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Smart Pointers to boost your code

, 27 Sep 2004
A beginner's introduction to the smart pointers provided by the boost library.
#ifndef BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED
#define BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED

// MS compatible compilers support #pragma once

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

//
//  boost/detail/lwm_win32.hpp
//
//  Copyright (c) 2002, 2003 Peter Dimov
//
//  Permission to copy, use, modify, sell and distribute this software
//  is granted provided this copyright notice appears in all copies.
//  This software is provided "as is" without express or implied
//  warranty, and with no claim as to its suitability for any purpose.
//

#ifdef BOOST_USE_WINDOWS_H
#  include <windows.h>
#endif

#ifdef __BORLANDC__
# pragma warn -8027     // Functions containing while are not expanded inline
#endif

namespace boost
{

namespace detail
{

#ifndef BOOST_USE_WINDOWS_H

#ifdef _WIN64

// Intel 6.0 on Win64 version, posted by Tim Fenders to [boost-users]

extern "C" long_type __cdecl _InterlockedExchange(long volatile *, long);

#pragma intrinsic(_InterlockedExchange)

inline long InterlockedExchange(long volatile* lp, long l)
{
    return _InterlockedExchange(lp, l);
}

#else  // _WIN64

extern "C" __declspec(dllimport) long __stdcall InterlockedExchange(long volatile *, long);

#endif // _WIN64

extern "C" __declspec(dllimport) void __stdcall Sleep(unsigned long);

#endif // #ifndef BOOST_USE_WINDOWS_H

class lightweight_mutex
{
private:

    long l_;

    lightweight_mutex(lightweight_mutex const &);
    lightweight_mutex & operator=(lightweight_mutex const &);

public:

    lightweight_mutex(): l_(0)
    {
    }

    class scoped_lock;
    friend class scoped_lock;

    class scoped_lock
    {
    private:

        lightweight_mutex & m_;

        scoped_lock(scoped_lock const &);
        scoped_lock & operator=(scoped_lock const &);

    public:

        explicit scoped_lock(lightweight_mutex & m): m_(m)
        {
            while( InterlockedExchange(&m_.l_, 1) )
            {
                // Note: changed to Sleep(1) from Sleep(0).
                // According to MSDN, Sleep(0) will never yield
                // to a lower-priority thread, whereas Sleep(1)
                // will. Performance seems not to be affected.

                Sleep(1);
            }
        }

        ~scoped_lock()
        {
            InterlockedExchange(&m_.l_, 0);

            // Note: adding a yield here will make
            // the spinlock more fair and will increase the overall
            // performance of some applications substantially in
            // high contention situations, but will penalize the
            // low contention / single thread case up to 5x
        }
    };
};

} // namespace detail

} // namespace boost

#ifdef __BORLANDC__
# pragma warn .8027     // Functions containing while are not expanded inline
#endif

#endif // #ifndef BOOST_DETAIL_LWM_WIN32_HPP_INCLUDED

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About the Author

peterchen
Klippel
Germany Germany
Peter is tired of being called "Mr. Chen", even so certain individuals insist on it. No, he's not chinese.
 
Peter has seen lots of boxes you youngsters wouldn't even accept as calculators. He is proud of having visited the insides of a 16 Bit Machine.
 
In his spare time he ponders new ways of turning groceries into biohazards, or tries to coax South American officials to add some stamps to his passport.
 
Beyond these trivialities Peter works for Klippel[^], a small german company that wants to make mankind happier by selling them novel loudspeaker measurement equipment.
 

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