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reliable.h

#include<time.h>
#include<stdint.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<sys/uio.h>
#include<fcntl.h>
#include<unistd.h>
#include<string.h>
#include"pmseg.h"

typedef unsigned char octet_t;

struct VerwData_t
{
  time_t stamp;
  uint32_t checksum;
};

struct TVerwData_t
{
  bool dirty;
  VerwData_t pverw;
};
const int maxblocks=8;
const size_t BLOCKSIZE=4096+sizeof(VerwData_t); 
const size_t RELPAGESZ=4096;

class ReliableSegStrategy
{
public:
  
  virtual int open(char *filename)=0;
  virtual void close()=0;
  virtual int nplex()=0;
  virtual int fd(int i)=0;
  virtual off_t offset(int i,int pageno)=0;
};

class TwinblockStrategy : public ReliableSegStrategy
{
  int f;
public:
  TwinblockStrategy() {}
  int open(char *filename);
  void close();
  int nplex();
  int fd(int i);
  off_t offset(int i,int pageno);
};

class ReliableSegment: public PMSeg
{
protected:
  int fd0;
  TVerwData_t vdata[maxblocks];
  ReliableSegStrategy *strat;
public:
  ReliableSegment(ReliableSegStrategy *s);
  static uint32_t calc_checksum(octet_t *page);
  octet_t *page(int pageno) { return (octet_t *)begin()+RELPAGESZ*pageno; }
  void write_page(int pageno);
  void read_page_optimistic(int pageno);

  void read_page_reliable(int pageno);
  int open(char *filename) { return strat->open(filename); }
  
  void handle(void *page,void *addr);

  void save();
  void close() { strat->close(); }
 protected: 
  void protect(int pageno);
  void unprotect(int pageno);
};

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