C:/rwlock/evg_rwlock_2.h

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/* ****************************************************************************
 * Owner:               Evgeniy Makeev
 * Created by:  Evgeniy Makeev
 * ****************************************************************************
 */
#ifndef __EVG_RW_LOCK_2_H_Included__
#define __EVG_RW_LOCK_2_H_Included__ 

#include "atomic_util.h"
#include "system_abstraction.h"

/*---------------------------------*/
/* Written by Evgeniy Makeev, 2005 */
/*---------------------------------*/
//
// Multiple readers - one writer interface class.
// Implements multiple readers one writer mechanism.
// Optimizes readers speed, provides fast readers
// synchronization when no writers are waiting.
// Useful when data is needed to be written/changed
// only occasionally but it is read often by multiple
// threads.
// 

class EvgRWLock2
{
        volatile int readers;
//
// Can be overwritten with a system specific yield thread
// or sleep implementation
//
        inline void yield()
        {
                thread_yield();
        }

public:
        static const char *name() { return "Evgeniy's RW Lock 2"; }

        EvgRWLock2() : rwdata(0L) {}
//
// Must be called at the beginning of any read/data access.
//
        inline void enter_read(void)
        {
                if(atomic_inc_return(&rwdata) & 0xFFFF8000)
                        for(;;)
                        {
                                if(atomic_dec_return(&rwdata) & 0xFFFF8000) yield();
                                if((atomic_inc_return(&rwdata) & 0xFFFF8000)==0) break;
                        }
        }
//
// Must be called at the end of any read/data access.
//
        inline void leave_read(void)
        {
                atomic_dec(&rwdata);
        }
//
// Must be called at the beginning of a write operation
//
        inline void enter_write(void)
        {
                if(atomic_cmpexch_return(&rwdata, 0x00008000, 0))
                {
                                atomic_add(&rwdata, 0x00010000);
                                for(;;)
                                {
                                        if(atomic_cmpexch_return_w((short *)&rwdata, (short)0x8000, (short)0) == 0) 
                                        {
                                                atomic_add(&rwdata, -0x00010000);
                                                break;
                                        }
                                        yield();
                                }
                }
        }       
//
// Must be called at the end of a write operation
//
        inline void leave_write(void)
        {
                atomic_and(&rwdata, ~0x00008000);
        }
};

#endif // __EVG_RW_LOCK_2_H_Included__

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