New submission from STINNER Victor:
Under very low memory condition, PyErr_NoMemory() or PyErr_NormalizeException()
enters an unlimited loop when the free list of MemoryError becomes empty.
I propose to add a MemoryError read-only singleton to fix this corner case.
Attributes cannot be modified, new attributes cannot be added. MemoryError
attributes values:
* __cause__ = None
* __context__ = None
* __suppress_context__ = False
* __traceback__ = None
* args = ()
PyException_SetTraceback(), PyException_SetCause() and PyException_SetContext()
do nothing when called on the MemoryError singleton.
A MemoryError can be raised on an integer overflow when computing the size of a
memory block. In this case, you may still have available free memory and so you
may be able to build a traceback object, chain exceptions, etc.
If you consider that attributes must be modifiable in this case, we can keep
the MemoryError unchanged and keep the free list, but add a new special
"ReadOnlyMemoryError" type which has exactly one instance, preallocated at
startup (the singleton).
Read-only attributes are required to not keep references to objects when the
MemoryError (singleton) is ne more used ("destroyed"): see for example
test_memory_error_cleanup() of test_exceptions.
Python has already a PyExc_RecursionErrorInst singleton, which is used on
recursion error. It is just a preallocated RuntimeError error, attributes are
modifiable. Does this exception keep a traceback when it is no more used
("destroyed")?
Maybe using read-only attributes is overkill? Replacing the free list with a
singleton is enough?
--
See also issue #5437: before Python had a MemoryError singleton, but it was
replaced by a free list to not keep references.
changeset: 65690:c6d86439aa91
branch: 3.1
parent: 65672:e4425d68dadf
user: Antoine Pitrou <solip...@pitrou.net>
date: Thu Oct 28 23:06:57 2010 +0000
files: Include/pyerrors.h Lib/test/test_exceptions.py Misc/NEWS
Objects/exceptions.c Python/errors.c
description:
Merged revisions 85896 via svnmerge from
svn+ssh://python...@svn.python.org/python/branches/py3k
........
r85896 | antoine.pitrou | 2010-10-29 00:56:58 +0200 (ven., 29 oct. 2010) | 4
lines
Issue #5437: A preallocated MemoryError instance should not hold traceback
data (including local variables caught in the stack trace) alive infinitely.
........
--
Another option is maybe to clear frames of the traceback. Issue #17934 added a
clear() method to frame objects for that.
----------
files: memerror_singleton.patch
keywords: patch
messages: 204742
nosy: haypo
priority: normal
severity: normal
status: open
title: Add a MemoryError singleton to fix an unlimited loop when the memory is
exhausted
versions: Python 3.4
Added file: http://bugs.python.org/file32892/memerror_singleton.patch
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<http://bugs.python.org/issue19835>
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