char *
db_nextrec(DB *db, char *key)
{
char c, *ptr;
/* We read lock the free list so that we don't read
a record in the middle of its being deleted. */
if (readw_lock(db->idxfd, FREE_OFF, SEEK_SET, 1) < 0)
err_dump("readw_lock error");
do {
/* read next sequential index record */
if (_db_readidx(db, 0) < 0) {
ptr = NULL; /* end of index file, EOF */
goto doreturn;
}
/* check if key is all blank (empty record) */
ptr = db->idxbuf;
while ( (c = *ptr++) != 0 && c == ' ')
; /* skip until null byte or nonblank */
} while (c == 0); /* loop until a nonblank key is found */
if (key != NULL)
strcpy(key, db->idxbuf); /* return key */
ptr = _db_readdat(db); /* return pointer to data buffer */
db->cnt_nextrec++;
doreturn:
if (un_lock(db->idxfd, FREE_OFF, SEEK_SET, 1) < 0)
err_dump("un_lock error");
return(ptr);
}
/* Returning the sequential record...
Just gotta step ahead through the index file where we gotta ignore deleted records.
db_rewind() essential to be called before this function at initial stage itself */
char *db_nextrec(DB *db, char *key)
{
char c, *ptr;
/* Locking the free list where we don't actually read a record in the mid of deletion*/
if(readw_lock(db->idxfd, FREE_OFF, SEEK_SET, 1) < 0)
err_dump("error");
do
{
/* read next sequential index record */
if(_db_readidx(db, 0) < 0)
{
ptr = NULL; /* end of index file --- EOF */
goto doreturn;
}
/* Checking if the key is still blank or empty record */
ptr = db->idxbuf;
while((c = *ptr++) != 0 && c = ' ');
/* skip if it's not blank */
}
while(c == 0) /* loop untill a non-empty key is found*/
if(key != NULL)
strcpy(key, db->idxbuf); /* return key */
ptr = _db_readdat(db); /* return pointer to data buffer */
db->cnt_nextrec++;
doreturn:
if(un_lock(db->idxfd, FREE_OFF, SEEK_SET, 1) < 0)
err_dump("error");
}
/* Find specified record.
Called by db_delete(), db_fetch() and db_store() */
int _db_find(DB *db, const char *key, int writelock)
{
off_t offset, nextoffset;
/* calculate hash value for this key, then calculate byte offset of corresponding chain ptr in hash table.
*/
/* calculate offset in hash table for this key */
db->chainoff = (_db_hash(db, key) * PTR_SZ) + db->hashoff;
db->ptroff = db->chainoff;
/* here's where we lock this hash chain. It's the caller responsibility to unlock it when done.
Note that we lock and unlock only the first byte. */
if(writelock)
{
if(writew_lock(db->idxfd, db->chainoff, SEEK_SET, 1) < 0)
err_dump("error");
}
else
{
if(readw_lock(db->idxfd, db->chainoff, SEEK_SET, 1) < 0)
err_dump("error");
}
/* Get the offset in the index file of first record on the bash chain (it can be 0 too) */
offset = _db_readptr(db, db->ptroff);
while(offset!=0)
{
nextoffset = _db_readidx(db, offset);
if(strcmp(db->idxbuf, key) == 0)
break; /* found a match */
db->ptroff = offset; /* offset of this (unequal) record */
offset = nextoffset; /* next one to compare */
}
if(offset == 0)
return(-1); /* error -- record not found */
return(0); /* if not error */
}
/* Try to find a free index record and accompany data record of correct sizes.
We're only called by db_store() */
int _db_findtree(DB *db, int keylen, int datalen)
{
int rc;
off_t offset, nextoffset, saveoffset;
/* locking the free list */
if(writew_lock(db->idxfd, FREE_OFF, SEEK_SET, 1) < 0)
err_dump("error");
/* reading the free list pointer */
saveoffset = FREE_OFF;
offset = _db_readptr(db, saveoffset);
while(offset != 0)
{
nextoffset = _db_readidx(db, offset);
if(strlen(db->idxbuf) == keylen && db->datlen == datlen)
break; /* found a match */
saveoffset = offset;
offset = nextoffset;
}
if(offset == 0)
rc = -1; /* no match found */
else
{
/* Found a tree record with matching sizes.
The index record was read in by _db_readidx() above which sets db->ptrval.
Also, saveoffset points to the chain ptr that pointed to empty record on free list.
We'll be setting this chain ptr to db->ptrval, which removes empty record from free list
*/
_db_writeptr(db, saveoffset, db->ptrval);
rc = 0;
/* _db_readidx() set both db->idxoff and db->datoff.
This is used by the caller, db_store() inorder to write new index record and data record
*/
}
/* Unlocking the free list */
if(un_lock(db->idxfd, FREE_OFF, SEEK_SET, 1) < 0)
err_dump("error");
return(rc);
}
