@ -334,9 +338,10 @@ visit_reachable(PyObject *op, PyGC_Head *reachable)
* If gc_refs == GC_UNTRACKED, it must be ignored.
*/
else {
- assert(gc_refs > 0
- || gc_refs == GC_REACHABLE
- || gc_refs == GC_UNTRACKED);
+ PyObject_ASSERT(FROM_GC(gc),
+ gc_refs > 0
+ || gc_refs == GC_REACHABLE
+ || gc_refs == GC_UNTRACKED);
}
}
return 0;
@@ -378,7 +383,7 @@ move_unreachable(PyGC_Head *young, PyGC_Head *unreachable)
*/
PyObject *op = FROM_GC(gc);
traverseproc traverse = Py_TYPE(op)->tp_traverse;
- assert(_PyGCHead_REFS(gc) > 0);
+ PyObject_ASSERT(op, _PyGCHead_REFS(gc) > 0);
_PyGCHead_SET_REFS(gc, GC_REACHABLE);
(void) traverse(op,
(visitproc)visit_reachable,
@@ -441,7 +446,7 @@ move_legacy_finalizers(PyGC_Head *unreachable, PyGC_Head *finalizers)
for (gc = unreachable->gc.gc_next; gc != unreachable; gc = next) {
PyObject *op = FROM_GC(gc);
- assert(IS_TENTATIVELY_UNREACHABLE(op));
+ PyObject_ASSERT(op, IS_TENTATIVELY_UNREACHABLE(op));
next = gc->gc.gc_next;
if (has_legacy_finalizer(op)) {
@@ -517,7 +522,7 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
PyWeakReference **wrlist;
op = FROM_GC(gc);
- assert(IS_TENTATIVELY_UNREACHABLE(op));
+ PyObject_ASSERT(op, IS_TENTATIVELY_UNREACHABLE(op));
next = gc->gc.gc_next;
if (! PyType_SUPPORTS_WEAKREFS(Py_TYPE(op)))
@@ -538,9 +543,9 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
* the callback pointer intact. Obscure: it also
* changes *wrlist.
*/
- assert(wr->wr_object == op);
+ PyObject_ASSERT(wr->wr_object, wr->wr_object == op);
_PyWeakref_ClearRef(wr);
- assert(wr->wr_object == Py_None);
+ PyObject_ASSERT(wr->wr_object, wr->wr_object == Py_None);
if (wr->wr_callback == NULL)
continue; /* no callback */
@@ -574,7 +579,7 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
*/
if (IS_TENTATIVELY_UNREACHABLE(wr))
continue;
- assert(IS_REACHABLE(wr));
+ PyObject_ASSERT(op, IS_REACHABLE(wr));
/* Create a new reference so that wr can't go away
* before we can process it again.
@@ -583,7 +588,8 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
/* Move wr to wrcb_to_call, for the next pass. */
wrasgc = AS_GC(wr);
- assert(wrasgc != next); /* wrasgc is reachable, but
+ PyObject_ASSERT(op, wrasgc != next);
+ /* wrasgc is reachable, but
next isn't, so they can't
be the same */
gc_list_move(wrasgc, &wrcb_to_call);
@@ -599,11 +605,11 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
gc = wrcb_to_call.gc.gc_next;
op = FROM_GC(gc);
- assert(IS_REACHABLE(op));
- assert(PyWeakref_Check(op));
+ PyObject_ASSERT(op, IS_REACHABLE(op));
+ PyObject_ASSERT(op, PyWeakref_Check(op));
wr = (PyWeakReference *)op;
callback = wr->wr_callback;
- assert(callback != NULL);
+ PyObject_ASSERT(op, callback != NULL);
/* copy-paste of weakrefobject.c's handle_callback() */
temp = PyObject_CallFunctionObjArgs(callback, wr, NULL);
@@ -717,12 +723,14 @@ check_garbage(PyGC_Head *collectable)
for (gc = collectable->gc.gc_next; gc != collectable;
gc = gc->gc.gc_next) {
_PyGCHead_SET_REFS(gc, Py_REFCNT(FROM_GC(gc)));
- assert(_PyGCHead_REFS(gc) != 0);
+ PyObject_ASSERT(FROM_GC(gc),
+ _PyGCHead_REFS(gc) != 0);
}
subtract_refs(collectable);
for (gc = collectable->gc.gc_next; gc != collectable;
gc = gc->gc.gc_next) {
- assert(_PyGCHead_REFS(gc) >= 0);
+ PyObject_ASSERT(FROM_GC(gc),
+ _PyGCHead_REFS(gc) >= 0);
if (_PyGCHead_REFS(gc) != 0)
return -1;
}
diff --git a/Objects/object.c b/Objects/object.c
index 220aa90..f6c7161 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -2177,6 +2177,35 @@ _PyTrash_thread_destroy_chain(void)
--tstate->trash_delete_nesting;
}
+PyAPI_FUNC(void)
+_PyObject_AssertFailed(PyObject *obj, const char *msg, const char *expr,
+ const char *file, int line, const char *function)
+{
+ fprintf(stderr,
+ "%s:%d: %s: Assertion \"%s\" failed.\n",
+ file, line, function, expr);
+ if (msg) {
+ fprintf(stderr, "%s\n", msg);
+ }
+
+ fflush(stderr);
+
+ if (obj) {
+ /* This might succeed or fail, but we're about to abort, so at least
+ try to provide any extra info we can: */
+ _PyObject_Dump(obj);
+ }
+ else {
+ fprintf(stderr, "NULL object\n");
+ }
+
+ fflush(stdout);
+ fflush(stderr);
+
+ /* Terminate the process: */
+ abort();
+}
+
#ifndef Py_TRACE_REFS
/* For Py_LIMITED_API, we need an out-of-line version of _Py_Dealloc.
Define this here, so we can undefine the macro. */