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 ( $this->has( $key ) ) {
  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                 if ( !is_int( $key ) && !is_string( $key ) ) {
  79                         throw new UnexpectedValueException(
  80                                 __METHOD__ . ' called with invalid key. Must be string or integer.' );
  81                 }
  82                 return array_key_exists( $key, $this->cache );
  83         }
  84
  85         /**
  86          * Get the value for a key.
  87          * This returns null if the key is not set.
  88          * If the item is already set, it will be pushed to the top of the cache.
  89          *
  90          * @param string $key
  91          * @return mixed Returns null if the key was not found
  92          */
  93         public function get( $key ) {
  94                 if ( !$this->has( $key ) ) {
  95                         return null;
  96                 }
  97
  98                 $this->ping( $key );
  99
 100                 return $this->cache[$key];
 101         }
 102
 103         /**
 104          * @return array
 105          * @since 1.25
 106          */
 107         public function getAllKeys() {
 108                 return array_keys( $this->cache );
 109         }
 110
 111         /**
 112          * Get an item with the given key, producing and setting it if not found.
 113          *
 114          * If the callback returns false, then nothing is stored.
 115          *
 116          * @since 1.28
 117          * @param string $key
 118          * @param callable $callback Callback that will produce the value
 119          * @return mixed The cached value if found or the result of $callback otherwise
 120          */
 121         public function getWithSetCallback( $key, callable $callback ) {
 122                 if ( $this->has( $key ) ) {
 123                         $value = $this->get( $key );
 124                 } else {
 125                         $value = call_user_func( $callback );
 126                         if ( $value !== false ) {
 127                                 $this->set( $key, $value );
 128                         }
 129                 }
 130
 131                 return $value;
 132         }
 133
 134         /**
 135          * Clear one or several cache entries, or all cache entries
 136          *
 137          * @param string|array $keys
 138          * @return void
 139          */
 140         public function clear( $keys = null ) {
 141                 if ( $keys === null ) {
 142                         $this->cache = [];
 143                 } else {
 144                         foreach ( (array)$keys as $key ) {
 145                                 unset( $this->cache[$key] );
 146                         }
 147                 }
 148         }
 149
 150         /**
 151          * Push an entry to the top of the cache
 152          *
 153          * @param string $key
 154          */
 155         protected function ping( $key ) {
 156                 $item = $this->cache[$key];
 157                 unset( $this->cache[$key] );
 158                 $this->cache[$key] = $item;
 159         }
 160 }