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Fix unsafe locale usage in wcstod_l fallback

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Using `setlocale` is both not thread-safe and not correct, as
a) The global locale is usually stored in static storage, so
   simultaneous calls to `setlocale` can result in corruption, and
b) `setlocale` changes the locale for the entire application, not
   just the calling thread. This means that even if we wrapped the
   `wcstod_l` in a mutex to prevent the previous point, the results
   would still be incorrect because this would incorrectly influence the
   results of locale-aware functions executed in other threads while
   this thread is executing.

The previous comment mentioned that `uselocale` hadn't worked. I'm not
sure what the failing implementation looked like, but `uselocale` can be
tricky. The committed implementation passes the tests for me under Linux
and FreeBSD.
This commit is contained in:
Mahmoud Al-Qudsi 2019-01-02 17:29:48 -06:00
parent bc0a0b4bc8
commit 3444e1db18
1 changed files with 6 additions and 6 deletions
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12
src/fallback.cpp
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@ -394,13 +394,13 @@ int flock(int fd, int op) {
// For platforms without wcstod_l C extension, wrap wcstod after changing the
// thread-specific locale.
double fish_compat::wcstod_l(const wchar_t *enptr, wchar_t **endptr, locale_t loc) {
char *saved_locale = strdup(setlocale(LC_NUMERIC, NULL));
// Yes, this is hardcoded to use the "C" locale.
// That's the only thing we need, and uselocale(loc) broke in my testing.
setlocale(LC_NUMERIC, "C");
// Create and use a new, thread-specific locale
locale_t locale = newlocale(LC_NUMERIC, "C", nullptr);
locale_t prev_locale = uselocale(locale);
double ret = wcstod(enptr, endptr);
setlocale(LC_NUMERIC, saved_locale);
free(saved_locale);
// Restore the old locale before freeing the locale we created and are still using
uselocale(prev_locale);
freelocale(locale);
return ret;
}
#endif // defined(wcstod_l)