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  */
  32 class MapCacheLRU {
  33         /** @var Array */
  34         protected $cache = array(); // (key => value)
  35
  36         protected $maxCacheKeys; // integer; max entries
  37
  38         /**
  39          * @param $maxKeys integer Maximum number of entries allowed (min 1).
  40          * @throws MWException When $maxCacheKeys is not an int or =< 0.
  41          */
  42         public function __construct( $maxKeys ) {
  43                 if ( !is_int( $maxKeys ) || $maxKeys < 1 ) {
  44                         throw new MWException( __METHOD__ . " must be given an integer and >= 1" );
  45                 }
  46                 $this->maxCacheKeys = $maxKeys;
  47         }
  48
  49         /**
  50          * Set a key/value pair.
  51          * This will prune the cache if it gets too large based on LRU.
  52          * If the item is already set, it will be pushed to the top of the cache.
  53          *
  54          * @param $key string
  55          * @param $value mixed
  56          * @return void
  57          */
  58         public function set( $key, $value ) {
  59                 if ( isset( $this->cache[$key] ) ) {
  60                         $this->ping( $key ); // push to top
  61                 } elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
  62                         reset( $this->cache );
  63                         $evictKey = key( $this->cache );
  64                         unset( $this->cache[$evictKey] );
  65                 }
  66                 $this->cache[$key] = $value;
  67         }
  68
  69         /**
  70          * Check if a key exists
  71          *
  72          * @param $key string
  73          * @return bool
  74          */
  75         public function has( $key ) {
  76                 return isset( $this->cache[$key] );
  77         }
  78
  79         /**
  80          * Get the value for a key.
  81          * This returns null if the key is not set.
  82          * If the item is already set, it will be pushed to the top of the cache.
  83          *
  84          * @param $key string
  85          * @return mixed
  86          */
  87         public function get( $key ) {
  88                 if ( isset( $this->cache[$key] ) ) {
  89                         $this->ping( $key ); // push to top
  90                         return $this->cache[$key];
  91                 } else {
  92                         return null;
  93                 }
  94         }
  95
  96         /**
  97          * Clear one or several cache entries, or all cache entries
  98          *
  99          * @param $keys string|Array
 100          * @return void
 101          */
 102         public function clear( $keys = null ) {
 103                 if ( $keys === null ) {
 104                         $this->cache = array();
 105                 } else {
 106                         foreach ( (array)$keys as $key ) {
 107                                 unset( $this->cache[$key] );
 108                         }
 109                 }
 110         }
 111
 112         /**
 113          * Push an entry to the top of the cache
 114          *
 115          * @param $key string
 116          */
 117         protected function ping( $key ) {
 118                 $item = $this->cache[$key];
 119                 unset( $this->cache[$key] );
 120                 $this->cache[$key] = $item;
 121         }
 122 }