PHPSessionHandler: Implement SessionHandlerInterface

[mediawiki.git] / includes / objectcache / ObjectCache.php

<?php
/**
 * Functions to get cache objects.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup Cache
 */

use MediaWiki\Logger\LoggerFactory;

/**
 * Functions to get cache objects
 *
 * The word "cache" has two main dictionary meanings, and both
 * are used in this factory class. They are:
 *
 *   - a) Cache (the computer science definition).
 *        A place to store copies or computations on existing data for
 *        higher access speeds.
 *   - b) Storage.
 *        A place to store lightweight data that is not canonically
 *        stored anywhere else (e.g. a "hoard" of objects).
 *
 * The former should always use strongly consistent stores, so callers don't
 * have to deal with stale reads. The later may be eventually consistent, but
 * callers can use BagOStuff:READ_LATEST to see the latest available data.
 *
 * Primary entry points:
 *
 * - ObjectCache::getMainWANInstance()
 *   Purpose: Memory cache.
 *   Stored in the local data-center's main cache (keyspace different from local-cluster cache).
 *   Delete events are broadcasted to other DCs main cache. See WANObjectCache for details.
 *
 * - ObjectCache::getLocalServerInstance( $fallbackType )
 *   Purpose: Memory cache for very hot keys.
 *   Stored only on the individual web server (typically APC for web requests,
 *   and EmptyBagOStuff in CLI mode).
 *   Not replicated to the other servers.
 *
 * - ObjectCache::getLocalClusterInstance()
 *   Purpose: Memory storage for per-cluster coordination and tracking.
 *   A typical use case would be a rate limit counter or cache regeneration mutex.
 *   Stored centrally within the local data-center. Not replicated to other DCs.
 *   Configured by $wgMainCacheType.
 *
 * - ObjectCache::getMainStashInstance()
 *   Purpose: Ephemeral global storage.
 *   Stored centrally within the primary data-center.
 *   Changes are applied there first and replicated to other DCs (best-effort).
 *   To retrieve the latest value (e.g. not from a slave), use BagOStuff::READ_LATEST.
 *   This store may be subject to LRU style evictions.
 *
 * - ObjectCache::getInstance( $cacheType )
 *   Purpose: Special cases (like tiered memory/disk caches).
 *   Get a specific cache type by key in $wgObjectCaches.
 *
 * All the above cache instances (BagOStuff and WANObjectCache) have their makeKey()
 * method scoped to the *current* wiki ID. Use makeGlobalKey() to avoid this scoping
 * when using keys that need to be shared amongst wikis.
 *
 * @ingroup Cache
 */
class ObjectCache {
        /** @var BagOStuff[] Map of (id => BagOStuff) */
        public static $instances = array();
        /** @var WANObjectCache[] Map of (id => WANObjectCache) */
        public static $wanInstances = array();

        /**
         * Get a cached instance of the specified type of cache object.
         *
         * @param string $id A key in $wgObjectCaches.
         * @return BagOStuff
         */
        public static function getInstance( $id ) {
                if ( !isset( self::$instances[$id] ) ) {
                        self::$instances[$id] = self::newFromId( $id );
                }

                return self::$instances[$id];
        }

        /**
         * Get a cached instance of the specified type of WAN cache object.
         *
         * @since 1.26
         * @param string $id A key in $wgWANObjectCaches.
         * @return WANObjectCache
         */
        public static function getWANInstance( $id ) {
                if ( !isset( self::$wanInstances[$id] ) ) {
                        self::$wanInstances[$id] = self::newWANCacheFromId( $id );
                }

                return self::$wanInstances[$id];
        }

        /**
         * Create a new cache object of the specified type.
         *
         * @param string $id A key in $wgObjectCaches.
         * @return BagOStuff
         * @throws MWException
         */
        public static function newFromId( $id ) {
                global $wgObjectCaches;

                if ( !isset( $wgObjectCaches[$id] ) ) {
                        throw new MWException( "Invalid object cache type \"$id\" requested. " .
                                "It is not present in \$wgObjectCaches." );
                }

                return self::newFromParams( $wgObjectCaches[$id] );
        }

        /**
         * Get the default keyspace for this wiki.
         *
         * This is either the value of the `CachePrefix` configuration variable,
         * or (if the former is unset) the `DBname` configuration variable, with
         * `DBprefix` (if defined).
         *
         * @return string
         */
        public static function getDefaultKeyspace() {
                global $wgCachePrefix;

                $keyspace = $wgCachePrefix;
                if ( is_string( $keyspace ) && $keyspace !== '' ) {
                        return $keyspace;
                }

                return wfWikiID();
        }

        /**
         * Create a new cache object from parameters.
         *
         * @param array $params Must have 'factory' or 'class' property.
         *  - factory: Callback passed $params that returns BagOStuff.
         *  - class: BagOStuff subclass constructed with $params.
         *  - loggroup: Alias to set 'logger' key with LoggerFactory group.
         *  - .. Other parameters passed to factory or class.
         * @return BagOStuff
         * @throws MWException
         */
        public static function newFromParams( $params ) {
                if ( isset( $params['loggroup'] ) ) {
                        $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
                } else {
                        $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
                }
                if ( !isset( $params['keyspace'] ) ) {
                        $params['keyspace'] = self::getDefaultKeyspace();
                }
                if ( isset( $params['factory'] ) ) {
                        return call_user_func( $params['factory'], $params );
                } elseif ( isset( $params['class'] ) ) {
                        $class = $params['class'];
                        // Automatically set the 'async' update handler
                        if ( $class === 'MultiWriteBagOStuff' ) {
                                $params['asyncHandler'] = isset( $params['asyncHandler'] )
                                        ? $params['asyncHandler']
                                        : 'DeferredUpdates::addCallableUpdate';
                        }
                        // Do b/c logic for MemcachedBagOStuff
                        if ( is_subclass_of( $class, 'MemcachedBagOStuff' ) ) {
                                if ( !isset( $params['servers'] ) ) {
                                        $params['servers'] = $GLOBALS['wgMemCachedServers'];
                                }
                                if ( !isset( $params['debug'] ) ) {
                                        $params['debug'] = $GLOBALS['wgMemCachedDebug'];
                                }
                                if ( !isset( $params['persistent'] ) ) {
                                        $params['persistent'] = $GLOBALS['wgMemCachedPersistent'];
                                }
                                if ( !isset( $params['timeout'] ) ) {
                                        $params['timeout'] = $GLOBALS['wgMemCachedTimeout'];
                                }
                        }
                        return new $class( $params );
                } else {
                        throw new MWException( "The definition of cache type \""
                                . print_r( $params, true ) . "\" lacks both "
                                . "factory and class parameters." );
                }
        }

        /**
         * Factory function for CACHE_ANYTHING (referenced from DefaultSettings.php)
         *
         * CACHE_ANYTHING means that stuff has to be cached, not caching is not an option.
         * If a caching method is configured for any of the main caches ($wgMainCacheType,
         * $wgMessageCacheType, $wgParserCacheType), then CACHE_ANYTHING will effectively
         * be an alias to the configured cache choice for that.
         * If no cache choice is configured (by default $wgMainCacheType is CACHE_NONE),
         * then CACHE_ANYTHING will forward to CACHE_DB.
         *
         * @param array $params
         * @return BagOStuff
         */
        public static function newAnything( $params ) {
                global $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType;
                $candidates = array( $wgMainCacheType, $wgMessageCacheType, $wgParserCacheType );
                foreach ( $candidates as $candidate ) {
                        if ( $candidate !== CACHE_NONE && $candidate !== CACHE_ANYTHING ) {
                                return self::getInstance( $candidate );
                        }
                }
                return self::getInstance( CACHE_DB );
        }

        /**
         * Factory function for CACHE_ACCEL (referenced from DefaultSettings.php)
         *
         * This will look for any APC style server-local cache.
         * A fallback cache can be specified if none is found.
         *
         *     // Direct calls
         *     ObjectCache::getLocalServerInstance( $fallbackType );
         *
         *     // From $wgObjectCaches via newFromParams()
         *     ObjectCache::getLocalServerInstance( array( 'fallback' => $fallbackType ) );
         *
         * @param int|string|array $fallback Fallback cache or parameter map with 'fallback'
         * @return BagOStuff
         * @throws MWException
         * @since 1.27
         */
        public static function getLocalServerInstance( $fallback = CACHE_NONE ) {
                if ( function_exists( 'apc_fetch' ) ) {
                        $id = 'apc';
                } elseif ( function_exists( 'xcache_get' ) && wfIniGetBool( 'xcache.var_size' ) ) {
                        $id = 'xcache';
                } elseif ( function_exists( 'wincache_ucache_get' ) ) {
                        $id = 'wincache';
                } else {
                        if ( is_array( $fallback ) ) {
                                $id = isset( $fallback['fallback'] ) ? $fallback['fallback'] : CACHE_NONE;
                        } else {
                                $id = $fallback;
                        }
                }

                return self::getInstance( $id );
        }

        /**
         * @param array $params [optional] Array key 'fallback' for $fallback.
         * @param int|string $fallback Fallback cache, e.g. (CACHE_NONE, "hash") (since 1.24)
         * @return BagOStuff
         * @deprecated 1.27
         */
        public static function newAccelerator( $params = array(), $fallback = null ) {
                if ( $fallback === null ) {
                        // The is_array check here is needed because in PHP 5.3:
                        // $a = 'hash'; isset( $params['fallback'] ); yields true
                        if ( is_array( $params ) && isset( $params['fallback'] ) ) {
                                $fallback = $params['fallback'];
                        } elseif ( !is_array( $params ) ) {
                                $fallback = $params;
                        }
                }

                return self::getLocalServerInstance( $fallback );
        }

        /**
         * Create a new cache object of the specified type.
         *
         * @since 1.26
         * @param string $id A key in $wgWANObjectCaches.
         * @return WANObjectCache
         * @throws MWException
         */
        public static function newWANCacheFromId( $id ) {
                global $wgWANObjectCaches;

                if ( !isset( $wgWANObjectCaches[$id] ) ) {
                        throw new MWException( "Invalid object cache type \"$id\" requested. " .
                                "It is not present in \$wgWANObjectCaches." );
                }

                $params = $wgWANObjectCaches[$id];
                $class = $params['relayerConfig']['class'];
                $params['relayer'] = new $class( $params['relayerConfig'] );
                $params['cache'] = self::newFromId( $params['cacheId'] );
                if ( isset( $params['loggroup'] ) ) {
                        $params['logger'] = LoggerFactory::getInstance( $params['loggroup'] );
                } else {
                        $params['logger'] = LoggerFactory::getInstance( 'objectcache' );
                }
                $class = $params['class'];

                return new $class( $params );
        }

        /**
         * Get the main cluster-local cache object.
         *
         * @since 1.27
         * @return BagOStuff
         */
        public static function getLocalClusterInstance() {
                global $wgMainCacheType;

                return self::getInstance( $wgMainCacheType );
        }

        /**
         * Get the main WAN cache object.
         *
         * @since 1.26
         * @return WANObjectCache
         */
        public static function getMainWANInstance() {
                global $wgMainWANCache;

                return self::getWANInstance( $wgMainWANCache );
        }

        /**
         * Get the cache object for the main stash.
         *
         * Stash objects are BagOStuff instances suitable for storing light
         * weight data that is not canonically stored elsewhere (such as RDBMS).
         * Stashes should be configured to propagate changes to all data-centers.
         *
         * Callers should be prepared for:
         *   - a) Writes to be slower in non-"primary" (e.g. HTTP GET/HEAD only) DCs
         *   - b) Reads to be eventually consistent, e.g. for get()/getMulti()
         * In general, this means avoiding updates on idempotent HTTP requests and
         * avoiding an assumption of perfect serializability (or accepting anomalies).
         * Reads may be eventually consistent or data might rollback as nodes flap.
         * Callers can use BagOStuff:READ_LATEST to see the latest available data.
         *
         * @return BagOStuff
         * @since 1.26
         */
        public static function getMainStashInstance() {
                global $wgMainStash;

                return self::getInstance( $wgMainStash );
        }

        /**
         * Clear all the cached instances.
         */
        public static function clear() {
                self::$instances = array();
                self::$wanInstances = array();
        }
}