SpinLock.h

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//==============================================================================================
//  FILENAME    :   SpinLock.h
//  AUTHOR      :   vovechkin
//  CREATION    :   2004-10-22
//  Copyright (C) MicroStrategy Incorporated 2004
//==============================================================================================
#ifndef MBase_SpinLock_h
#define MBase_SpinLock_h

#include "../Base/Atomic.h"

#if defined(linux)
#include <sched.h> // for ::sched_yield
#endif
#include "../../PDCHeader/PDCunistd.h" // for ::sleep

namespace MBase
{
    class SpinLock
    {
    public:

        SpinLock()
        {
            // 2004-10-22 vovechkin:
            // it is important that the constructor be empty,
            // because SpinLock is used by ModuleMainPtr, which
            // has to have an empty C++ constructor.
        }

        class SmartLock
        {
        public:

            SmartLock(SpinLock& irSpinLock):
                mrSpinLock(irSpinLock),
                mIsLocked(true)
            {
                mrSpinLock.Lock();
            }

            ~SmartLock() throw()
            {
                if (mIsLocked)
                {
                    mrSpinLock.Unlock();
                }
            }

            void Unlock() throw()
            {
                if (mIsLocked)
                {
                    mrSpinLock.Unlock();
                    mIsLocked = false;
                }
            }

        private:

            SpinLock& mrSpinLock;
            bool mIsLocked;
        };

    private:

        friend class SmartLock;

        void Lock() throw()
        {
            // 2004-10-22 vovechkin
            // since the constructor is empty (on purpose)
            // we use 0x12345678 to differentiate from any
            // other (uninitialized) value.
            while (MBase::AtomicExchange(mValue, 0x12345678) == 0x12345678)
            {
                // 2004-10-23 vovechkin
                // it would be better to use MBase::YieldToAnotherThread
                // however, that would bring a link-dependency on Base,
                // which many projects do not have.
#ifdef WIN32
                ::Sleep(0);
#elif defined(linux)
                // on Linux, sleep(0) does not do anything
                ::sched_yield();
#else
                ::sleep(0);
#endif
            }
        }

        void Unlock() throw()
        {
            MBase::AtomicExchange(mValue, 0);
        }

    private:

        long mValue;
    };
}

#endif // MBase_SpinLock_h