Re: __USE_UNIX98 to enable late pthread features

[Eric Blake]

On 08/23/2010 11:28 AM, John Calcote wrote:
>   Hi all,
>
> I ran into an interesting issue today. Hoping some of you have some
> insight for me. I needed to use a later addition to the pthreads spec -
> pthread_mutexaddr_settype (in order to initialize a recursive mutex). To
> use this function, you need to define __USE_UNIX98 before including
> pthread.h - at least on my platform (opensuse 11.3 64-bit).

Are you using the AC_USE_SYSTEM_EXTENSIONS macro, prior to anything else 
that probes the C compiler?  If so, then that should be defining all 
macros necessary to make the headers declare extensions such as 
pthread_mutexaddr_settype (and if it isn't, then that's a bug in 
AC_USE_SYSTEM_EXTENSIONS that we need to fix).

> What is the correct approach for this situation? Should I simply define
> __USE_UNIX98 in my source code because I need the associated
> functionality? Is __USE_UNIX98 a widely used and understood macro?
> (Google searches didn't really help me understand the proper use of this
> macro.)

Generally, using AC_USE_SYSTEM_EXTENSIONS, then ensuring that your files 
include <config.h> before any system headers, should be adequate without 
you having to know whether the system spelled their extension guard as 
__USE_UNIX98, _GNU_SOURCE, __EXTENSIONS__, or some other spelling.

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org