boost_smart_ptr/include/boost/smart_ptr/detail/yield_k.hpp

#ifndef BOOST_SMART_PTR_DETAIL_YIELD_K_HPP_INCLUDED
#define BOOST_SMART_PTR_DETAIL_YIELD_K_HPP_INCLUDED

// MS compatible compilers support #pragma once

#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif

//
//  yield_k.hpp
//
//  Copyright (c) 2008 Peter Dimov
//
//  void yield( unsigned k );
//
//  Typical use:
//
//  for( unsigned k = 0; !try_lock(); ++k ) yield( k );
//
//  Distributed under the Boost Software License, Version 1.0.
//  See accompanying file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt
//

#include <boost/config.hpp>
#include <boost/config/pragma_message.hpp>

// BOOST_SMT_PAUSE

#if defined(_MSC_VER) && _MSC_VER >= 1310 && ( defined(_M_IX86) || defined(_M_X64) ) && !defined(__c2__)

extern "C" void _mm_pause();

#define BOOST_SMT_PAUSE _mm_pause();

#elif defined(__GNUC__) && ( defined(__i386__) || defined(__x86_64__) )

#define BOOST_SMT_PAUSE __asm__ __volatile__( "rep; nop" : : : "memory" );

#else

#define BOOST_SMT_PAUSE

#endif

//

#if defined( WIN32 ) || defined( _WIN32 ) || defined( __WIN32__ ) || defined( __CYGWIN__ )

#if defined( BOOST_USE_WINDOWS_H )
# include <windows.h>
#endif

namespace boost
{

namespace detail
{

#if !defined( BOOST_USE_WINDOWS_H )

#if defined(__clang__) && defined(__x86_64__)
// clang x64 warns that __stdcall is ignored
# define BOOST_SP_STDCALL
#else
# define BOOST_SP_STDCALL __stdcall
#endif

#if defined(__LP64__) // Cygwin 64
  extern "C" __declspec(dllimport) void BOOST_SP_STDCALL Sleep( unsigned int ms );
#else
  extern "C" __declspec(dllimport) void BOOST_SP_STDCALL Sleep( unsigned long ms );
#endif

#undef BOOST_SP_STDCALL

#endif // !defined( BOOST_USE_WINDOWS_H )

#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
  BOOST_PRAGMA_MESSAGE("Using Win32 yield_k")
#endif

inline void sp_thread_yield()
{
    Sleep( 0 );
}

inline void sp_thread_sleep()
{
    Sleep( 1 );
}

} // namespace detail

} // namespace boost

#elif defined( BOOST_HAS_PTHREADS )

#ifndef _AIX
#include <sched.h>
#else
    // AIX's sched.h defines ::var which sometimes conflicts with Lambda's var
    extern "C" int sched_yield(void);
#endif

#include <time.h>

namespace boost
{

namespace detail
{

#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
  BOOST_PRAGMA_MESSAGE("Using POSIX yield_k")
#endif

inline void sp_thread_yield()
{
    sched_yield();
}

inline void sp_thread_sleep()
{
    // g++ -Wextra warns on {} or {0}
    struct timespec rqtp = { 0, 0 };

    // POSIX says that timespec has tv_sec and tv_nsec
    // But it doesn't guarantee order or placement

    rqtp.tv_sec = 0;
    rqtp.tv_nsec = 1000;

    nanosleep( &rqtp, 0 );
}

} // namespace detail

} // namespace boost

#else

#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
  BOOST_PRAGMA_MESSAGE("Using empty yield_k")
#endif

namespace boost
{

namespace detail
{

inline void sp_thread_yield()
{
    BOOST_SMT_PAUSE
}

inline void sp_thread_sleep()
{
    BOOST_SMT_PAUSE
}

} // namespace detail

} // namespace boost

#endif

namespace boost
{

namespace detail
{

inline void yield( unsigned k ) BOOST_NOEXCEPT
{
    // Experiments show that a simple sp_thread_sleep() here is best;
    // leave a few pause instructions out of mostly superstition.
    // (These are verified to not degrade performance.)
    //
    // There seems to be no benefit from calling sp_thread_yield()
    // at any time.

    if( k < 8 )
    {
        BOOST_SMT_PAUSE
    }
    else
    {
        sp_thread_sleep();
    }
}

} // namespace detail

} // namespace boost

#endif // #ifndef BOOST_SMART_PTR_DETAIL_YIELD_K_HPP_INCLUDED