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 use Wikimedia\Assert\Assert;
  24
  25 /**
  26  * Handles per process caching of items
  27  * @ingroup Cache
  28  */
  29 class ProcessCacheLRU {
  30         /** @var Array */
  31         protected $cache = array(); // (key => prop => value)
  32
  33         /** @var Array */
  34         protected $cacheTimes = array(); // (key => prop => UNIX timestamp)
  35
  36         protected $maxCacheKeys; // integer; max entries
  37
  38         /**
  39          * @param int $maxKeys Maximum number of entries allowed (min 1).
  40          * @throws UnexpectedValueException When $maxCacheKeys is not an int or =< 0.
  41          */
  42         public function __construct( $maxKeys ) {
  43                 $this->resize( $maxKeys );
  44         }
  45
  46         /**
  47          * Set a property field for a cache entry.
  48          * This will prune the cache if it gets too large based on LRU.
  49          * If the item is already set, it will be pushed to the top of the cache.
  50          *
  51          * @param string $key
  52          * @param string $prop
  53          * @param mixed $value
  54          * @return void
  55          */
  56         public function set( $key, $prop, $value ) {
  57                 if ( isset( $this->cache[$key] ) ) {
  58                         $this->ping( $key ); // push to top
  59                 } elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
  60                         reset( $this->cache );
  61                         $evictKey = key( $this->cache );
  62                         unset( $this->cache[$evictKey] );
  63                         unset( $this->cacheTimes[$evictKey] );
  64                 }
  65                 $this->cache[$key][$prop] = $value;
  66                 $this->cacheTimes[$key][$prop] = microtime( true );
  67         }
  68
  69         /**
  70          * Check if a property field exists for a cache entry.
  71          *
  72          * @param string $key
  73          * @param string $prop
  74          * @param float $maxAge Ignore items older than this many seconds (since 1.21)
  75          * @return bool
  76          */
  77         public function has( $key, $prop, $maxAge = 0.0 ) {
  78                 if ( isset( $this->cache[$key][$prop] ) ) {
  79                         return ( $maxAge <= 0 ||
  80                                 ( microtime( true ) - $this->cacheTimes[$key][$prop] ) <= $maxAge
  81                         );
  82                 }
  83
  84                 return false;
  85         }
  86
  87         /**
  88          * Get a property field for a cache entry.
  89          * This returns null if the property is not set.
  90          * If the item is already set, it will be pushed to the top of the cache.
  91          *
  92          * @param string $key
  93          * @param string $prop
  94          * @return mixed
  95          */
  96         public function get( $key, $prop ) {
  97                 if ( isset( $this->cache[$key][$prop] ) ) {
  98                         // push to top
  99                         $this->ping( $key );
 100                         return $this->cache[$key][$prop];
 101                 } else {
 102                         return null;
 103                 }
 104         }
 105
 106         /**
 107          * Clear one or several cache entries, or all cache entries.
 108          *
 109          * @param string|array $keys
 110          * @return void
 111          */
 112         public function clear( $keys = null ) {
 113                 if ( $keys === null ) {
 114                         $this->cache = array();
 115                         $this->cacheTimes = array();
 116                 } else {
 117                         foreach ( (array)$keys as $key ) {
 118                                 unset( $this->cache[$key] );
 119                                 unset( $this->cacheTimes[$key] );
 120                         }
 121                 }
 122         }
 123
 124         /**
 125          * Resize the maximum number of cache entries, removing older entries as needed
 126          *
 127          * @param int $maxKeys
 128          * @return void
 129          * @throws UnexpectedValueException
 130          */
 131         public function resize( $maxKeys ) {
 132                 Assert::parameterType( 'integer', $maxKeys, '$maxKeys' );
 133                 Assert::parameter( $maxKeys >= 1, '$maxKeys', 'must be >= 1' );
 134
 135                 $this->maxCacheKeys = $maxKeys;
 136                 while ( count( $this->cache ) > $this->maxCacheKeys ) {
 137                         reset( $this->cache );
 138                         $evictKey = key( $this->cache );
 139                         unset( $this->cache[$evictKey] );
 140                         unset( $this->cacheTimes[$evictKey] );
 141                 }
 142         }
 143
 144         /**
 145          * Push an entry to the top of the cache
 146          *
 147          * @param string $key
 148          */
 149         protected function ping( $key ) {
 150                 $item = $this->cache[$key];
 151                 unset( $this->cache[$key] );
 152                 $this->cache[$key] = $item;
 153         }
 154 }