C:/rwlock/SimpleRWLock.h

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//
// http://discuss.microsoft.com/SCRIPTS/WA-MSD.EXE?A2=ind0009A&L=ATL&P=R6194&D=0&I=-3
// Posted by Pavel Lebedinsky <pll@INFRA2000.COM>
//
#ifndef __Simple_LOCK_H_Included__
#define __Simple_LOCK_H_Included__

//#include <Windows.h>
#include "atomic_util.h"
#include "system_abstraction.h"

class SimpleRWLock
{
    volatile int m_nReaders;
    volatile int m_nWriters;

public:
    SimpleRWLock()
    {
        m_nReaders = 0;
        m_nWriters = 0;
    }

        static const char *name() { return "Simple_Lock"; }

        void enter_read(void)
    {
        for (;;)
        {
            atomic_inc(&m_nReaders);
            if (m_nWriters == 0) break;
            atomic_dec(&m_nReaders);
            thread_yield();
        }
    }

        void enter_write(void)
    {
        for (;;)
        {
            if (atomic_cmpexch_return(&m_nWriters, 1, 0) == 0)
            {
                while (m_nReaders != 0) thread_yield();
                break;
            }
            thread_yield();
        }
    }

    void leave_read(void)
    {
        atomic_dec(&m_nReaders);
    }

    void leave_write(void)
    {
        atomic_dec(&m_nWriters);
    }
};
#endif // __Simple_LOCK_H_Included__

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