gistfile.cpp

此文件包含了在linux下实现tpr-tree索引的源代码

//--------------------------------------------------------------------
//        GiSTfile.cpp
//        ------------
//
//        GiST - Generalized Search Tree 
//        June 2001 release, Aalborg University
//        
//        This file is a revised version of a part of the original 
//        libGiST release (version  0.9beta1)     
//        Copyright (c) 1996, Regents of the University of California
//

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#ifdef UNIX
#include <unistd.h>
#else
#include <io.h>
#endif

#ifdef UNIX
#define O_BINARY 0
#endif

#include "GiSTfile.h"

//------------------------------------------------
//  The first page in the file has these "magic words"
//  and the head of the deleted page list.
//
static char magic[] = "GiST data file";

//------------------------------------------------
void
GiSTfile::Create(const char *filename)
{
  if (IsOpen()) return;

  fileHandle = open(filename, O_RDWR | O_BINARY);
  if (fileHandle >= 0)
  {
	 close(fileHandle);
    return;
  }

#ifdef UNIX
  fileHandle = open(filename,O_BINARY | O_RDWR | O_CREAT | O_TRUNC,
	      	             S_IREAD | S_IWRITE | S_IRGRP | S_IWGRP);
#else
  fileHandle = open(filename,O_BINARY | O_RDWR | O_CREAT | O_TRUNC,
	      	             S_IREAD | S_IWRITE);
#endif

  if (fileHandle < 0) return;

  SetOpen(1);

  /* Reserve page 0 */
  char *page = new char[PageSize()];
  memset(page, 0, PageSize());
  memcpy(page, magic, sizeof magic);
  Write(0, page);
//  write(fileHandle, page, PageSize());
  delete page;
  maxPage = 1;
}

//------------------------------------------------
void
GiSTfile::Open(const char *filename)
{
  char *page;

  if (IsOpen()) return;

  fileHandle = open(filename, O_RDWR | O_BINARY);

  if (fileHandle < 0) return;

  SetOpen(1);

  // Verify that the magic words are there
  page = new char[PageSize()];
  Read(0, page);
//  read(fileHandle, page, PageSize());
  if (memcmp(page, magic, sizeof(magic)))
  {
    close(fileHandle);
    SetOpen(0);
    delete page;
    return;
  }
  delete page;
  maxPage = lseek(fileHandle, 0, SEEK_END) / PageSize();  
}

//------------------------------------------------
void
GiSTfile::Close()
{
  if (!IsOpen()) return;

  close(fileHandle);
  SetOpen(0);
}

//------------------------------------------------
void
GiSTfile::Reset()
{
  if (!IsOpen()) return;

  char *page = new char[PageSize()];
  memset(page, 0, PageSize());
  memcpy(page, magic, sizeof magic);
  Write(0, page);
  delete page;
  maxPage = 1;
}

//------------------------------------------------
void
GiSTfile::Read(GiSTpage page, char *buf)
{
  if (IsOpen())
  {
    lseek(fileHandle, page * PageSize(), SEEK_SET);
    read(fileHandle, buf, PageSize());
  }
}

//------------------------------------------------
void
GiSTfile::Write(GiSTpage page, const char *buf)
{
  if (IsOpen())
  {
    lseek(fileHandle, page * PageSize(), SEEK_SET);
    write(fileHandle, buf, PageSize());
  }
}

//------------------------------------------------
GiSTpage
GiSTfile::Allocate()
{
  GiSTpage page;
  char *buf;

  if (!IsOpen()) return (0);

  // See if there's a deleted page
  buf = new char[PageSize()];
  Read(0, buf);
  memcpy(&page, buf+sizeof(magic), sizeof(GiSTpage));

  if (page)
  {
    // Reclaim this page
    Read(page, buf);
    Write(0, buf);
  }
  else
  {
      memset(buf, 0, PageSize());
      page = maxPage++;
      Write(page, buf);
//    page = lseek(fileHandle, 0, SEEK_END) / PageSize();
//    write(fileHandle, buf, PageSize());
  }
  delete buf;
  return page;
}

//------------------------------------------------
void
GiSTfile::Deallocate(GiSTpage page)
{
  char *buf;
  GiSTpage temp;

  if (!IsOpen()) return;

  // Get the old head of the list
  buf = new char[PageSize()];
  Read(0, buf);
  memcpy(&temp, buf+sizeof(magic), sizeof(GiSTpage));

  // Write the new head of the list
  memcpy(buf+sizeof(magic), &page, sizeof(GiSTpage));
  Write(0, buf);

  // In our new head, put link to old head
  memcpy(buf+sizeof(magic), &temp, sizeof(GiSTpage));
  Write(page, buf);
  delete buf;
}