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From "Martin Sebor (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (STDCXX-1056) std::moneypunct and std::numpunct implementations are not thread-safe
Date Mon, 06 Feb 2012 21:20:59 GMT

    [ https://issues.apache.org/jira/browse/STDCXX-1056?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13201603#comment-13201603
] 

Martin Sebor commented on STDCXX-1056:
--------------------------------------

I think the problem in STDCXX-839 is that the tests run too long, not that they deadlock or
suffer from some other kind of data race.

The {{std::numpunct}} inline members were designed to be as small and as efficient as possible
to minimize code bloat and maximize iostream performance.  Adding locks to them would very
likely defeat both of these goals. If we do need additional locking it should do in one of
the out-of-line implementation functions (I think {{\_\_rw::__rw_get_punct()}} is one such
function). In any case, before we change anything in this area we need a test case to see
what's broken first, and we should also put together one that verifies that what we change
doesn't adversely affect performance.
                
> 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: stdcxx-1056.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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