Re: POSIX gettext() and uselocale()

[Jilles Tjoelker]

On Tue, May 04, 2021 at 01:07:39AM +0200, Bruno Haible via
austin-group-l at The Open Group wrote:
> https://posix.rhansen.org/p/gettext_split
> says (line 92):

>   "The returned string may be invalidated by a subsequent call to
>    bind_textdomain_codeset(), bindtextdomain(), setlocale(),
>    textdomain(), or uselocale()."

> While in most programs setlocale(), textdomain(), bindtextdomain(),
> bind_textdomain_codeset() are being called at the beginning of the
> program execution, before any call to gettext(), the situation is
> very different for uselocale().

> 1) uselocale() is meant to have effects ONLY on the thread in which it
>    is called.

> 2) uselocale() is a helper function to implement *_l functions where
>    the POSIX standard does not specify them or the system does not have
>    them.
>    For example, when a program wants to have a function to parse
>    a number, recognizing only the ASCII digits and only '.' as decimal
>    separator, a reliable way to implement such a function is by calling
>    uselocale of the "C" locale, strtod(), and then uselocale() again
>    to switch the thread back to the previous locale.

>    If POSIX did not have uselocale(), it would need to provide many
>    more *_l functions.

> If the gettext() result may be invalidated by a uselocale() call (in
> any other thread!), this would mean that

>   ** Programs can use gettext() or uselocale() but not both. **

> and - more or less -

>   ** Multithreaded programs that use libraries (that may use uselocale())
>      cannot use gettext(). **

> I think that specifying gettext() to be so restricted is not useful.
> It would make more sense to allow concurrent uselocale() calls.

> Proposed wording:

>   "The returned string may be invalidated by a subsequent call to
>    bind_textdomain_codeset(), bindtextdomain(), setlocale(),
>    or textdomain()."

This may be a bit too weak. Now the implementation can never free a
string that was returned by a gettext call on a thread with uselocale()
active, while logically the string may be owned by the locale and could
be freed if that locale is no longer set on any thread and freelocale()
has been called on it as needed.

-- 
Jilles Tjoelker