includes/libs/ProcessCacheLRU.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 per process caching of items
  26  * @ingroup Cache
  27  */
  28 class ProcessCacheLRU {
  29         /** @var Array */
  30         protected $cache = array(); // (key => prop => value)
  31
  32         /** @var Array */
  33         protected $cacheTimes = array(); // (key => prop => UNIX timestamp)
  34
  35         protected $maxCacheKeys; // integer; max entries
  36
  37         /**
  38          * @param int $maxKeys Maximum number of entries allowed (min 1).
  39          * @throws UnexpectedValueException When $maxCacheKeys is not an int or =< 0.
  40          */
  41         public function __construct( $maxKeys ) {
  42                 $this->resize( $maxKeys );
  43         }
  44
  45         /**
  46          * Set a property field for a cache entry.
  47          * This will prune the cache if it gets too large based on LRU.
  48          * If the item is already set, it will be pushed to the top of the cache.
  49          *
  50          * @param string $key
  51          * @param string $prop
  52          * @param mixed $value
  53          * @return void
  54          */
  55         public function set( $key, $prop, $value ) {
  56                 if ( isset( $this->cache[$key] ) ) {
  57                         $this->ping( $key ); // push to top
  58                 } elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
  59                         reset( $this->cache );
  60                         $evictKey = key( $this->cache );
  61                         unset( $this->cache[$evictKey] );
  62                         unset( $this->cacheTimes[$evictKey] );
  63                 }
  64                 $this->cache[$key][$prop] = $value;
  65                 $this->cacheTimes[$key][$prop] = microtime( true );
  66         }
  67
  68         /**
  69          * Check if a property field exists for a cache entry.
  70          *
  71          * @param string $key
  72          * @param string $prop
  73          * @param float $maxAge Ignore items older than this many seconds (since 1.21)
  74          * @return bool
  75          */
  76         public function has( $key, $prop, $maxAge = 0.0 ) {
  77                 if ( isset( $this->cache[$key][$prop] ) ) {
  78                         return ( $maxAge <= 0 ||
  79                                 ( microtime( true ) - $this->cacheTimes[$key][$prop] ) <= $maxAge
  80                         );
  81                 }
  82
  83                 return false;
  84         }
  85
  86         /**
  87          * Get a property field for a cache entry.
  88          * This returns null if the property is not set.
  89          * If the item is already set, it will be pushed to the top of the cache.
  90          *
  91          * @param string $key
  92          * @param string $prop
  93          * @return mixed
  94          */
  95         public function get( $key, $prop ) {
  96                 if ( isset( $this->cache[$key][$prop] ) ) {
  97                         // push to top
  98                         $this->ping( $key );
  99                         return $this->cache[$key][$prop];
 100                 } else {
 101                         return null;
 102                 }
 103         }
 104
 105         /**
 106          * Clear one or several cache entries, or all cache entries.
 107          *
 108          * @param string|array $keys
 109          * @return void
 110          */
 111         public function clear( $keys = null ) {
 112                 if ( $keys === null ) {
 113                         $this->cache = array();
 114                         $this->cacheTimes = array();
 115                 } else {
 116                         foreach ( (array)$keys as $key ) {
 117                                 unset( $this->cache[$key] );
 118                                 unset( $this->cacheTimes[$key] );
 119                         }
 120                 }
 121         }
 122
 123         /**
 124          * Resize the maximum number of cache entries, removing older entries as needed
 125          *
 126          * @param int $maxKeys
 127          * @return void
 128          * @throws UnexpectedValueException
 129          */
 130         public function resize( $maxKeys ) {
 131                 if ( !is_int( $maxKeys ) || $maxKeys < 1 ) {
 132                         throw new UnexpectedValueException( __METHOD__ . " must be given an integer >= 1" );
 133                 }
 134                 $this->maxCacheKeys = $maxKeys;
 135                 while ( count( $this->cache ) > $this->maxCacheKeys ) {
 136                         reset( $this->cache );
 137                         $evictKey = key( $this->cache );
 138                         unset( $this->cache[$evictKey] );
 139                         unset( $this->cacheTimes[$evictKey] );
 140                 }
 141         }
 142
 143         /**
 144          * Push an entry to the top of the cache
 145          *
 146          * @param string $key
 147          */
 148         protected function ping( $key ) {
 149                 $item = $this->cache[$key];
 150                 unset( $this->cache[$key] );
 151                 $this->cache[$key] = $item;
 152         }
 153 }