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          * @param array $values Key/value map in order of increasingly recent access
  53          * @param int $maxKeys
  54          * @return MapCacheLRU
  55          * @since 1.30
  56          */
  57         public static function newFromArray( array $values, $maxKeys ) {
  58                 $mapCache = new self( $maxKeys );
  59                 $mapCache->cache = ( count( $values ) > $maxKeys )
  60                         ? array_slice( $values, -$maxKeys, null, true )
  61                         : $values;
  62
  63                 return $mapCache;
  64         }
  65
  66         /**
  67          * @return array Key/value map in order of increasingly recent access
  68          * @since 1.30
  69          */
  70         public function toArray() {
  71                 return $this->cache;
  72         }
  73
  74         /**
  75          * Set a key/value pair.
  76          * This will prune the cache if it gets too large based on LRU.
  77          * If the item is already set, it will be pushed to the top of the cache.
  78          *
  79          * To reduce evictions due to one-off use of many new keys, $rank can be
  80          * set to have keys start at the top of a bottom fraction of the list. A value
  81          * of 3/8 means values start at the top of the bottom 3/8s of the list and are
  82          * moved to the top of the list when accessed a second time.
  83          *
  84          * @param string $key
  85          * @param mixed $value
  86          * @param float $rank Bottom fraction of the list where keys start off [Default: 1.0]
  87          * @return void
  88          */
  89         public function set( $key, $value, $rank = 1.0 ) {
  90                 if ( $this->has( $key ) ) {
  91                         $this->ping( $key );
  92                 } elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
  93                         reset( $this->cache );
  94                         $evictKey = key( $this->cache );
  95                         unset( $this->cache[$evictKey] );
  96                 }
  97
  98                 if ( $rank < 1.0 && $rank > 0 ) {
  99                         $offset = intval( $rank * count( $this->cache ) );
 100                         $this->cache = array_slice( $this->cache, 0, $offset, true )
 101                                 + [ $key => $value ]
 102                                 + array_slice( $this->cache, $offset, null, true );
 103                 } else {
 104                         $this->cache[$key] = $value;
 105                 }
 106         }
 107
 108         /**
 109          * Check if a key exists
 110          *
 111          * @param string $key
 112          * @return bool
 113          */
 114         public function has( $key ) {
 115                 if ( !is_int( $key ) && !is_string( $key ) ) {
 116                         throw new UnexpectedValueException(
 117                                 __METHOD__ . ' called with invalid key. Must be string or integer.' );
 118                 }
 119                 return array_key_exists( $key, $this->cache );
 120         }
 121
 122         /**
 123          * Get the value for a key.
 124          * This returns null if the key is not set.
 125          * If the item is already set, it will be pushed to the top of the cache.
 126          *
 127          * @param string $key
 128          * @return mixed Returns null if the key was not found
 129          */
 130         public function get( $key ) {
 131                 if ( !$this->has( $key ) ) {
 132                         return null;
 133                 }
 134
 135                 $this->ping( $key );
 136
 137                 return $this->cache[$key];
 138         }
 139
 140         /**
 141          * @return array
 142          * @since 1.25
 143          */
 144         public function getAllKeys() {
 145                 return array_keys( $this->cache );
 146         }
 147
 148         /**
 149          * Get an item with the given key, producing and setting it if not found.
 150          *
 151          * If the callback returns false, then nothing is stored.
 152          *
 153          * @since 1.28
 154          * @param string $key
 155          * @param callable $callback Callback that will produce the value
 156          * @param float $rank Bottom fraction of the list where keys start off [Default: 1.0]
 157          * @return mixed The cached value if found or the result of $callback otherwise
 158          */
 159         public function getWithSetCallback( $key, callable $callback, $rank = 1.0 ) {
 160                 if ( $this->has( $key ) ) {
 161                         $value = $this->get( $key );
 162                 } else {
 163                         $value = call_user_func( $callback );
 164                         if ( $value !== false ) {
 165                                 $this->set( $key, $value, $rank );
 166                         }
 167                 }
 168
 169                 return $value;
 170         }
 171
 172         /**
 173          * Clear one or several cache entries, or all cache entries
 174          *
 175          * @param string|array $keys
 176          * @return void
 177          */
 178         public function clear( $keys = null ) {
 179                 if ( $keys === null ) {
 180                         $this->cache = [];
 181                 } else {
 182                         foreach ( (array)$keys as $key ) {
 183                                 unset( $this->cache[$key] );
 184                         }
 185                 }
 186         }
 187
 188         /**
 189          * Push an entry to the top of the cache
 190          *
 191          * @param string $key
 192          */
 193         protected function ping( $key ) {
 194                 $item = $this->cache[$key];
 195                 unset( $this->cache[$key] );
 196                 $this->cache[$key] = $item;
 197         }
 198 }