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 int $maxKeys 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 string $key
  56          * @param mixed $value
  57          * @return void
  58          */
  59         public function set( $key, $value ) {
  60                 if ( array_key_exists( $key, $this->cache ) ) {
  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          * Check if a key exists
  72          *
  73          * @param string $key
  74          * @return bool
  75          */
  76         public function has( $key ) {
  77                 return array_key_exists( $key, $this->cache );
  78         }
  79
  80         /**
  81          * Get the value for a key.
  82          * This returns null if the key is not set.
  83          * If the item is already set, it will be pushed to the top of the cache.
  84          *
  85          * @param string $key
  86          * @return mixed
  87          */
  88         public function get( $key ) {
  89                 if ( array_key_exists( $key, $this->cache ) ) {
  90                         $this->ping( $key ); // push to top
  91                         return $this->cache[$key];
  92                 } else {
  93                         return null;
  94                 }
  95         }
  96
  97         /**
  98          * Clear one or several cache entries, or all cache entries
  99          *
 100          * @param string|array $keys
 101          * @return void
 102          */
 103         public function clear( $keys = null ) {
 104                 if ( $keys === null ) {
 105                         $this->cache = array();
 106                 } else {
 107                         foreach ( (array)$keys as $key ) {
 108                                 unset( $this->cache[$key] );
 109                         }
 110                 }
 111         }
 112
 113         /**
 114          * Push an entry to the top of the cache
 115          *
 116          * @param string $key
 117          */
 118         protected function ping( $key ) {
 119                 $item = $this->cache[$key];
 120                 unset( $this->cache[$key] );
 121                 $this->cache[$key] = $item;
 122         }
 123 }