147 lines
4.6 KiB
C
147 lines
4.6 KiB
C
/* cache.c -- routines to implement a generic, list(3)-based cache package.
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*
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* Last edited: Tue Jul 28 15:41:47 1992 by bcs (Bradley C. Spatz) on wasp
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*
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* Copyright (C) 1992, Bradley C. Spatz, bcs@ufl.edu
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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*
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* We define the following routines here:
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*
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* CACHE *cache_init(max_elements)
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* char *cache_enter(cache, data, bytes, removed)
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* char *cache_check(cache, data, match)
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* void cache_free(cache, dealloc)
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*
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* for
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*
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* CACHE *cache;
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* char *data;
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* int max_elements, max_size, bytes;
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* char **removed;
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* int match(data, curr)
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* char *data;
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* char *curr;
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* void dealloc(data)
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* char *data;
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*
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* We base this package on the list(3) package.
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*
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* Keep a data structure that is essentially a list. We'll add new
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* elements to the front of the list and remove old elements from the end
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* of the list. We'll optimize searches for MRU (Most Recently Used) and
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* we'll dispose of elements when we need space by using LRU. Finally,
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* we'll always promote the element on a hit to the front of the list.
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*
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* We'll allow the user to control the size of the cache in terms of
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* cache elements. This limit will be determined at cache creation.
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*/
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static char brag[] = "$$Version: cache " "PACKAGE_VERSION" " Copyright (C) 1992 Bradley C. Spatz";
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#include <stdio.h>
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#include <stdlib.h>
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#include "cache.h"
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CACHE *cache_init(int max_elements)
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{
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CACHE *new_cache;
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/* Allocate, initialize, and return a new cache. Return NULL if
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* the malloc or list initialization fails.
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*/
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if ((new_cache = (CACHE *) malloc(sizeof(CACHE))) == NULL) {
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return(NULL);
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}
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new_cache->max_elements = max_elements;
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if ((new_cache->list = list_init()) == NULL) {
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/* The list creation fragged, so release the cache descriptor. */
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free(new_cache);
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return(NULL);
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}
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return(new_cache);
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}
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void *cache_enter(CACHE *cache, void *data, int bytes, void **removed)
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{
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char *new_element;
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/* Add a new element to the front of our list. This is easy, because
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* we're using the list(3) package; our intentions exactly.
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* Try and add the new element. If that succeeds, then check for a
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* full cache. If full, remove the element at the rear of the list.
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* We return a pointer to the newly inserted element or NULL if the
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* insert failed. We also return a pointer to the removed element
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* if we did indeed remove one.
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*/
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*removed = NULL;
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new_element = list_insert_before(cache->list, data, bytes);
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if (new_element != NULL) {
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if (list_size(cache->list) > cache->max_elements) {
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*removed = (char *) list_remove_rear(cache->list);
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}
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}
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return(new_element);
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}
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void *cache_check(CACHE *cache, void *data, cache_match_func_t match)
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{
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char *found;
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/* Check for an empty cache. */
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if (list_size(cache->list) == 0) {
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return(NULL);
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}
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/* Ok. Search the list for the element, starting from the front
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* of our list. If the traversal finds the element, then promote it to
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* the front if it's not already there, and return a pointer to the element.
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* Otherwise, return NULL. In either case, make sure to reset the
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* current element pointer back to the front of the list.
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*/
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if (list_traverse(cache->list, data, match,
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(LIST_FRNT | LIST_FORW | LIST_ALTR)) == LIST_OK) {
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/* We found what we're looking for. */
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if (list_curr(cache->list) != list_front(cache->list)) {
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fprintf(stderr, "cache_check: moving found to front.\n");
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found = (char *) list_remove_curr(cache->list);
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list_mvfront(cache->list);
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list_insert_before(cache->list, found, 0);
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return(found);
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}
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else {
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return(list_front(cache->list));
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}
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}
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else {
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/* We did not find the element. */
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list_mvfront(cache->list);
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return(NULL);
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}
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}
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void cache_free(CACHE *cache, cache_dealloc_func_t dealloc)
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{
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/* First free up the list, and then the cache descriptor. */
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list_free(cache->list, dealloc);
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free(cache);
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}
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