LSLockManager.php

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<?php

class LSLockManager extends LockManager {
        protected $lockTypeMap = array(
                self::LOCK_SH => self::LOCK_SH,
                self::LOCK_UW => self::LOCK_SH,
                self::LOCK_EX => self::LOCK_EX
        );

        protected $lockServers; // (server name => server config array)
        protected $srvsByBucket; // (bucket index => (lsrv1, lsrv2, ...))

        protected $conns = array();

        protected $connTimeout; // float number of seconds
        protected $session = ''; // random SHA-1 string

        public function __construct( array $config ) {
                $this->lockServers = $config['lockServers'];
                // Sanitize srvsByBucket config to prevent PHP errors
                $this->srvsByBucket = array_filter( $config['srvsByBucket'], 'is_array' );
                $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive

                if ( isset( $config['connTimeout'] ) ) {
                        $this->connTimeout = $config['connTimeout'];
                } else {
                        $this->connTimeout = 3; // use some sane amount
                }

                $this->session = '';
                for ( $i = 0; $i < 5; $i++ ) {
                        $this->session .= mt_rand( 0, 2147483647 );
                }
                $this->session = wfBaseConvert( sha1( $this->session ), 16, 36, 31 );
        }

        protected function doLock( array $paths, $type ) {
                $status = Status::newGood();

                $pathsToLock = array();
                // Get locks that need to be acquired (buckets => locks)...
                foreach ( $paths as $path ) {
                        if ( isset( $this->locksHeld[$path][$type] ) ) {
                                ++$this->locksHeld[$path][$type];
                        } elseif ( isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
                                $this->locksHeld[$path][$type] = 1;
                        } else {
                                $bucket = $this->getBucketFromKey( $path );
                                $pathsToLock[$bucket][] = $path;
                        }
                }

                $lockedPaths = array(); // files locked in this attempt
                // Attempt to acquire these locks...
                foreach ( $pathsToLock as $bucket => $paths ) {
                        // Try to acquire the locks for this bucket
                        $res = $this->doLockingRequestAll( $bucket, $paths, $type );
                        if ( $res === 'cantacquire' ) {
                                // Resources already locked by another process.
                                // Abort and unlock everything we just locked.
                                foreach ( $paths as $path ) {
                                        $status->fatal( 'lockmanager-fail-acquirelock', $path );
                                }
                                $status->merge( $this->doUnlock( $lockedPaths, $type ) );
                                return $status;
                        } elseif ( $res !== true ) {
                                // Couldn't contact any servers for this bucket.
                                // Abort and unlock everything we just locked.
                                foreach ( $paths as $path ) {
                                        $status->fatal( 'lockmanager-fail-acquirelock', $path );
                                }
                                $status->merge( $this->doUnlock( $lockedPaths, $type ) );
                                return $status;
                        }
                        // Record these locks as active
                        foreach ( $paths as $path ) {
                                $this->locksHeld[$path][$type] = 1; // locked
                        }
                        // Keep track of what locks were made in this attempt
                        $lockedPaths = array_merge( $lockedPaths, $paths );
                }

                return $status;
        }

        protected function doUnlock( array $paths, $type ) {
                $status = Status::newGood();

                foreach ( $paths as $path ) {
                        if ( !isset( $this->locksHeld[$path] ) ) {
                                $status->warning( 'lockmanager-notlocked', $path );
                        } elseif ( !isset( $this->locksHeld[$path][$type] ) ) {
                                $status->warning( 'lockmanager-notlocked', $path );
                        } else {
                                --$this->locksHeld[$path][$type];
                                if ( $this->locksHeld[$path][$type] <= 0 ) {
                                        unset( $this->locksHeld[$path][$type] );
                                }
                                if ( !count( $this->locksHeld[$path] ) ) {
                                        unset( $this->locksHeld[$path] ); // no SH or EX locks left for key
                                }
                        }
                }

                // Reference count the locks held and release locks when zero
                if ( !count( $this->locksHeld ) ) {
                        $status->merge( $this->releaseLocks() );
                }

                return $status;
        }

        protected function doLockingRequest( $lockSrv, array $paths, $type ) {
                if ( $type == self::LOCK_SH ) { // reader locks
                        $type = 'SH';
                } elseif ( $type == self::LOCK_EX ) { // writer locks
                        $type = 'EX';
                } else {
                        return true; // ok...
                }

                // Send out the command and get the response...
                $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
                $response = $this->sendCommand( $lockSrv, 'ACQUIRE', $type, $keys );

                return ( $response === 'ACQUIRED' );
        }

        protected function sendCommand( $lockSrv, $action, $type, $values ) {
                $conn = $this->getConnection( $lockSrv );
                if ( !$conn ) {
                        return false; // no connection
                }
                $authKey = $this->lockServers[$lockSrv]['authKey'];
                // Build of the command as a flat string...
                $values = implode( '|', $values );
                $key = sha1( $this->session . $action . $type . $values . $authKey );
                // Send out the command...
                if ( fwrite( $conn, "{$this->session}:$key:$action:$type:$values\n" ) === false ) {
                        return false;
                }
                // Get the response...
                $response = fgets( $conn );
                if ( $response === false ) {
                        return false;
                }
                return trim( $response );
        }

        protected function doLockingRequestAll( $bucket, array $paths, $type ) {
                $yesVotes = 0; // locks made on trustable servers
                $votesLeft = count( $this->srvsByBucket[$bucket] ); // remaining peers
                $quorum = floor( $votesLeft/2 + 1 ); // simple majority
                // Get votes for each peer, in order, until we have enough...
                foreach ( $this->srvsByBucket[$bucket] as $lockSrv ) {
                        // Attempt to acquire the lock on this peer
                        if ( !$this->doLockingRequest( $lockSrv, $paths, $type ) ) {
                                return 'cantacquire'; // vetoed; resource locked
                        }
                        ++$yesVotes; // success for this peer
                        if ( $yesVotes >= $quorum ) {
                                return true; // lock obtained
                        }
                        --$votesLeft;
                        $votesNeeded = $quorum - $yesVotes;
                        if ( $votesNeeded > $votesLeft ) {
                                // In "trust cache" mode we don't have to meet the quorum
                                break; // short-circuit
                        }
                }
                // At this point, we must not have meet the quorum
                return 'srverrors'; // not enough votes to ensure correctness
        }

        protected function getConnection( $lockSrv ) {
                if ( !isset( $this->conns[$lockSrv] ) ) {
                        $cfg = $this->lockServers[$lockSrv];
                        wfSuppressWarnings();
                        $errno = $errstr = '';
                        $conn = fsockopen( $cfg['host'], $cfg['port'], $errno, $errstr, $this->connTimeout );
                        wfRestoreWarnings();
                        if ( $conn === false ) {
                                return null;
                        }
                        $sec = floor( $this->connTimeout );
                        $usec = floor( ( $this->connTimeout - floor( $this->connTimeout ) ) * 1e6 );
                        stream_set_timeout( $conn, $sec, $usec );
                        $this->conns[$lockSrv] = $conn;
                }
                return $this->conns[$lockSrv];
        }

        protected function releaseLocks() {
                $status = Status::newGood();
                foreach ( $this->conns as $lockSrv => $conn ) {
                        $response = $this->sendCommand( $lockSrv, 'RELEASE_ALL', '', array() );
                        if ( $response !== 'RELEASED_ALL' ) {
                                $status->fatal( 'lockmanager-fail-svr-release', $lockSrv );
                        }
                }
                return $status;
        }

        protected function getBucketFromKey( $path ) {
                $prefix = substr( sha1( $path ), 0, 2 ); // first 2 hex chars (8 bits)
                return intval( base_convert( $prefix, 16, 10 ) ) % count( $this->srvsByBucket );
        }

        function __destruct() {
                $this->releaseLocks();
                foreach ( $this->conns as $conn ) {
                        fclose( $conn );
                }
        }
}