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[mediawiki.git] / includes / libs / objectcache / MultiWriteBagOStuff.php

<?php
/**
 * Wrapper for object caching in different caches.
 *
 * 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
 */

/**
 * A cache class that replicates all writes to multiple child caches. Reads
 * are implemented by reading from the caches in the order they are given in
 * the configuration until a cache gives a positive result.
 *
 * @ingroup Cache
 */
class MultiWriteBagOStuff extends BagOStuff {
        /** @var BagOStuff[] */
        protected $caches;
        /** @var bool Use async secondary writes */
        protected $asyncWrites = false;

        /** Idiom for "write to all backends" */
        const ALL = INF;

        const UPGRADE_TTL = 3600; // TTL when a key is copied to a higher cache tier

        /**
         * $params include:
         *   - caches: A numbered array of either ObjectFactory::getObjectFromSpec
         *      arrays yeilding BagOStuff objects or direct BagOStuff objects.
         *      If using the former, the 'args' field *must* be set.
         *      The first cache is the primary one, being the first to
         *      be read in the fallback chain. Writes happen to all stores
         *      in the order they are defined. However, lock()/unlock() calls
         *      only use the primary store.
         *   - replication: Either 'sync' or 'async'. This controls whether writes
         *      to secondary stores are deferred when possible. Async writes
         *      require setting 'asyncHandler'. HHVM register_postsend_function() function.
         *      Async writes can increase the chance of some race conditions
         *      or cause keys to expire seconds later than expected. It is
         *      safe to use for modules when cached values: are immutable,
         *      invalidation uses logical TTLs, invalidation uses etag/timestamp
         *      validation against the DB, or merge() is used to handle races.
         * @param array $params
         * @throws InvalidArgumentException
         */
        public function __construct( $params ) {
                parent::__construct( $params );

                if ( empty( $params['caches'] ) || !is_array( $params['caches'] ) ) {
                        throw new InvalidArgumentException(
                                __METHOD__ . ': "caches" parameter must be an array of caches'
                        );
                }

                $this->caches = [];
                foreach ( $params['caches'] as $cacheInfo ) {
                        if ( $cacheInfo instanceof BagOStuff ) {
                                $this->caches[] = $cacheInfo;
                        } else {
                                if ( !isset( $cacheInfo['args'] ) ) {
                                        // B/C for when $cacheInfo was for ObjectCache::newFromParams().
                                        // Callers intenting this to be for ObjectFactory::getObjectFromSpec
                                        // should have set "args" per the docs above. Doings so avoids extra
                                        // (likely harmless) params (factory/class/calls) ending up in "args".
                                        $cacheInfo['args'] = [ $cacheInfo ];
                                }
                                $this->caches[] = ObjectFactory::getObjectFromSpec( $cacheInfo );
                        }
                }
                $this->mergeFlagMaps( $this->caches );

                $this->asyncWrites = (
                        isset( $params['replication'] ) &&
                        $params['replication'] === 'async' &&
                        is_callable( $this->asyncHandler )
                );
        }

        public function setDebug( $debug ) {
                foreach ( $this->caches as $cache ) {
                        $cache->setDebug( $debug );
                }
        }

        protected function doGet( $key, $flags = 0 ) {
                if ( ( $flags & self::READ_LATEST ) == self::READ_LATEST ) {
                        // If the latest write was a delete(), we do NOT want to fallback
                        // to the other tiers and possibly see the old value. Also, this
                        // is used by mergeViaLock(), which only needs to hit the primary.
                        return $this->caches[0]->get( $key, $flags );
                }

                $misses = 0; // number backends checked
                $value = false;
                foreach ( $this->caches as $cache ) {
                        $value = $cache->get( $key, $flags );
                        if ( $value !== false ) {
                                break;
                        }
                        ++$misses;
                }

                if ( $value !== false
                        && $misses > 0
                        && ( $flags & self::READ_VERIFIED ) == self::READ_VERIFIED
                ) {
                        $this->doWrite( $misses, $this->asyncWrites, 'set', $key, $value, self::UPGRADE_TTL );
                }

                return $value;
        }

        public function set( $key, $value, $exptime = 0, $flags = 0 ) {
                $asyncWrites = ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC )
                        ? false
                        : $this->asyncWrites;

                return $this->doWrite( self::ALL, $asyncWrites, 'set', $key, $value, $exptime );
        }

        public function delete( $key ) {
                return $this->doWrite( self::ALL, $this->asyncWrites, 'delete', $key );
        }

        public function add( $key, $value, $exptime = 0 ) {
                return $this->doWrite( self::ALL, $this->asyncWrites, 'add', $key, $value, $exptime );
        }

        public function incr( $key, $value = 1 ) {
                return $this->doWrite( self::ALL, $this->asyncWrites, 'incr', $key, $value );
        }

        public function decr( $key, $value = 1 ) {
                return $this->doWrite( self::ALL, $this->asyncWrites, 'decr', $key, $value );
        }

        public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
                // Only need to lock the first cache; also avoids deadlocks
                return $this->caches[0]->lock( $key, $timeout, $expiry, $rclass );
        }

        public function unlock( $key ) {
                // Only the first cache is locked
                return $this->caches[0]->unlock( $key );
        }

        public function getLastError() {
                return $this->caches[0]->getLastError();
        }

        public function clearLastError() {
                $this->caches[0]->clearLastError();
        }

        /**
         * Apply a write method to the first $count backing caches
         *
         * @param integer $count
         * @param bool $asyncWrites
         * @param string $method
         * @param mixed ...
         * @return bool
         */
        protected function doWrite( $count, $asyncWrites, $method /*, ... */ ) {
                $ret = true;
                $args = array_slice( func_get_args(), 3 );

                foreach ( $this->caches as $i => $cache ) {
                        if ( $i >= $count ) {
                                break; // ignore the lower tiers
                        }

                        if ( $i == 0 || !$asyncWrites ) {
                                // First store or in sync mode: write now and get result
                                if ( !call_user_func_array( [ $cache, $method ], $args ) ) {
                                        $ret = false;
                                }
                        } else {
                                // Secondary write in async mode: do not block this HTTP request
                                $logger = $this->logger;
                                call_user_func(
                                        $this->asyncHandler,
                                        function () use ( $cache, $method, $args, $logger ) {
                                                if ( !call_user_func_array( [ $cache, $method ], $args ) ) {
                                                        $logger->warning( "Async $method op failed" );
                                                }
                                        }
                                );
                        }
                }

                return $ret;
        }

        /**
         * Delete objects expiring before a certain date.
         *
         * Succeed if any of the child caches succeed.
         * @param string $date
         * @param bool|callable $progressCallback
         * @return bool
         */
        public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
                $ret = false;
                foreach ( $this->caches as $cache ) {
                        if ( $cache->deleteObjectsExpiringBefore( $date, $progressCallback ) ) {
                                $ret = true;
                        }
                }

                return $ret;
        }
}