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[disorder] / lib / cache.c

/*
 * This file is part of DisOrder
 * Copyright (C) 2006-2008 Richard Kettlewell
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
/** @file lib/cache.c @brief Object caching */

#include "common.h"

#include <time.h>

#include "hash.h"
#include "mem.h"
#include "log.h"
#include "syscalls.h"
#include "cache.h"

/** @brief The global cache */
static hash *h;

/** @brief One cache entry */
struct cache_entry {
  /** @brief What type of object this is */
  const struct cache_type *type;

  /** @brief Pointer to object value */
  const void *value;

  /** @brief Time that object was inserted into cache */
  time_t birth;
};

/** @brief Return true if object @p c has expired */
static int expired(const struct cache_entry *c, time_t now) {
  return now - c->birth > c->type->lifetime;
}

/** @brief Insert an object into the cache
 * @param type Pointer to object type
 * @param key Unique key
 * @param value Pointer to value
 */
void cache_put(const struct cache_type *type,
               const char *key, const void *value) {
  struct cache_entry *c;
  
  if(!h)
    h = hash_new(sizeof (struct cache_entry));
  c = xmalloc(sizeof *c);
  c->type = type;
  c->value = value;
  xtime(&c->birth);
  hash_add(h, key, c,  HASH_INSERT_OR_REPLACE);
}

/** @brief Look up an object in the cache
 * @param type Pointer to object type
 * @param key Unique key
 * @return Pointer to object value or NULL if not found
 */
const void *cache_get(const struct cache_type *type, const char *key) {
  const struct cache_entry *c;
  
  if(h
     && (c = hash_find(h, key))
     && c->type == type
     && !expired(c, xtime(0)))
    return c->value;
  else
    return 0;
}

/** @brief Call used by from cache_expire() */
static int expiry_callback(const char *key, void *value, void *u) {
  const struct cache_entry *c = value;
  const time_t *now = u;
  
  if(expired(c, *now))
    hash_remove(h, key);
  return 0;
}

/** @brief Expire the cache
 *
 * Called from time to time to expire cache entries. */
void cache_expire(void) {
  time_t now;

  if(h) {
    xtime(&now);
    hash_foreach(h, expiry_callback, &now);
  }
}

/** @brief Callback used by cache_clean() */
static int clean_callback(const char *key, void *value, void *u) {
  const struct cache_entry *c = value;
  const struct cache_type *type = u;

  if(!type || c->type == type)
    hash_remove(h, key);
  return 0;
}

/** @brief Clean the cache
 * @param type Pointer to type to clean
 *
 * Removes all entries of type @p type from the cache.
 */
void cache_clean(const struct cache_type *type) {
  if(h)
    hash_foreach(h, clean_callback, (void *)type);
}

/** @brief Report cache size
 *
 * Returns the number of objects in the cache
 */
size_t cache_count(void) {
  return h ? hash_count(h) : 0;
}

/*
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*/