gethostbyname_r is not thread-safe

[Rei Takahashi]

Hello
Please allow my poor English.(I'm Japanese)

In glibc-2.2.5, I get this message while running multi-threaded program.
> /etc/host.conf: line 1: cannot specify more than 4 services

In my survey, I think that 'gethostbyname_r()' has a little bug.

'gethostbyname_r()' is implemented in 'nss/getXXbyYY_r.c'.
'_res_hconf' is GLOBAL-variable, but

> #ifdef NEED__RES_HCONF
>           if (!_res_hconf.initialized)
>             _res_hconf_init ();
> #endif /* need _res_hconf */

is not locked!
It causes call '_res_hconf_init()' two or more times concurrently.
This occurs first-call 'gethostbyname_r' by process, so this problem is
rare.
(So, I can avoid it by calling dummy 'gethostbyname_r()' before creating
thread.)

This causes executing
> _res_hconf.service[_res_hconf.num_services++] = service;
concurrently, and
> if (_res_hconf.num_services >= SERVICE_MAX)
makes be true, so I get that message.(resolv/res_hconf.c)

Please fix it if you can get my explanation.

--
Rei Takahashi
Future Spirits Co.,Ltd. / Japan