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https://issues.apache.org/jira/browse/STDCXX-792?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12581767#action_12581767
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Martin Sebor commented on STDCXX-792:
-------------------------------------
I don't think the patch is safe. In particular, without the {{volatile}}
qualifier an optimizer would be free to turn the {{while}} loop below into an
infinite loop.
{noformat}
808 static volatile long ginit /* = 0 */;
809
810 if (!ginit && 1 == _RWSTD_ATOMIC_PREINCREMENT (ginit,
false)) {
811 global = _C_manage (0, "C");
812 ginit += 1000;
813 }
814 else {
815 while (ginit < 1000);
816 }
{noformat}
I agree that we should change the {{__rw_atomic_xxx()}} functions to take a
{{volatile}}-qualified argument and also that such a change would probably be
binary incompatible. What we might want to do in the meantime is either cast
away the {{volatile}} qualifier in the invocation of the
{{_RWSTD_ATOMIC_PREINCREMENT()}} macro or change the definition of the macro
itself to this effect.
> __rw_locale::_C_manage() uses mutex based __rw_atomic_preincrement() even if
> platform supports the native atomic operations
> ---------------------------------------------------------------------------------------------------------------------------
>
> Key: STDCXX-792
> URL: https://issues.apache.org/jira/browse/STDCXX-792
> Project: C++ Standard Library
> Issue Type: Bug
> Components: 22. Localization
> Affects Versions: 4.1.2, 4.1.3, 4.1.4, 4.2.0
> Environment: All
> Reporter: Farid Zaripov
> Assignee: Farid Zaripov
> Fix For: 4.2.1
>
> Original Estimate: 0.5h
> Remaining Estimate: 0.5h
>
> In __rw_locale::_C_manage() (src/locale_body.cpp, line 808), the static
> variable ginit declared as volatile, but __rw_atomic_preincrement()
> functions, which are implemented using atomic operations, accepting the
> non-volatile reference in parameter list. As a result the template version
> __rw_atomic_preincrement<volatile long>() (which is implemented using mutex
> object) is used.
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