[PATCH] revised fix for nanosleep check in GLIBCXX_ENABLE_LIBSTDCXX_TIME for darwin

[Jack Howarth]

On Tue, Oct 09, 2012 at 09:21:25AM +0100, Jonathan Wakely wrote:
> On 9 October 2012 01:39, Jack Howarth wrote:
> >    The --enable-libstdcxx-time=yes configure option fails to validate the
> > presence of a usable nanosleep() call on darwin due to its use of pre-2008
> > POSIX timers. As both nanosleep() and sched_yield() have always been available
> > on darwin, the attached patch simply defines _GLIBCXX_USE_NANOSLEEP and
> > _GLIBCXX_USE_SCHED_YIELD in config/os/bsd/darwin/os_defines.h. This also has
> > the advantage of effectively making --enable-libstdcxx-time=yes the default
> > on darwin. Regression tested on x86_64-apple-darwin12.
> >    Okay for gcc trunk as well as gcc-4_7-branch/gcc-4_6-branch/gcc-4_5-branch?
> 
> The 4.5 branch is closed, so definitely not alright there.
> 
> I don't like the sched_yield macro being set there because it's
> detected correctly by configure anyway, but I'm not going to labour
> that point any more.

Since we are defining _GLIBCXX_USE_NANOSLEEP in os_defines.h and effectively
implementing half of the behavior of --enable-libstdcxx-time=yes, it seemed
odd to not complete the process and define _GLIBCXX_USE_SCHED_YIELD as well.
The usage is not as straight-forward as many other configure options 
(especially in light of the absence of rt timer support on darwin).

> 
> OK for trunk, it's not a regression so I'm not sure about the
> branches. If it doesn't cause problems on the trunk we can decide
> whether to apply it to the 4.7 branch later.

I guess the question is which branches have enough C++11 standard support to
make the change meaningful to the end user.