MirrorBufferSet.h

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//=============================================================================
//  $Id: MirrorBufferSet.h,v 1.1 2006/06/12 20:21:44 gallen Exp $
//-----------------------------------------------------------------------------
//  A set of "mirrored" buffers
//=============================================================================


#ifndef MirrorBufferSet_h
#define MirrorBufferSet_h
#pragma once
#include "common_priv.h"

//-----------------------------------------------------------------------------
//  Implementation notes:
//
//  +------------------+------------+------------------+------------+
//  |    bufferSize    | mirrorSize |    bufferSize    | mirrorSize | ...
//  +------------------+------------+------------------+------------+
//
//  Each buffer has its first mirrorSize bytes mirrored by the VM system.
//  There are numBuffers contiguous buffers.
//  bufferSize and mirrorSize are multiples of the VM page size.
//  mirrorSize <= bufferSize
//-----------------------------------------------------------------------------


class MirrorBufferSet {
  public:
    typedef unsigned long ulong;

    MirrorBufferSet(ulong bufferSz, ulong mirrorSz, int nBuffers = 1);
   ~MirrorBufferSet(void);

    ulong BufferSize(void) const { return bufferSize; }
    ulong MirrorSize(void) const { return mirrorSize; }
    ulong NumBuffers(void) const { return numBuffers; }

    enum { eNotSupported=0, eSupportedPosixShm, eSupportedTmpFile };

    static int Supported(void);
    static ulong PageSize(void);

    operator void* (void) const { return bufferBase; }

  protected:
    int GetFileDescriptor(void);

    void*   bufferBase;
    ulong   bufferSize;
    ulong   mirrorSize;
    int     numBuffers;
    char    fileName[112];
};


#endif