/*-------------------------------------------------------------------------
 *
 * buf_table.c--
 *    routines for finding buffers in the buffer pool.
 *
 * Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    $Header: /cvsroot/pgsql/src/backend/storage/buffer/buf_table.c,v 1.4 1997/08/19 21:32:34 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
/*
 * OLD COMMENTS
 *
 * Data Structures:
 *
 *	Buffers are identified by their BufferTag (buf.h).  This
 * file contains routines for allocating a shmem hash table to
 * map buffer tags to buffer descriptors.
 *
 * Synchronization:
 *  
 *  All routines in this file assume buffer manager spinlock is
 *  held by their caller.
 */

#include "postgres.h"

#include "storage/bufmgr.h"
#include "storage/buf_internals.h"	/* where the declarations go */
#include "storage/shmem.h"
#include "storage/spin.h"
#include "utils/hsearch.h"

static HTAB *SharedBufHash;

typedef struct lookup { 
    BufferTag	key; 
    Buffer	id; 
} LookupEnt;

/*
 * Initialize shmem hash table for mapping buffers
 */
void
InitBufTable()
{
    HASHCTL info;
    int hash_flags;
    
    /* assume lock is held */
    
    /* BufferTag maps to Buffer */
    info.keysize = sizeof(BufferTag);
    info.datasize = sizeof(Buffer);
    info.hash = tag_hash;
    
    hash_flags = (HASH_ELEM | HASH_FUNCTION);
    
    
    SharedBufHash = (HTAB *) ShmemInitHash("Shared Buf Lookup Table",
					   NBuffers,NBuffers,
					   &info,hash_flags);
    
    if (! SharedBufHash) {
	elog(FATAL,"couldn't initialize shared buffer pool Hash Tbl");
	exit(1);
    }
    
}

BufferDesc *
BufTableLookup(BufferTag *tagPtr)
{
    LookupEnt *	result;
    bool	found;
    
    if (tagPtr->blockNum == P_NEW)
	return(NULL);
    
    result = (LookupEnt *) 
	hash_search(SharedBufHash,(char *) tagPtr,HASH_FIND,&found);
    
    if (! result){
	elog(WARN,"BufTableLookup: BufferLookup table corrupted");
	return(NULL);
    }
    if (! found) {
	return(NULL);
    }
    return(&(BufferDescriptors[result->id]));
}

/*
 * BufTableDelete
 */
bool
BufTableDelete(BufferDesc *buf)
{
    LookupEnt *	result;
    bool	found;
    
    /* buffer not initialized or has been removed from
     * table already.  BM_DELETED keeps us from removing 
     * buffer twice.
     */
    if (buf->flags & BM_DELETED) {
	return(TRUE);
    }
    
    buf->flags |= BM_DELETED;
    
    result = (LookupEnt *)
	hash_search(SharedBufHash,(char *) &(buf->tag),HASH_REMOVE,&found);
    
    if (! (result && found)) {
	elog(WARN,"BufTableDelete: BufferLookup table corrupted");    
	return(FALSE);
    }
    
    return(TRUE);
}

bool
BufTableInsert(BufferDesc *buf)
{
    LookupEnt *	result;
    bool	found;
    
    /* cannot insert it twice */
    Assert (buf->flags & BM_DELETED);
    buf->flags &= ~(BM_DELETED);
    
    result = (LookupEnt *)
	hash_search(SharedBufHash,(char *) &(buf->tag),HASH_ENTER,&found);
    
    if (! result) {
	Assert(0);
	elog(WARN,"BufTableInsert: BufferLookup table corrupted");
	return(FALSE);
    }
    /* found something else in the table ! */
    if (found) {
	Assert(0);
	elog(WARN,"BufTableInsert: BufferLookup table corrupted");
	return(FALSE);
    } 
    
    result->id = buf->buf_id;
    return(TRUE);
}

/* prints out collision stats for the buf table */
#ifdef NOT_USED
void
DBG_LookupListCheck(int nlookup)
{
    nlookup = 10;
    
    hash_stats("Shared",SharedBufHash);
}
#endif
