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  * Class for process caching individual properties of expiring items
  27  *
  28  * When the key for an entire item is deleted, all properties for it are deleted
  29  *
  30  * @ingroup Cache
  31  */
  32 class ProcessCacheLRU {
  33         /** @var array */
  34         protected $cache = []; // (key => prop => value)
  35
  36         /** @var array */
  37         protected $cacheTimes = []; // (key => prop => UNIX timestamp)
  38
  39         protected $maxCacheKeys; // integer; max entries
  40
  41         /**
  42          * @param int $maxKeys Maximum number of entries allowed (min 1).
  43          * @throws UnexpectedValueException When $maxCacheKeys is not an int or =< 0.
  44          */
  45         public function __construct( $maxKeys ) {
  46                 $this->resize( $maxKeys );
  47         }
  48
  49         /**
  50          * Set a property field for a cache entry.
  51          * This will prune the cache if it gets too large based on LRU.
  52          * If the item is already set, it will be pushed to the top of the cache.
  53          *
  54          * @param string $key
  55          * @param string $prop
  56          * @param mixed $value
  57          * @return void
  58          */
  59         public function set( $key, $prop, $value ) {
  60                 if ( isset( $this->cache[$key] ) ) {
  61                         $this->ping( $key );
  62                 } elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
  63                         reset( $this->cache );
  64                         $evictKey = key( $this->cache );
  65                         unset( $this->cache[$evictKey] );
  66                         unset( $this->cacheTimes[$evictKey] );
  67                 }
  68                 $this->cache[$key][$prop] = $value;
  69                 $this->cacheTimes[$key][$prop] = microtime( true );
  70         }
  71
  72         /**
  73          * Check if a property field exists for a cache entry.
  74          *
  75          * @param string $key
  76          * @param string $prop
  77          * @param float $maxAge Ignore items older than this many seconds (since 1.21)
  78          * @return bool
  79          */
  80         public function has( $key, $prop, $maxAge = 0.0 ) {
  81                 if ( isset( $this->cache[$key][$prop] ) ) {
  82                         return ( $maxAge <= 0 ||
  83                                 ( microtime( true ) - $this->cacheTimes[$key][$prop] ) <= $maxAge
  84                         );
  85                 }
  86
  87                 return false;
  88         }
  89
  90         /**
  91          * Get a property field for a cache entry.
  92          * This returns null if the property is not set.
  93          * If the item is already set, it will be pushed to the top of the cache.
  94          *
  95          * @param string $key
  96          * @param string $prop
  97          * @return mixed
  98          */
  99         public function get( $key, $prop ) {
 100                 if ( !isset( $this->cache[$key][$prop] ) ) {
 101                         return null;
 102                 }
 103                 $this->ping( $key );
 104                 return $this->cache[$key][$prop];
 105         }
 106
 107         /**
 108          * Clear one or several cache entries, or all cache entries.
 109          *
 110          * @param string|array $keys
 111          * @return void
 112          */
 113         public function clear( $keys = null ) {
 114                 if ( $keys === null ) {
 115                         $this->cache = [];
 116                         $this->cacheTimes = [];
 117                 } else {
 118                         foreach ( (array)$keys as $key ) {
 119                                 unset( $this->cache[$key] );
 120                                 unset( $this->cacheTimes[$key] );
 121                         }
 122                 }
 123         }
 124
 125         /**
 126          * Resize the maximum number of cache entries, removing older entries as needed
 127          *
 128          * @param int $maxKeys
 129          * @return void
 130          * @throws UnexpectedValueException
 131          */
 132         public function resize( $maxKeys ) {
 133                 Assert::parameterType( 'integer', $maxKeys, '$maxKeys' );
 134                 Assert::parameter( $maxKeys > 0, '$maxKeys', 'must be above zero' );
 135
 136                 $this->maxCacheKeys = $maxKeys;
 137                 while ( count( $this->cache ) > $this->maxCacheKeys ) {
 138                         reset( $this->cache );
 139                         $evictKey = key( $this->cache );
 140                         unset( $this->cache[$evictKey] );
 141                         unset( $this->cacheTimes[$evictKey] );
 142                 }
 143         }
 144
 145         /**
 146          * Push an entry to the top of the cache
 147          *
 148          * @param string $key
 149          */
 150         protected function ping( $key ) {
 151                 $item = $this->cache[$key];
 152                 unset( $this->cache[$key] );
 153                 $this->cache[$key] = $item;
 154         }
 155
 156         /**
 157          * Get cache size
 158          * @return int
 159          */
 160         public function getSize() {
 161                 return $this->maxCacheKeys;
 162         }
 163 }