[Boost-users] [Smart pointers] BOOST_SP_HAS_SYNC undefined on ARM

Subject: [Boost-users] [Smart pointers] BOOST_SP_HAS_SYNC undefined on ARM
From: Vaclav Barta (vbar_at_[hidden])
Date: 2013-03-14 03:07:13

Hi,

I've been looking at some traces of our Android app (which is mostly 
native and extensively uses boost) and was surprised to find it uses 
spinlocks around the reference count of boost::shared_ptr. So I've 
checked the boost sources and found 
boost/smart_ptr/detail/atomic_count.hpp choosing the implementation 
depending on platform and other #defines, of which BOOST_SP_HAS_SYNC 
sounded like it should be turned on (Google recommends using gcc 
__sync_* intrinsics on Android). But, 
boost/smart_ptr/detail/sp_has_sync.hpp requires either 
__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 (which the Google cross-compiler 
apparently doesn't have), or (for recent gcc)

#define BOOST_SP_HAS_SYNC

#if defined( __arm__ )  || defined( __armel__ )
#undef BOOST_SP_HAS_SYNC
#endif

Why not use the intrinsics on ARM? Are they broken? For all ARM 
variants, or just some (ideally some old ones - I cound ignore them 
then)? Or are the intrinsics' semantics incompatible with the way boost 
atomic count needs?

     Bye
         Vasek
--
http://www.mangrove.cz/