bufhash.c

linux 下用c++ 开发的一个小型数据库系统

#include <memory.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <fcntl.h>
#include <iostream>
#include <stdio.h>
#include "page.h"
#include "buf.h"

// buffer pool hash table implementation

int BufHashTbl::hash(const File* file, const int pageNo)
{
  int tmp, value;

  tmp = (int)file;  // cast of pointer to the file object to an integer
  value = (tmp + pageNo) % HTSIZE;

  return value;
}


BufHashTbl::BufHashTbl(int htSize)
{
  HTSIZE = htSize;

  // allocate an array of pointers to hashBuckets

  ht = new hashBucket* [htSize];

  for(int i=0; i < HTSIZE; i++)
    ht[i] = NULL;
}


BufHashTbl::~BufHashTbl()
{
  for(int i = 0; i < HTSIZE; i++) {
    hashBucket* tmpBuf = ht[i];
    while (ht[i]) {
      tmpBuf = ht[i];
      ht[i] = ht[i]->next;
      delete tmpBuf;
    }
  }
  delete [] ht;
}


//---------------------------------------------------------------
// insert entry into hash table mapping (file,pageNo) to frameNo;
// returns OK if OK, HASHTBLERROR if an error occurred
//---------------------------------------------------------------
Status BufHashTbl::insert(const File *file, const int pageNo, const int frameNo)
{
  int index ;
  hashBucket *mybk = NULL ;

  index = hash(file,pageNo) ;
  mybk = ht[index] ;

  while(mybk != NULL){
    if((mybk->file == file) && (mybk->pageNo == pageNo)) return HASHTBLERROR ;
    mybk = mybk->next ;
  }

  mybk = new hashBucket ; 

  if(mybk != NULL){
    mybk->file =(File *)file ;
    mybk->pageNo = pageNo ;
    mybk->frameNo = frameNo ;
    mybk->next = ht[index] ;
    ht[index] = mybk ;

    return OK ;
  }

  return HASHTBLERROR ;
}


//-------------------------------------------------------------------	     
// Check if (file,pageNo) is currently in the buffer pool (ie. in
// the hash table).  If so, return corresponding frameNo. else return 
// HASHNOTFOUND
//-------------------------------------------------------------------

Status BufHashTbl::lookup(const File* file, const int pageNo, int& frameNo) 
{
  int index ;
  hashBucket * mybk = NULL ;
  
  index = hash(file,pageNo) ;
  mybk = ht[index] ;

  while(mybk != NULL){
//    cout<<"look "<<mybk->file<<" "<<pageNo<<endl ;
    if((mybk->file == file) && (mybk->pageNo == pageNo)){
      frameNo = mybk->frameNo ;
      return OK ;
    }

    mybk = mybk->next ;
  }

  return HASHNOTFOUND ;
}



//-------------------------------------------------------------------
// delete entry (file,pageNo) from hash table. REturn OK if page was
// found.  Else return HASHTBLERROR
//-------------------------------------------------------------------

Status BufHashTbl::remove(const File* file, const int pageNo) 
{
  int index ;
  hashBucket * mybk = NULL ;
  hashBucket * mybk1 = NULL ;

  index = hash(file, pageNo) ;
  mybk1 = mybk = ht[index] ;

  while(mybk){
    if ((mybk->file == file) && (mybk->pageNo == pageNo)){
      if (ht[index] == mybk) ht[index] = mybk->next ;
      else mybk1->next = mybk->next ;
      mybk->file = NULL ;
      delete mybk ;

      return OK ;
    }
    else{
      mybk1 = mybk ;
      mybk = mybk->next ;
    }
  }

 return HASHTBLERROR ;
}