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[libc++][windows] Use _wsetlocale() in __locale_guard #160479

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[libc++][windows] Use _wsetlocale() in __locale_guard #160479

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16 changes: 13 additions & 3 deletions libcxx/include/__cxx03/__locale_dir/locale_base_api/locale_guard.h
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,11 @@ struct __libcpp_locale_guard {
// each category. In the second case, we know at least one category won't
// be what we want, so we only have to check the first case.
if (std::strcmp(__l.__get_locale(), __lc) != 0) {
__locale_all = _strdup(__lc);
// Use wsetlocale to query the current locale string. This avoids a lossy
// conversion of the locale string from UTF-16 to the current LC_CTYPE
// charset. The Windows CRT allows language / country strings outside of
// ASCII, e.g. "Norwegian Bokm\u00E5l_Norway.utf8".
__locale_all = _wcsdup(__wsetlocale(nullptr));
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It's a bit of a pity that this requires calling __wsetlocale() a second time after the first __setlocale() above; I'm wondering if this is a risk for performance degradation.

See e.g. #56202 for a case where this has been measured to be a bottleneck - CC @alvinhochun.

Here, I guess the alternative is to unconditionally use __wsetlocale() above for fetching the name of the current locale, and that requires us to do more of the potentially messy charset conversions. Likewise - the form that this patch suggests feels a bit asymmetrical, when both narrow and wide APIs are being used for the same thing. But I see that it would require more of a mess and more local charset conversions (and require us to decide which charset to use for conversions) if we'd switch over entirely.

So all in all, this is probably fine in this form; I think I agree that this is a reasonable compromise form.

if (__locale_all == nullptr)
__throw_bad_alloc();
__setlocale(__l.__get_locale());
Expand All @@ -57,7 +61,7 @@ struct __libcpp_locale_guard {
// for the different categories in the same format as returned by
// setlocale(LC_ALL, nullptr).
if (__locale_all != nullptr) {
__setlocale(__locale_all);
__wsetlocale(__locale_all);
free(__locale_all);
}
_configthreadlocale(__status);
Expand All @@ -68,8 +72,14 @@ struct __libcpp_locale_guard {
__throw_bad_alloc();
return __new_locale;
}
static const wchar_t* __wsetlocale(const wchar_t* __locale) {
const wchar_t* __new_locale = _wsetlocale(LC_ALL, __locale);
if (__new_locale == nullptr)
__throw_bad_alloc();
return __new_locale;
}
int __status;
char* __locale_all = nullptr;
wchar_t* __locale_all = nullptr;
};
#endif

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16 changes: 13 additions & 3 deletions libcxx/include/__locale_dir/support/windows.h
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Original file line number Diff line number Diff line change
Expand Up @@ -162,6 +162,12 @@ inline _LIBCPP_HIDE_FROM_ABI char* __setlocale(int __category, const char* __loc
std::__throw_bad_alloc();
return __new_locale;
}
inline _LIBCPP_HIDE_FROM_ABI wchar_t* __wsetlocale(int __category, const wchar_t* __locale) {
wchar_t* __new_locale = ::_wsetlocale(__category, __locale);
if (__new_locale == nullptr)
std::__throw_bad_alloc();
return __new_locale;
}
_LIBCPP_EXPORTED_FROM_ABI __lconv_t* __localeconv(__locale_t& __loc);
#endif // _LIBCPP_BUILDING_LIBRARY

Expand Down Expand Up @@ -309,7 +315,11 @@ struct __locale_guard {
// each category. In the second case, we know at least one category won't
// be what we want, so we only have to check the first case.
if (std::strcmp(__l.__get_locale(), __lc) != 0) {
__locale_all = _strdup(__lc);
// Use wsetlocale to query the current locale string. This avoids a lossy
// conversion of the locale string from UTF-16 to the current LC_CTYPE
// charset. The Windows CRT allows language / country strings outside of
// ASCII, e.g. "Norwegian Bokm\u00E5l_Norway.utf8".
__locale_all = _wcsdup(__locale::__wsetlocale(LC_ALL, nullptr));
if (__locale_all == nullptr)
std::__throw_bad_alloc();
__locale::__setlocale(LC_ALL, __l.__get_locale());
Expand All @@ -321,13 +331,13 @@ struct __locale_guard {
// for the different categories in the same format as returned by
// setlocale(LC_ALL, nullptr).
if (__locale_all != nullptr) {
__locale::__setlocale(LC_ALL, __locale_all);
__locale::__wsetlocale(LC_ALL, __locale_all);
free(__locale_all);
}
_configthreadlocale(__status);
}
int __status;
char* __locale_all = nullptr;
wchar_t* __locale_all = nullptr;
};
#endif // _LIBCPP_BUILDING_LIBRARY

Expand Down