includes/cache/MapCacheLRU.php

   1 <?php
   2 /**
   3  * Per-process memory cache for storing items.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Cache
  22  */
  23
  24 /**
  25  * Handles a simple LRU key/value map with a maximum number of entries
  26  *
  27  * Use ProcessCacheLRU if hierarchical purging is needed or objects can become stale
  28  *
  29  * @see ProcessCacheLRU
  30  * @ingroup Cache
  31  * @since 1.23
  32  */
  33 class MapCacheLRU {
  34         /** @var Array */
  35         protected $cache = array(); // (key => value)
  36
  37         protected $maxCacheKeys; // integer; max entries
  38
  39         /**
  40          * @param $maxKeys integer Maximum number of entries allowed (min 1).
  41          * @throws MWException When $maxCacheKeys is not an int or =< 0.
  42          */
  43         public function __construct( $maxKeys ) {
  44                 if ( !is_int( $maxKeys ) || $maxKeys < 1 ) {
  45                         throw new MWException( __METHOD__ . " must be given an integer and >= 1" );
  46                 }
  47                 $this->maxCacheKeys = $maxKeys;
  48         }
  49
  50         /**
  51          * Set a key/value pair.
  52          * This will prune the cache if it gets too large based on LRU.
  53          * If the item is already set, it will be pushed to the top of the cache.
  54          *
  55          * @param $key string
  56          * @param $value mixed
  57          * @return void
  58          */
  59         public function set( $key, $value ) {
  60                 if ( isset( $this->cache[$key] ) ) {
  61                         $this->ping( $key ); // push to top
  62                 } elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
  63                         reset( $this->cache );
  64                         $evictKey = key( $this->cache );
  65                         unset( $this->cache[$evictKey] );
  66                 }
  67                 $this->cache[$key] = $value;
  68         }
  69
  70         /**
  71          * Get the value for a key.
  72          * This returns null if the key is not set.
  73          * If the item is already set, it will be pushed to the top of the cache.
  74          *
  75          * @param $key string
  76          * @param $prop string
  77          * @return mixed
  78          */
  79         public function get( $key ) {
  80                 if ( isset( $this->cache[$key] ) ) {
  81                         $this->ping( $key ); // push to top
  82                         return $this->cache[$key];
  83                 } else {
  84                         return null;
  85                 }
  86         }
  87
  88         /**
  89          * Clear one or several cache entries, or all cache entries
  90          *
  91          * @param $keys string|Array
  92          * @return void
  93          */
  94         public function clear( $keys = null ) {
  95                 if ( $keys === null ) {
  96                         $this->cache = array();
  97                 } else {
  98                         foreach ( (array)$keys as $key ) {
  99                                 unset( $this->cache[$key] );
 100                         }
 101                 }
 102         }
 103
 104         /**
 105          * Push an entry to the top of the cache
 106          *
 107          * @param $key string
 108          */
 109         protected function ping( $key ) {
 110                 $item = $this->cache[$key];
 111                 unset( $this->cache[$key] );
 112                 $this->cache[$key] = $item;
 113         }
 114 }