subtype_dealloc(): This left the dying object exposed to gc, so that
if cyclic gc triggered during the weakref callback, gc tried to delete
the dying object a second time. That's a disaster. subtype_dealloc()
had a (I hope!) unique problem here, as every normal dealloc routine
untracks the object (from gc) before fiddling with weakrefs etc. But
subtype_dealloc has obscure technical reasons for re-registering the
dying object with gc (already explained in a large comment block at
the bottom of the function).
The fix amounts to simply refraining from reregistering the dying object
with gc until after the weakref callback (if any) has been called.
This is a critical bug (hard to predict, and causes seemingly random
memory corruption when it occurs). I'll backport it to 2.3 later.
[ 784825 ] fix obscure crash in descriptor handling
Should be applied to release23-maint and in all likelyhood
release22-maint, too.
Certainly doesn't apply to release21-maint.
Sure looks like it to me! <wink>
When I run the leak2.py script I posted to python-dev, I only see
three reference leaks in all of test_descr. When I run
test_descr.test_main, I still see 46 leaks. This clearly demands
posting a yelp to python-dev :-)
This certainly should be applied to release23-maint, and in all
likelyhood release22-maint as well.
The !PyType_Check(base) check snuck in as part of rev 2.215, but was
unrelated to the SF patch that is mentioned in the checkin comment.
The test is currently unnecessary because base is set to the return
value of best_bases(), which returns a type or NULL.
tp_free is NULL or PyObject_Del at the end. Because it's a base type
it must call tp_free in its dealloc function, and because it's gc'able
it must not call PyObject_Del.
inherit_slots(): Don't inherit tp_free unless the type and its base
agree about whether they're gc'able. If the type is gc'able and the
base is not, and the base uses the default PyObject_Del for its
tp_free, give the type PyObject_GC_Del for its tp_free (the appropriate
default for a gc'able type).
cPickle.c: The Pickler and Unpickler types claim to be base classes
and gc'able, but their dealloc functions didn't call tp_free.
Repaired that. Also call PyType_Ready() on these typeobjects, so
that the correct (PyObject_GC_Del) default memory-freeing function
gets plugged into these types' tp_free slots.
Arranged that all the objects exposed by __builtin__ appear in the list
of all objects. I basically peed away two days tracking down a mystery
leak in sys.gettotalrefcount() in a ZODB app (== tons of code), because
the object leaking the references didn't appear in the sys.getobjects(0)
list. The object happened to be False. Now False is in the list, along
with other popular & previously missing leak candidates (like None).
Alas, we still don't have a choke point covering *all* Python objects,
so the list of all objects may still be incomplete.
_Py_AddToAllObjects() that simply inserts an object at the front of
the doubly-linked list of all objects. Changed PyType_Ready() (the
closest thing we've got to a choke point for type objects) to call
that.
This still falls back to helpers in copy_reg for:
- pickle protocols < 2
- calculating the list of slot names (done only once per class)
- the __newobj__ function (which is used as a token but never called)
using super() for an instance in a metaclass situation. Because the
class was a metaclass, the instance was a class, and hence the
PyType_Check() branch was taken. But this branch didn't apply. Make
it so that if this branch doesn't apply, the other branch is still
tried. All tests pass.
This changes the default __new__ to refuse arguments iff tp_init is the
default __init__ implementation -- thus making it a TypeError when you
try to pass arguments to a constructor if the class doesn't override at
least __init__ or __new__.
Jim Fulton
Raymond Hettinger
Tim Peters
Walter Dörwald
Guido van Rossum
Michael W. Hudson
Jeremy Hylton
Brett Cannon
Neal Norwitz
Martin v. Löwis