includes/objectcache/ObjectCache.php

   1 <?php
   2 /**
   3  * Functions to get cache objects.
   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 use MediaWiki\Logger\LoggerFactory;
  25
  26 /**
  27  * Functions to get cache objects
  28  *
  29  * The word "cache" has two main dictionary meanings, and both
  30  * are used in this factory class. They are:
  31  *
  32  *   - a) Cache (the computer science definition).
  33  *        A place to store copies or computations on existing data for
  34  *        higher access speeds.
  35  *   - b) Storage.
  36  *        A place to store lightweight data that is not canonically
  37  *        stored anywhere else (e.g. a "hoard" of objects).
  38  *
  39  * The former should always use strongly consistent stores, so callers don't
  40  * have to deal with stale reads. The later may be eventually consistent, but
  41  * callers can use BagOStuff:READ_LATEST to see the latest available data.
  42  *
  43  * Primary entry points:
  44  *
  45  * - ObjectCache::newAccelerator( $fallbackType )
  46  *   Purpose: Cache.
  47  *   Stored only on the individual web server.
  48  *   Not associated with other servers.
  49  *
  50  * - wfGetMainCache()
  51  *   Purpose: Cache.
  52  *   Stored centrally within the local data-center.
  53  *   Not replicated to other DCs.
  54  *   Also known as $wgMemc. Configured by $wgMainCacheType.
  55  *
  56  * - ObjectCache::getMainWANInstance()
  57  *   Purpose: Cache.
  58  *   Stored in the local data-center's main cache (uses different cache keys).
  59  *   Delete events are broadcasted to other DCs. See WANObjectCache for details.
  60  *
  61  * - ObjectCache::getMainStashInstance()
  62  *   Purpose: Ephemeral storage.
  63  *   Stored centrally within the local data-center.
  64  *   Changes are replicated to other DCs (eventually consistent).
  65  *   To retrieve the latest value (e.g. not from a slave), use BagOStuff:READ_LATEST.
  66  *   This store may be subject to LRU style evictions.
  67  *
  68  * - wfGetCache( $cacheType )
  69  *   Get a specific cache type by key in $wgObjectCaches.
  70  *
  71  * @ingroup Cache
  72  */
  73 class ObjectCache {
  74         /** @var Array Map of (id => BagOStuff) */
  75         public static $instances = array();
  76
  77         /** @var Array Map of (id => WANObjectCache) */
  78         public static $wanInstances = array();
  79
  80         /**
  81          * Get a cached instance of the specified type of cache object.
  82          *
  83          * @param string $id A key in $wgObjectCaches.
  84          * @return BagOStuff
  85          */
  86         public static function getInstance( $id ) {
  87                 if ( !isset( self::$instances[$id] ) ) {
  88                         self::$instances[$id] = self::newFromId( $id );
  89                 }
  90
  91                 return self::$instances[$id];
  92         }
  93
  94         /**
  95          * Get a cached instance of the specified type of WAN cache object.
  96          *
  97          * @since 1.26
  98          * @param string $id A key in $wgWANObjectCaches.
  99          * @return WANObjectCache
 100          */
 101         public static function getWANInstance( $id ) {
 102                 if ( !isset( self::$wanInstances[$id] ) ) {
 103                         self::$wanInstances[$id] = self::newWANCacheFromId( $id );
 104                 }
 105
 106                 return self::$wanInstances[$id];
 107         }
 108
 109         /**
 110          * Create a new cache object of the specified type.
 111          *
 112          * @param string $id A key in $wgObjectCaches.
 113          * @return BagOStuff
 114          * @throws MWException
 115          */
 116         public static function newFromId( $id ) {
 117                 global $wgObjectCaches;
 118
 119                 if ( !isset( $wgObjectCaches[$id] ) ) {
 120                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 121                                 "It is not present in \$wgObjectCaches." );
 122                 }
 123
 124                 return self::newFromParams( $wgObjectCaches[$id] );
 125         }
 126
 127         /**
 128          * Create a new cache object from parameters.
 129          *
 130          * @param array $params Must have 'factory' or 'class' property.
 131          *  - factory: Callback passed $params that returns BagOStuff.
 132          *  - class: BagOStuff subclass constructed with $params.
 133          *  - loggroup: Alias to set 'logger' key with LoggerFactory group.
 134          *  - .. Other parameters passed to factory or class.
 135          * @return BagOStuff
 136          * @throws MWException
 137          */
 138         public static function newFromParams( $params ) {
 139                 if ( isset( $params['loggroup'] ) ) {
 140                         $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
 141                 } else {
 142                         // For backwards-compatability with custom parameters, lets not
 143                         // have all logging suddenly disappear
 144                         $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
 145                 }
 146                 if ( isset( $params['factory'] ) ) {
 147                         return call_user_func( $params['factory'], $params );
 148                 } elseif ( isset( $params['class'] ) ) {
 149                         $class = $params['class'];
 150                         return new $class( $params );
 151                 } else {
 152                         throw new MWException( "The definition of cache type \""
 153                                 . print_r( $params, true ) . "\" lacks both "
 154                                 . "factory and class parameters." );
 155                 }
 156         }
 157
 158         /**
 159          * Factory function for CACHE_ANYTHING (referenced from DefaultSettings.php)
 160          *
 161          * CACHE_ANYTHING means that stuff has to be cached, not caching is not an option.
 162          * If a caching method is configured for any of the main caches ($wgMainCacheType,
 163          * $wgMessageCacheType, $wgParserCacheType), then CACHE_ANYTHING will effectively
 164          * be an alias to the configured cache choice for that.
 165          * If no cache choice is configured (by default $wgMainCacheType is CACHE_NONE),
 166          * then CACHE_ANYTHING will forward to CACHE_DB.
 167          *
 168          * @param array $params
 169          * @return BagOStuff
 170          */
 171         public static function newAnything( $params ) {
 172                 global $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType;
 173                 $candidates = array( $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType );
 174                 foreach ( $candidates as $candidate ) {
 175                         if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
 176                                 return self::getInstance( $candidate );
 177                         }
 178                 }
 179                 return self::getInstance( CACHE_DB );
 180         }
 181
 182         /**
 183          * Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
 184          *
 185          * This will look for any APC style server-local cache.
 186          * A fallback cache can be specified if none is found.
 187          *
 188          * @param array $params [optional]
 189          * @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
 190          * @return BagOStuff
 191          * @throws MWException
 192          */
 193         public static function newAccelerator( $params = array(), $fallback = null ) {
 194                 if ( !is_array( $params ) && $fallback === null ) {
 195                         $fallback = $params;
 196                 }
 197                 if ( function_exists( 'apc_fetch' ) ) {
 198                         $id = 'apc';
 199                 } elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
 200                         $id = 'xcache';
 201                 } elseif ( function_exists( 'wincache_ucache_get' ) ) {
 202                         $id = 'wincache';
 203                 } else {
 204                         if ( $fallback === null ) {
 205                                 throw new MWException( 'CACHE_ACCEL requested but no suitable object ' .
 206                                         'cache is present. You may want to install APC.' );
 207                         }
 208                         $id = $fallback;
 209                 }
 210                 return self::newFromId( $id );
 211         }
 212
 213         /**
 214          * Factory function that creates a memcached client object.
 215          *
 216          * This always uses the PHP client, since the PECL client has a different
 217          * hashing scheme and a different interpretation of the flags bitfield, so
 218          * switching between the two clients randomly would be disastrous.
 219          *
 220          * @param array $params
 221          * @return MemcachedPhpBagOStuff
 222          */
 223         public static function newMemcached( $params ) {
 224                 return new MemcachedPhpBagOStuff( $params );
 225         }
 226
 227         /**
 228          * Create a new cache object of the specified type.
 229          *
 230          * @since 1.26
 231          * @param string $id A key in $wgWANObjectCaches.
 232          * @return WANObjectCache
 233          * @throws MWException
 234          */
 235         public static function newWANCacheFromId( $id ) {
 236                 global $wgWANObjectCaches;
 237
 238                 if ( !isset( $wgWANObjectCaches[$id] ) ) {
 239                         throw new MWException( "Invalid object cache type \"$id\" requested. " .
 240                                 "It is not present in \$wgWANObjectCaches." );
 241                 }
 242
 243                 $params = $wgWANObjectCaches[$id];
 244                 $class = $params['relayerConfig']['class'];
 245                 $params['relayer'] = new $class( $params['relayerConfig'] );
 246                 $params['cache'] = self::newFromId( $params['cacheId'] );
 247                 $class = $params['class'];
 248
 249                 return new $class( $params );
 250         }
 251
 252         /**
 253          * Get the main WAN cache object.
 254          *
 255          * @since 1.26
 256          * @return WANObjectCache
 257          */
 258         public static function getMainWANInstance() {
 259                 global $wgMainWANCache;
 260
 261                 return self::getWANInstance( $wgMainWANCache );
 262         }
 263
 264         /**
 265          * Get the cache object for the main stash.
 266          *
 267          * Stash objects are BagOStuff instances suitable for storing light
 268          * weight data that is not canonically stored elsewhere (such as RDBMS).
 269          * Stashes should be configured to propagate changes to all data-centers.
 270          *
 271          * Callers should be prepared for:
 272          *   - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
 273          *   - b) Reads to be eventually consistent, e.g. for get()/getMulti()
 274          * In general, this means avoiding updates on idempotent HTTP requests and
 275          * avoiding an assumption of perfect serializability (or accepting anomalies).
 276          * Reads may be eventually consistent or data might rollback as nodes flap.
 277          * Callers can use BagOStuff:READ_LATEST to see the latest available data.
 278          *
 279          * @return BagOStuff
 280          * @since 1.26
 281          */
 282         public static function getMainStashInstance() {
 283                 global $wgMainStash;
 284
 285                 return self::getInstance( $wgMainStash );
 286         }
 287
 288         /**
 289          * Clear all the cached instances.
 290          */
 291         public static function clear() {
 292                 self::$instances = array();
 293                 self::$wanInstances = array();
 294         }
 295 }