Remove unnecessary locking when reading iconv configuration [BZ #22062]

In iconv/gconv_conf.c, __gconv_get_path unnecessarily obtains a lock when
populating the array pointed to by __gconv_path_elem. The locking is not
necessary because all calls to __gconv_read_conf (which in turn calls
__gconv_get_path) are serialized using __libc_once.

This patch:
- removes all locking in __gconv_get_path;
- replaces all explicitly serialized __gconv_read_conf calls with calls to
  __gconv_load_conf, a new wrapper that is serialized internally;
- adds a new test, iconv/tst-iconv_mt.c, to exercise iconv initialization,
  usage, and cleanup in a multi-threaded program;
- indents __gconv_get_path correctly, removing tab characters (which makes
  the patch look a little bigger than it really is).

After removing the unnecessary locking, it was confirmed that the test case
fails if the relevant __libc_once is removed. Additionally, four localedata
and iconvdata tests also fail. This gives confidence that the testsuite
sufficiently guards against some regressions relating to multi-threading
with iconv.

Tested on x86_64 and i686.

1 files changed, 2 insertions, 2 deletions

diff --git a/iconv/gconv_int.h b/iconv/gconv_int.h
index 45e47a6511..dcdb1bce76 100644
--- a/iconv/gconv_int.h
+++ b/iconv/gconv_int.h
@@ -178,8 +178,8 @@ extern int __gconv_compare_alias_cache (const char *name1, const char *name2,
 extern void __gconv_release_step (struct __gconv_step *step)
      attribute_hidden;
 
-/* Read all the configuration data and cache it.  */
-extern void __gconv_read_conf (void) attribute_hidden;
+/* Read all the configuration data and cache it if not done so already.  */
+extern void __gconv_load_conf (void) attribute_hidden;
 
 /* Try to read module cache file.  */
 extern int __gconv_load_cache (void) attribute_hidden;