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diff --git a/includes/db/ChronologyProtector.php b/includes/db/ChronologyProtector.php
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+<?php
+/**
+ * Generator of database load balancing 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 Database
+ */
+
+/**
+ * Class for ensuring a consistent ordering of events as seen by the user, despite replication.
+ * Kind of like Hawking's [[Chronology Protection Agency]].
+ */
+class ChronologyProtector {
+	/** @var Array (DB master name => position) */
+	protected $startupPositions = array();
+	/** @var Array (DB master name => position) */
+	protected $shutdownPositions = array();
+
+	protected $initialized = false; // bool; whether the session data was loaded
+
+	/**
+	 * Initialise a LoadBalancer to give it appropriate chronology protection.
+	 *
+	 * If the session has a previous master position recorded, this will try to
+	 * make sure that the next query to a slave of that master will see changes up
+	 * to that position by delaying execution. The delay may timeout and allow stale
+	 * data if no non-lagged slaves are available.
+	 *
+	 * @param $lb LoadBalancer
+	 * @return void
+	 */
+	public function initLB( LoadBalancer $lb ) {
+		if ( $lb->getServerCount() <= 1 ) {
+			return; // non-replicated setup
+		}
+		if ( !$this->initialized ) {
+			$this->initialized = true;
+			if ( isset( $_SESSION[__CLASS__] ) && is_array( $_SESSION[__CLASS__] ) ) {
+				$this->startupPositions = $_SESSION[__CLASS__];
+			}
+		}
+		$masterName = $lb->getServerName( 0 );
+		if ( !empty( $this->startupPositions[$masterName] ) ) {
+			$info = $lb->parentInfo();
+			$pos = $this->startupPositions[$masterName];
+			wfDebug( __METHOD__ . ": LB " . $info['id'] . " waiting for master pos $pos\n" );
+			$lb->waitFor( $pos );
+		}
+	}
+
+	/**
+	 * Notify the ChronologyProtector that the LoadBalancer is about to shut
+	 * down. Saves replication positions.
+	 *
+	 * @param $lb LoadBalancer
+	 * @return void
+	 */
+	public function shutdownLB( LoadBalancer $lb ) {
+		if ( session_id() == '' || $lb->getServerCount() <= 1 ) {
+			return; // don't start a session; don't bother with non-replicated setups
+		}
+		$masterName = $lb->getServerName( 0 );
+		if ( isset( $this->shutdownPositions[$masterName] ) ) {
+			return; // already done
+		}
+		// Only save the position if writes have been done on the connection
+		$db = $lb->getAnyOpenConnection( 0 );
+		$info = $lb->parentInfo();
+		if ( !$db || !$db->doneWrites() ) {
+			wfDebug( __METHOD__ . ": LB {$info['id']}, no writes done\n" );
+			return;
+		}
+		$pos = $db->getMasterPos();
+		wfDebug( __METHOD__ . ": LB {$info['id']} has master pos $pos\n" );
+		$this->shutdownPositions[$masterName] = $pos;
+	}
+
+	/**
+	 * Notify the ChronologyProtector that the LBFactory is done calling shutdownLB() for now.
+	 * May commit chronology data to persistent storage.
+	 *
+	 * @return void
+	 */
+	public function shutdown() {
+		if ( session_id() != '' && count( $this->shutdownPositions ) ) {
+			wfDebug( __METHOD__ . ": saving master pos for " .
+				count( $this->shutdownPositions ) . " master(s)\n" );
+			$_SESSION[__CLASS__] = $this->shutdownPositions;
+		}
+	}
+}