includes/libs/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 use Wikimedia\Assert\Assert;
  24
  25 /**
  26  * Handles a simple LRU key/value map with a maximum number of entries
  27  *
  28  * Use ProcessCacheLRU if hierarchical purging is needed or objects can become stale
  29  *
  30  * @see ProcessCacheLRU
  31  * @ingroup Cache
  32  * @since 1.23
  33  */
  34 class MapCacheLRU {
  35         /** @var array */
  36         protected $cache = []; // (key => value)
  37
  38         protected $maxCacheKeys; // integer; max entries
  39
  40         /**
  41          * @param int $maxKeys Maximum number of entries allowed (min 1).
  42          * @throws Exception When $maxCacheKeys is not an int or not above zero.
  43          */
  44         public function __construct( $maxKeys ) {
  45                 Assert::parameterType( 'integer', $maxKeys, '$maxKeys' );
  46                 Assert::parameter( $maxKeys > 0, '$maxKeys', 'must be above zero' );
  47
  48                 $this->maxCacheKeys = $maxKeys;
  49         }
  50
  51         /**
  52          * Set a key/value pair.
  53          * This will prune the cache if it gets too large based on LRU.
  54          * If the item is already set, it will be pushed to the top of the cache.
  55          *
  56          * @param string $key
  57          * @param mixed $value
  58          * @return void
  59          */
  60         public function set( $key, $value ) {
  61                 if ( array_key_exists( $key, $this->cache ) ) {
  62                         $this->ping( $key );
  63                 } elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
  64                         reset( $this->cache );
  65                         $evictKey = key( $this->cache );
  66                         unset( $this->cache[$evictKey] );
  67                 }
  68                 $this->cache[$key] = $value;
  69         }
  70
  71         /**
  72          * Check if a key exists
  73          *
  74          * @param string $key
  75          * @return bool
  76          */
  77         public function has( $key ) {
  78                 return array_key_exists( $key, $this->cache );
  79         }
  80
  81         /**
  82          * Get the value for a key.
  83          * This returns null if the key is not set.
  84          * If the item is already set, it will be pushed to the top of the cache.
  85          *
  86          * @param string $key
  87          * @return mixed Returns null if the key was not found
  88          */
  89         public function get( $key ) {
  90                 if ( !array_key_exists( $key, $this->cache ) ) {
  91                         return null;
  92                 }
  93
  94                 $this->ping( $key );
  95
  96                 return $this->cache[$key];
  97         }
  98
  99         /**
 100          * @return array
 101          * @since 1.25
 102          */
 103         public function getAllKeys() {
 104                 return array_keys( $this->cache );
 105         }
 106
 107         /**
 108          * Get an item with the given key, producing and setting it if not found.
 109          *
 110          * If the callback returns false, then nothing is stored.
 111          *
 112          * @since 1.28
 113          * @param string $key
 114          * @param callable $callback Callback that will produce the value
 115          * @return mixed The cached value if found or the result of $callback otherwise
 116          */
 117         public function getWithSetCallback( $key, callable $callback ) {
 118                 if ( $this->has( $key ) ) {
 119                         $value = $this->get( $key );
 120                 } else {
 121                         $value = call_user_func( $callback );
 122                         if ( $value !== false ) {
 123                                 $this->set( $key, $value );
 124                         }
 125                 }
 126
 127                 return $value;
 128         }
 129
 130         /**
 131          * Clear one or several cache entries, or all cache entries
 132          *
 133          * @param string|array $keys
 134          * @return void
 135          */
 136         public function clear( $keys = null ) {
 137                 if ( $keys === null ) {
 138                         $this->cache = [];
 139                 } else {
 140                         foreach ( (array)$keys as $key ) {
 141                                 unset( $this->cache[$key] );
 142                         }
 143                 }
 144         }
 145
 146         /**
 147          * Push an entry to the top of the cache
 148          *
 149          * @param string $key
 150          */
 151         protected function ping( $key ) {
 152                 $item = $this->cache[$key];
 153                 unset( $this->cache[$key] );
 154                 $this->cache[$key] = $item;
 155         }
 156 }