On 09/25/2012 06:08 PM, Wojciech Meyer wrote:
Hi guys,
I think the consensus about this bug is that everybody wants to fix it.
Stefan has a patch but I got completely lost what is the exact reason of
not applying it. It would be a shame to stop at this point.
From my POV, there's no disagreement that there is a bug
in the thread safety of the facets or its cause, or a lack
of desire to fix it. I think the main reason for the lack
of consensus on a patch is that we don't yet have a good
sense of the performance impact of the proposed approaches
or an understanding of the differences in the timings.
As for Stefan's patches, the biggest problem I see there
(besides the above) is that they introduce changes that
appear to be unrelated to the problem without providing
a satisfactory rationale. The established stdcxx bug
fixing process is to create as small a patch as possible
that does nothing but address the problem. This is
particularly important when we don't have ready access
to test the patch with all the targeted compilers and
on all the targeted operating systems (to minimize the
risk of incidental breakage and to make it as easy as
possible to root cause possible regressions.
Martin
Liviu Nicoara <nikko...@hates.ms> writes:
On 9/25/12 7:56 PM, Stefan Teleman (JIRA) wrote:
[
https://issues.apache.org/jira/browse/STDCXX-1056?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Stefan,
I don't think it's ok to close this bug. The race conditions are there
and we have not come to a completely satisfactory conclusion on how to
deal with them, or even if we should deal with them. Whichever it is
we gotta keep this discussion open. I sure hope you want to be a part
of it.
FWIW, I have spent quite some time looking at your proposed patch and
I am going to reopen the incident. If I can.
Liviu
Stefan Teleman closed STDCXX-1056.
----------------------------------
Resolution: Won't Fix
Bug will not be fixed. Upstream refuses to acknowledge the existence of the bug
in spite of objective evidence to the contrary.
std::moneypunct and std::numpunct implementations are not thread-safe
---------------------------------------------------------------------
Key: STDCXX-1056
URL: https://issues.apache.org/jira/browse/STDCXX-1056
Project: C++ Standard Library
Issue Type: Bug
Components: 22. Localization
Affects Versions: 4.2.1, 4.2.x, 4.3.x, 5.0.0
Environment: Solaris 10 and 11, RedHat and OpenSuSE Linux, Sun C++
Compilers 12.1, 12.2, 12.3
Issue is independent of platform and/or compiler.
Reporter: Stefan Teleman
Labels: thread-safety
Fix For: 4.2.x, 4.3.x, 5.0.0
Attachments: 22.locale.numpunct.mt.out, facet.cpp.diff,
locale_body.cpp.diff, punct.cpp.diff, runtests-linux32-all.out,
runtests-linux64-all.out, runtests.out, STDCXX-1056-additional-timings.tgz,
stdcxx-1056.patch, stdcxx-1056-timings.tgz,
stdcxx-4.2.x-numpunct-perfect-forwarding.patch,
stdcxx-4.3.x-numpunct-perfect-forwarding.patch
several member functions in std::moneypunct<> and std::numpunct<> return
a std::string by value (as required by the Standard). The implication of
return-by-value
being that the caller "owns" the returned object.
In the stdcxx implementation, the std::basic_string copy constructor uses a
shared
underlying buffer implementation. This shared buffer creates the first problem
for
these classes: although the std::string object returned by value *appears* to
be owned
by the caller, it is, in fact, not.
In a mult-threaded environment, this underlying shared buffer can be
subsequently modified by a different thread than the one who made the initial
call. Furthermore, two or more different threads can access the same shared
buffer at the same time, and modify it, resulting in undefined run-time
behavior.
The cure for this defect has two parts:
1. the member functions in question must truly return a copy by avoiding a call
to the copy constructor, and using a constructor which creates a deep copy of
the std::string.
2. access to these member functions must be serialized, in order to guarantee
atomicity
of the creation of the std::string being returned by value.
Patch for 4.2.1 to follow.
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Wojciech Meyer
http://danmey.org
