Net2/usr/src/lib/libc/db/btree/lrutils.c
/*-
* Copyright (c) 1990 The Regents of the University of California.
* All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Mike Olson.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)lrutils.c 5.2 (Berkeley) 2/22/91";
#endif /* LIBC_SCCS and not lint */
#include <stdlib.h>
#include <string.h>
#include "lrucache.h"
/*
* LRUGETPG -- Get a free page from the LRU cache.
*
* This routine grows the cache if necessary, finds an unused page if
* it can, and handles flushing dirty buffers to disk.
*
* One of the parameters to this routine (f) is the routine that called
* us. If we have to grow the cache, we call this routine recursively
* in order to fill the buffer. The reason for this is that we have
* two interfaces that call lrugetpg(). Lruget() fills a page from disk,
* and lrugetnew() just allocates a new (empty) page.
*
* Parameters:
* l -- LRU cache to use.
* pgno -- page number for which we want a buffer
* nread -- pointer to an int to get number of bytes read
* f -- who called us
*
* Returns:
* (char *) pointer to buffer to use, or NULL on failure.
*
* Warnings:
* The buffer returned is locked down until the user does an
* explicit lrurelease() on it.
*/
char *
lrugetpg(l, pgno, nread, f)
LRUCACHE *l;
int pgno;
int *nread;
char *(*f)();
{
CACHE_ENT *ce;
LRU_ENT *lruent;
char *buffer;
/* if we're allowed to grow the cache, do so */
if (l->lru_cursz < l->lru_csize) {
/* get a buffer */
if ((buffer = (char *) malloc((unsigned) l->lru_psize))
== (char *) NULL)
return ((char *) NULL);
/* get and LRU list entry */
if ((lruent = (LRU_ENT *) malloc((unsigned) sizeof(LRU_ENT)))
== (LRU_ENT *) NULL)
return ((char *) NULL);
lruent->l_buffer = buffer;
lruent->l_pgno = pgno;
lruent->l_flags = NULL;
/* manage spaghetti */
lruent->l_prev = (LRU_ENT *) NULL;
lruent->l_next = l->lru_head;
if (l->lru_head != (LRU_ENT *) NULL)
l->lru_head->l_prev = lruent;
l->lru_head = lruent;
if (l->lru_tail == (LRU_ENT *) NULL)
l->lru_tail = lruent;
/* add it to the hash table */
ce = lruhashput(l, pgno, lruent);
l->lru_cursz++;
} else {
lruent = l->lru_tail;
/* find the oldest unused buffer */
while (lruent != (LRU_ENT *) NULL
&& !(lruent->l_flags & F_FREE))
lruent = lruent->l_prev;
/* if no free buffer was found, we have to grow the cache */
if (lruent == (LRU_ENT *) NULL) {
if (lrugrow(l) < 0)
return ((char *) NULL);
return ((*f)((LRU) l, pgno, nread));
}
/* okay, found a free buffer -- update hash table and list */
ce = lruhashget(l, lruent->l_pgno);
if (lruhashdel(l, lruent->l_pgno) < 0)
return ((char *) NULL);
/* flush the old page to disk, if necessary */
if (lruent->l_flags & F_DIRTY)
if (lruflush(l, lruent) < 0)
return ((char *) NULL);
/* update stats, hash table, and list */
lruent->l_pgno = pgno;
lruhead(l, lruent);
ce = lruhashput(l, pgno, lruent);
buffer = lruent->l_buffer;
}
#ifdef lint
ce = ce;
#endif /* lint */
/* lock this page down */
lruent->l_flags &= ~F_FREE;
return (buffer);
}
/*
* LRUHEAD -- Move an LRU list entry to the head of the list.
*
* The head of the list is where the most recently used item goes.
*
* Parameters:
* l -- LRU cache
* lruent -- entry to move to the head of the list
*
* Returns:
* None
*
* Side Effects:
* Updates the cache's head and tail pointers as required.
*/
void
lruhead(l, lruent)
LRUCACHE *l;
LRU_ENT *lruent;
{
LRU_ENT *next;
LRU_ENT *prev;
if (l->lru_head == lruent)
return;
next = lruent->l_next;
prev = lruent->l_prev;
lruent->l_prev = (LRU_ENT *) NULL;
lruent->l_next = l->lru_head;
l->lru_head->l_prev = lruent;
l->lru_head = lruent;
prev->l_next = next;
if (next != (LRU_ENT *) NULL)
next->l_prev = prev;
if (l->lru_tail == lruent)
l->lru_tail = prev;
}
/*
* LRUGROW -- Grow the LRU cache
*
* This routine is called only if we can't satisfy a user's get() request
* using an existing buffer. We need to rebuild the hash table so that
* subsequent lookups work correctly, since the cache size is used to
* compute hash keys.
*
* Parameters:
* l -- LRU cache to grow
*
* Returns:
* Zero on success, -1 on failure
*/
int
lrugrow(l)
LRUCACHE *l;
{
int oldsz, newsz;
CACHE_ENT **new;
CACHE_ENT *ce, *nce;
int h;
int i;
oldsz = l->lru_csize;
newsz = l->lru_csize + 1;
/* get a new hash table */
if ((new = (CACHE_ENT **) malloc((unsigned)newsz * sizeof(CACHE_ENT *)))
== (CACHE_ENT **) NULL)
return (-1);
/* build the new hash table */
bzero((char *) new, (size_t) (newsz * sizeof(CACHE_ENT *)));
for (i = oldsz; --i >= 0; ) {
for (ce = l->lru_cache[i]; ce != (CACHE_ENT *) NULL; ) {
nce = ce->c_chain;
h = ce->c_pgno % newsz;
ce->c_chain = new[h];
new[h] = ce;
ce = nce;
}
}
/* get rid of the old hash table, and update the cache */
free ((char *) (l->lru_cache));
l->lru_cache = new;
l->lru_csize = newsz;
return (0);
}