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diff --git a/www/wiki/includes/libs/objectcache/MultiWriteBagOStuff.php b/www/wiki/includes/libs/objectcache/MultiWriteBagOStuff.php
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+++ b/www/wiki/includes/libs/objectcache/MultiWriteBagOStuff.php
@@ -0,0 +1,244 @@
+<?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
+ */
+use Wikimedia\ObjectFactory;
+
+/**
+ * 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 int $count
+	 * @param bool $asyncWrites
+	 * @param string $method
+	 * @param mixed $args,...
+	 * @return bool
+	 */
+	protected function doWrite( $count, $asyncWrites, $method /*, ... */ ) {
+		$ret = true;
+		$args = array_slice( func_get_args(), 3 );
+
+		if ( $count > 1 && $asyncWrites ) {
+			// Deep-clone $args to prevent misbehavior when something writes an
+			// object to the BagOStuff then modifies it afterwards, e.g. T168040.
+			$args = unserialize( serialize( $args ) );
+		}
+
+		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;
+	}
+
+	public function makeKey( $class, $component = null ) {
+		return call_user_func_array( [ $this->caches[0], __FUNCTION__ ], func_get_args() );
+	}
+
+	public function makeGlobalKey( $class, $component = null ) {
+		return call_user_func_array( [ $this->caches[0], __FUNCTION__ ], func_get_args() );
+	}
+}