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diff --git a/www/wiki/includes/libs/lockmanager/MemcLockManager.php b/www/wiki/includes/libs/lockmanager/MemcLockManager.php
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+++ b/www/wiki/includes/libs/lockmanager/MemcLockManager.php
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+<?php
+/**
+ * Version of LockManager based on using memcached servers.
+ *
+ * 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 LockManager
+ */
+use Wikimedia\WaitConditionLoop;
+
+/**
+ * Manage locks using memcached servers.
+ *
+ * Version of LockManager based on using memcached servers.
+ * This is meant for multi-wiki systems that may share files.
+ * All locks are non-blocking, which avoids deadlocks.
+ *
+ * All lock requests for a resource, identified by a hash string, will map to one
+ * bucket. Each bucket maps to one or several peer servers, each running memcached.
+ * A majority of peers must agree for a lock to be acquired.
+ *
+ * @ingroup LockManager
+ * @since 1.20
+ */
+class MemcLockManager extends QuorumLockManager {
+	/** @var array Mapping of lock types to the type actually used */
+	protected $lockTypeMap = [
+		self::LOCK_SH => self::LOCK_SH,
+		self::LOCK_UW => self::LOCK_SH,
+		self::LOCK_EX => self::LOCK_EX
+	];
+
+	/** @var MemcachedBagOStuff[] Map of (server name => MemcachedBagOStuff) */
+	protected $cacheServers = [];
+	/** @var HashBagOStuff Server status cache */
+	protected $statusCache;
+
+	/**
+	 * Construct a new instance from configuration.
+	 *
+	 * @param array $config Parameters include:
+	 *   - lockServers  : Associative array of server names to "<IP>:<port>" strings.
+	 *   - srvsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
+	 *                    each having an odd-numbered list of server names (peers) as values.
+	 *   - memcConfig   : Configuration array for MemcachedBagOStuff::construct() with an
+	 *                    additional 'class' parameter specifying which MemcachedBagOStuff
+	 *                    subclass to use. The server names will be injected. [optional]
+	 * @throws Exception
+	 */
+	public function __construct( array $config ) {
+		parent::__construct( $config );
+
+		// Sanitize srvsByBucket config to prevent PHP errors
+		$this->srvsByBucket = array_filter( $config['srvsByBucket'], 'is_array' );
+		$this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
+
+		$memcConfig = isset( $config['memcConfig'] ) ? $config['memcConfig'] : [];
+		$memcConfig += [ 'class' => MemcachedPhpBagOStuff::class ]; // default
+
+		$class = $memcConfig['class'];
+		if ( !is_subclass_of( $class, MemcachedBagOStuff::class ) ) {
+			throw new InvalidArgumentException( "$class is not of type MemcachedBagOStuff." );
+		}
+
+		foreach ( $config['lockServers'] as $name => $address ) {
+			$params = [ 'servers' => [ $address ] ] + $memcConfig;
+			$this->cacheServers[$name] = new $class( $params );
+		}
+
+		$this->statusCache = new HashBagOStuff();
+	}
+
+	protected function getLocksOnServer( $lockSrv, array $pathsByType ) {
+		$status = StatusValue::newGood();
+
+		$memc = $this->getCache( $lockSrv );
+		// List of affected paths
+		$paths = call_user_func_array( 'array_merge', array_values( $pathsByType ) );
+		$paths = array_unique( $paths );
+		// List of affected lock record keys
+		$keys = array_map( [ $this, 'recordKeyForPath' ], $paths );
+
+		// Lock all of the active lock record keys...
+		if ( !$this->acquireMutexes( $memc, $keys ) ) {
+			foreach ( $paths as $path ) {
+				$status->fatal( 'lockmanager-fail-acquirelock', $path );
+			}
+
+			return $status;
+		}
+
+		// Fetch all the existing lock records...
+		$lockRecords = $memc->getMulti( $keys );
+
+		$now = time();
+		// Check if the requested locks conflict with existing ones...
+		foreach ( $pathsByType as $type => $paths ) {
+			foreach ( $paths as $path ) {
+				$locksKey = $this->recordKeyForPath( $path );
+				$locksHeld = isset( $lockRecords[$locksKey] )
+					? self::sanitizeLockArray( $lockRecords[$locksKey] )
+					: self::newLockArray(); // init
+				foreach ( $locksHeld[self::LOCK_EX] as $session => $expiry ) {
+					if ( $expiry < $now ) { // stale?
+						unset( $locksHeld[self::LOCK_EX][$session] );
+					} elseif ( $session !== $this->session ) {
+						$status->fatal( 'lockmanager-fail-acquirelock', $path );
+					}
+				}
+				if ( $type === self::LOCK_EX ) {
+					foreach ( $locksHeld[self::LOCK_SH] as $session => $expiry ) {
+						if ( $expiry < $now ) { // stale?
+							unset( $locksHeld[self::LOCK_SH][$session] );
+						} elseif ( $session !== $this->session ) {
+							$status->fatal( 'lockmanager-fail-acquirelock', $path );
+						}
+					}
+				}
+				if ( $status->isOK() ) {
+					// Register the session in the lock record array
+					$locksHeld[$type][$this->session] = $now + $this->lockTTL;
+					// We will update this record if none of the other locks conflict
+					$lockRecords[$locksKey] = $locksHeld;
+				}
+			}
+		}
+
+		// If there were no lock conflicts, update all the lock records...
+		if ( $status->isOK() ) {
+			foreach ( $paths as $path ) {
+				$locksKey = $this->recordKeyForPath( $path );
+				$locksHeld = $lockRecords[$locksKey];
+				$ok = $memc->set( $locksKey, $locksHeld, self::MAX_LOCK_TTL );
+				if ( !$ok ) {
+					$status->fatal( 'lockmanager-fail-acquirelock', $path );
+				} else {
+					$this->logger->debug( __METHOD__ . ": acquired lock on key $locksKey.\n" );
+				}
+			}
+		}
+
+		// Unlock all of the active lock record keys...
+		$this->releaseMutexes( $memc, $keys );
+
+		return $status;
+	}
+
+	protected function freeLocksOnServer( $lockSrv, array $pathsByType ) {
+		$status = StatusValue::newGood();
+
+		$memc = $this->getCache( $lockSrv );
+		// List of affected paths
+		$paths = call_user_func_array( 'array_merge', array_values( $pathsByType ) );
+		$paths = array_unique( $paths );
+		// List of affected lock record keys
+		$keys = array_map( [ $this, 'recordKeyForPath' ], $paths );
+
+		// Lock all of the active lock record keys...
+		if ( !$this->acquireMutexes( $memc, $keys ) ) {
+			foreach ( $paths as $path ) {
+				$status->fatal( 'lockmanager-fail-releaselock', $path );
+			}
+
+			return $status;
+		}
+
+		// Fetch all the existing lock records...
+		$lockRecords = $memc->getMulti( $keys );
+
+		// Remove the requested locks from all records...
+		foreach ( $pathsByType as $type => $paths ) {
+			foreach ( $paths as $path ) {
+				$locksKey = $this->recordKeyForPath( $path ); // lock record
+				if ( !isset( $lockRecords[$locksKey] ) ) {
+					$status->warning( 'lockmanager-fail-releaselock', $path );
+					continue; // nothing to do
+				}
+				$locksHeld = $this->sanitizeLockArray( $lockRecords[$locksKey] );
+				if ( isset( $locksHeld[$type][$this->session] ) ) {
+					unset( $locksHeld[$type][$this->session] ); // unregister this session
+					$lockRecords[$locksKey] = $locksHeld;
+				} else {
+					$status->warning( 'lockmanager-fail-releaselock', $path );
+				}
+			}
+		}
+
+		// Persist the new lock record values...
+		foreach ( $paths as $path ) {
+			$locksKey = $this->recordKeyForPath( $path );
+			if ( !isset( $lockRecords[$locksKey] ) ) {
+				continue; // nothing to do
+			}
+			$locksHeld = $lockRecords[$locksKey];
+			if ( $locksHeld === $this->newLockArray() ) {
+				$ok = $memc->delete( $locksKey );
+			} else {
+				$ok = $memc->set( $locksKey, $locksHeld, self::MAX_LOCK_TTL );
+			}
+			if ( $ok ) {
+				$this->logger->debug( __METHOD__ . ": released lock on key $locksKey.\n" );
+			} else {
+				$status->fatal( 'lockmanager-fail-releaselock', $path );
+			}
+		}
+
+		// Unlock all of the active lock record keys...
+		$this->releaseMutexes( $memc, $keys );
+
+		return $status;
+	}
+
+	/**
+	 * @see QuorumLockManager::releaseAllLocks()
+	 * @return StatusValue
+	 */
+	protected function releaseAllLocks() {
+		return StatusValue::newGood(); // not supported
+	}
+
+	/**
+	 * @see QuorumLockManager::isServerUp()
+	 * @param string $lockSrv
+	 * @return bool
+	 */
+	protected function isServerUp( $lockSrv ) {
+		return (bool)$this->getCache( $lockSrv );
+	}
+
+	/**
+	 * Get the MemcachedBagOStuff object for a $lockSrv
+	 *
+	 * @param string $lockSrv Server name
+	 * @return MemcachedBagOStuff|null
+	 */
+	protected function getCache( $lockSrv ) {
+		if ( !isset( $this->cacheServers[$lockSrv] ) ) {
+			throw new InvalidArgumentException( "Invalid cache server '$lockSrv'." );
+		}
+
+		$online = $this->statusCache->get( "online:$lockSrv" );
+		if ( $online === false ) {
+			$online = $this->cacheServers[$lockSrv]->set( __CLASS__ . ':ping', 1, 1 );
+			if ( !$online ) { // server down?
+				$this->logger->warning( __METHOD__ . ": Could not contact $lockSrv." );
+			}
+			$this->statusCache->set( "online:$lockSrv", (int)$online, 30 );
+		}
+
+		return $online ? $this->cacheServers[$lockSrv] : null;
+	}
+
+	/**
+	 * @param string $path
+	 * @return string
+	 */
+	protected function recordKeyForPath( $path ) {
+		return implode( ':', [ __CLASS__, 'locks', $this->sha1Base36Absolute( $path ) ] );
+	}
+
+	/**
+	 * @return array An empty lock structure for a key
+	 */
+	protected function newLockArray() {
+		return [ self::LOCK_SH => [], self::LOCK_EX => [] ];
+	}
+
+	/**
+	 * @param array $a
+	 * @return array An empty lock structure for a key
+	 */
+	protected function sanitizeLockArray( $a ) {
+		if ( is_array( $a ) && isset( $a[self::LOCK_EX] ) && isset( $a[self::LOCK_SH] ) ) {
+			return $a;
+		}
+
+		$this->logger->error( __METHOD__ . ": reset invalid lock array." );
+
+		return $this->newLockArray();
+	}
+
+	/**
+	 * @param MemcachedBagOStuff $memc
+	 * @param array $keys List of keys to acquire
+	 * @return bool
+	 */
+	protected function acquireMutexes( MemcachedBagOStuff $memc, array $keys ) {
+		$lockedKeys = [];
+
+		// Acquire the keys in lexicographical order, to avoid deadlock problems.
+		// If P1 is waiting to acquire a key P2 has, P2 can't also be waiting for a key P1 has.
+		sort( $keys );
+
+		// Try to quickly loop to acquire the keys, but back off after a few rounds.
+		// This reduces memcached spam, especially in the rare case where a server acquires
+		// some lock keys and dies without releasing them. Lock keys expire after a few minutes.
+		$loop = new WaitConditionLoop(
+			function () use ( $memc, $keys, &$lockedKeys ) {
+				foreach ( array_diff( $keys, $lockedKeys ) as $key ) {
+					if ( $memc->add( "$key:mutex", 1, 180 ) ) { // lock record
+						$lockedKeys[] = $key;
+					}
+				}
+
+				return array_diff( $keys, $lockedKeys )
+					? WaitConditionLoop::CONDITION_CONTINUE
+					: true;
+			},
+			3.0 // timeout
+		);
+		$loop->invoke();
+
+		if ( count( $lockedKeys ) != count( $keys ) ) {
+			$this->releaseMutexes( $memc, $lockedKeys ); // failed; release what was locked
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * @param MemcachedBagOStuff $memc
+	 * @param array $keys List of acquired keys
+	 */
+	protected function releaseMutexes( MemcachedBagOStuff $memc, array $keys ) {
+		foreach ( $keys as $key ) {
+			$memc->delete( "$key:mutex" );
+		}
+	}
+
+	/**
+	 * Make sure remaining locks get cleared for sanity
+	 */
+	function __destruct() {
+		while ( count( $this->locksHeld ) ) {
+			foreach ( $this->locksHeld as $path => $locks ) {
+				$this->doUnlock( [ $path ], self::LOCK_EX );
+				$this->doUnlock( [ $path ], self::LOCK_SH );
+			}
+		}
+	}
+}