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From Martin Sebor <mse...@gmail.com>
Subject Re: [jira] [Closed] (STDCXX-1056) std::moneypunct and std::numpunct implementations are not thread-safe
Date Wed, 26 Sep 2012 02:58:12 GMT
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 <nikkoara@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.
>>>
>>> --
>>> This message is automatically generated by JIRA.
>>> If you think it was sent incorrectly, please contact your JIRA administrators
>>> For more information on JIRA, see: http://www.atlassian.com/software/jira
>>>
>>
>
> --
> Wojciech Meyer
> http://danmey.org
>


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