localename: ensure multithread-safety in future changes

[Bruno Haible]

This patch makes sure we don't use MT-unsafe primitives in future
changes of module 'localename'.

- In function get_locale_t_name - currently not used on any platform,
  because it's in a #if HAVE_NAMELESS_LOCALES - it's better to use the
  MT-safe setlocale_null.

- In function gl_locale_name_posix, there is a call to
  setlocale (category, NULL), but only on glibc systems, where it
  happens to be MT-safe. I plan to extend this to many more systems, once
  gettext bug <https://savannah.gnu.org/bugs/?38162> is fixed. At that
  point, it will be necessary to use the MT-safe primitive.

Other than that, there is one call to setlocale (_, NULL) left. It is
MT-safe because this code is for native Windows only. Another issue,
however, is a possible circular dependency between localename.c and
setlocale.c. Better cut this circular dependency; setlocale.c is
meant to use localename.c, not the other way around.


2019-12-18  Bruno Haible  <address@hidden>

        localename: Ensure multithread-safety in future changes.
        * lib/localename.c (setlocale): Reference the system's setlocale().
        (get_locale_t_name): Invoke setlocale_null instead of setlocale.
        (gl_locale_name_posix): Likewise.
        * modules/localename (Depends-on): Add setlocale-null.

diff --git a/lib/localename.c b/lib/localename.c
index d88743e..65dddeb 100644
--- a/lib/localename.c
+++ b/lib/localename.c
@@ -1151,6 +1151,10 @@ extern char * getlocalename_l(int, locale_t);
 # endif
 #endif
 
+/* We want to use the system's setlocale() function here, not the gnulib
+   override.  */
+#undef setlocale
+
 
 #if HAVE_CFPREFERENCESCOPYAPPVALUE
 /* Mac OS X 10.4 or newer */
@@ -2725,7 +2729,7 @@ get_locale_t_name (int category, locale_t locale)
   if (locale == LC_GLOBAL_LOCALE)
     {
       /* Query the global locale.  */
-      const char *name = setlocale (category, NULL);
+      const char *name = setlocale_null (category);
       if (name != NULL)
         return struniq (name);
       else
@@ -3241,7 +3245,10 @@ gl_locale_name_posix (int category, const char 
*categoryname)
 #if defined WINDOWS_NATIVE
   if (LC_MIN <= category && category <= LC_MAX)
     {
-      const char *locname = setlocale (category, NULL);
+      const char *locname =
+        /* setlocale_null (category) is identical to setlocale (category, NULL)
+           on this platform.  */
+        setlocale (category, NULL);
 
       /* Convert locale name to LCID.  We don't want to use
          LocaleNameToLCID because (a) it is only available since Vista,
@@ -3258,7 +3265,7 @@ gl_locale_name_posix (int category, const char 
*categoryname)
     /* Use the POSIX methods of looking to 'LC_ALL', 'LC_xxx', and 'LANG'.
        On some systems this can be done by the 'setlocale' function itself.  */
 #if defined HAVE_LC_MESSAGES && defined HAVE_LOCALE_NULL
-    locname = setlocale (category, NULL);
+    locname = setlocale_null (category);
 #else
     /* On other systems we ignore what setlocale reports and instead look at 
the
        environment variables directly.  This is necessary
diff --git a/modules/localename b/modules/localename
index 9eed220..c528acb 100644
--- a/modules/localename
+++ b/modules/localename
@@ -18,6 +18,7 @@ flexmember
 strdup
 lock
 langinfo
+setlocale-null
 
 configure.ac:
 gl_LOCALENAME