[boost] platform specific structures

From: Matt Hurd (matt.hurd_at_[hidden])
Date: 2004-09-19 20:06:00

I'm interested in getting something like "needs_lock" below into the
normal traits, perhaps as part of boost thread.  It informs you
whether of not an operation on such a contiguous block needs a lock to
be atomic.

For example, on ia32 32 bit aligned ops are atomic, on ia64 it is 64
bit.  doubles on ia32 need locking to be atomic, on ia64 they don't. 
sizeof(void*) works generically for these two platforms as is included
in the code below.  A default, safety first implementation might
return true always for needs lock, or perhaps, true for all sizeof's
greater than a byte.

"Ifdef" hell for platforms can read to readability problems and big
config.hpp equivalents.  An alternative is to redirect headers to
generic, where possible, or platform specific headers, where
necessary, but this may lead to a bit of a maintenance nightmare due
to supporting similar code for different platforms even though the
code is typically much more readable.  Another often intertwined
approach is to include a platform independent api/function layer that
is then used by the library, e.g. ACE's os.h.

Any suggestions on best practice for this?

Regards,

Matt Hurd
matthurd_at_[hidden]
www.hurd.com.au

/*_____________________________________________________________________

            created:           2004-6-7   16:20
            filename:          needs_lock.hpp
            author:            Matt Hurd
_______________________________________________________________________*/

#ifndef NEEDS_LOCK_HPP_200467
#define NEEDS_LOCK_HPP_200467

#include <boost/type_traits.hpp>

#include "boost/type_traits/is_integral.hpp"
#include "boost/type_traits/is_float.hpp"
#include "boost/type_traits/detail/ice_or.hpp"
#include "boost/config.hpp"

// should be the last #include
#include "boost/type_traits/detail/bool_trait_def.hpp"

    namespace boost {

        namespace detail {

            template< typename T >
            struct needs_lock_impl
            { 
                BOOST_STATIC_CONSTANT(bool, value = (sizeof(T) >
sizeof( void *)) );
            };

        } // namespace detail

        BOOST_TT_AUX_BOOL_TRAIT_DEF1(needs_lock,T,::boost::detail::needs_lock_impl<T>::value)

    } // namespace boost

#include "boost/type_traits/detail/bool_trait_undef.hpp"

#endif