Subject: Re: [boost] [thread] linux.hpp, BOOST_HAS_PTHREAD_YIELD, BOOST_HAS_SCHED_YIELD
From: John Maddock (boost.regex_at_[hidden])
Date: 2014-10-20 06:33:22
> 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
So for whatever reason, your version of <unistd.h> 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 <unistd.h>."
which is clearly not the case here.
I'll try and see what sched.h actually does on Linux.
> 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
> instead of
> 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
> Rob Conde
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