misc/150959: [libc] Stub pthread_once in libc should call _libc_once

[John Baldwin]

On Sunday, September 26, 2010 1:11:52 pm arundel at freebsd.org wrote:
> Old Synopsis: Stub pthread_once in libc should call _libc_once
> New Synopsis: [libc] Stub pthread_once in libc should call _libc_once
> 
> Responsible-Changed-From-To: freebsd-bugs->freebsd-threads
> Responsible-Changed-By: arundel
> Responsible-Changed-When: Sun Sep 26 17:08:28 UTC 2010
> Responsible-Changed-Why: 
> Over to maintainer(s).

As you note in the history, libstdc++ depends on this behavior, so it is not 
likely to be changed.  Possibly changing the stub to always return an error 
would be ok, except that POSIX defines no errors for pthread_once().  Note 
that this behavior also matches Solaris apparently:

(From /usr/include/c++/4.2/bits/gthr-default.h)

#if __GXX_WEAK__ && _GLIBCXX_GTHREAD_USE_WEAK

/* On Solaris 2.6 up to 9, the libc exposes a POSIX threads interface even if
   -pthreads is not specified.  The functions are dummies and most return an
   error value.  However pthread_once returns 0 without invoking the routine
   it is passed so we cannot pretend that the interface is active if -pthreads
   is not specified.  On Solaris 2.5.1, the interface is not exposed at all so
   we need to play the usual game with weak symbols.  On Solaris 10 and up, a
   working interface is always exposed.  On FreeBSD 6 and later, libc also
   exposes a dummy POSIX threads interface, similar to what Solaris 2.6 up
   to 9 does.  FreeBSD >= 700014 even provides a pthread_cancel stub in libc,
   which means the alternate __gthread_active_p below cannot be used there.  
*/

#if defined(__FreeBSD__) || (defined(__sun) && defined(__svr4__))

To be honest, I would favor libc exporting '__isthreaded' in some fashion so 
that libstdc++ could depend on that instead.  I think the symbol is already 
public so that libthr can set it.

-- 
John Baldwin