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[mediawiki.git] / includes / libs / lockmanager / MemcLockManager.php

<?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' ]; // default

                $class = $memcConfig['class'];
                if ( !is_subclass_of( $class, 'MemcachedBagOStuff' ) ) {
                        throw new InvalidArgumentException( "$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 );
                        }
                }
        }
}