Re: [boost] [thread] linux.hpp, BOOST_HAS_PTHREAD_YIELD, BOOST_HAS_SCHED_YIELD

20 Oct 2014

      Ah...ok I had to pass:

-U_GNU_SOURCE

to get things to build for a different reason. So let me check that out before you dig any further.

Thanks,
Rob
________________________________________
From: Boost  on behalf of John Maddock 
Sent: Monday, October 20, 2014 6:33 AM
To: boost@lists.boost.org
Subject: Re: [boost] [thread] linux.hpp, BOOST_HAS_PTHREAD_YIELD,       BOOST_HAS_SCHED_YIELD
...
Reposting this here since I got no response on "users" but this list seems more appropriate:
Apologies for not replying before.
...
Using boost 1.55, Ubuntu 12.04, gcc 4.6
I'm building boost on linux using the lsb sdk (4.1.8) . I was getting the failure (paraphrased):
pthread_yield not declared
in libs/thread/src/thread.cpp 513
Weird.  Fairly obviously that's a well tested combination, and normally
both BOOST_HAS_PTHREAD_YIELD and BOOST_HAS_SCHED_YIELD will get defined.

The former is a GNU extension, and I really should figure out what
define triggers it's presence (_GNU_SOURCE probably, but I need to
check).  The latter is set in posix_features.hpp via:

#     if defined(_POSIX_PRIORITY_SCHEDULING) &&
(_POSIX_PRIORITY_SCHEDULING+0 > 0)\
             || (defined(_POSIX_THREAD_PRIORITY_SCHEDULING) &&
(_POSIX_THREAD_PRIORITY_SCHEDULING+0 > 0))\
             || (defined(_XOPEN_REALTIME) && (_XOPEN_REALTIME+0 >= 0))
#        define BOOST_HAS_SCHED_YIELD
#     endif

So for whatever reason, your version of  is not signalling the
presence of this API.  Indeed the linux man pages state:

"POSIX systems on which sched_yield() is available define
_POSIX_PRIORITY_SCHEDULING in ."

which is clearly not the case here.

I'll try and see what sched.h actually does on Linux.

John.
...
The documentation for pthread_yield (http://man7.org/linux/man-pages/man3/pthread_yield.3.html) says:
This call is nonstandard, but present on several other systems. Use the standardized sched_yield(2)http://man7.org/linux/man-pages/man2/sched_yield.2.html instead.
If I change boost/config/platform/linux.hpp to define
BOOST_HAS_SCHED_YIELD
instead of
BOOST_HAS_PTHREAD_YIELD
Then sched_yield is used instead and the build finishes properly.
I'm posting this for two reasons:
1.  To help others running into the same issue
   2.  To question whether linux.hpp should be updated officially as I did above
   3.  If not, why
Thanks,
Rob Conde
_______________________________________________
Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
_______________________________________________
Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost