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);
}