DBLockManager.php

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<?php
abstract class DBLockManager extends QuorumLockManager {
        protected $dbServers; // (DB name => server config array)
        protected $statusCache;

        protected $lockExpiry; // integer number of seconds
        protected $safeDelay; // integer number of seconds

        protected $session = 0; // random integer
        protected $conns = array();

        public function __construct( array $config ) {
                parent::__construct( $config );

                $this->dbServers = isset( $config['dbServers'] )
                        ? $config['dbServers']
                        : array(); // likely just using 'localDBMaster'
                // Sanitize srvsByBucket config to prevent PHP errors
                $this->srvsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
                $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive

                if ( isset( $config['lockExpiry'] ) ) {
                        $this->lockExpiry = $config['lockExpiry'];
                } else {
                        $met = ini_get( 'max_execution_time' );
                        $this->lockExpiry = $met ? $met : 60; // use some sane amount if 0
                }
                $this->safeDelay = ( $this->lockExpiry <= 0 )
                        ? 60 // pick a safe-ish number to match DB timeout default
                        : $this->lockExpiry; // cover worst case

                foreach ( $this->srvsByBucket as $bucket ) {
                        if ( count( $bucket ) > 1 ) { // multiple peers
                                // Tracks peers that couldn't be queried recently to avoid lengthy
                                // connection timeouts. This is useless if each bucket has one peer.
                                try {
                                        $this->statusCache = ObjectCache::newAccelerator( array() );
                                } catch ( MWException $e ) {
                                        trigger_error( __CLASS__ .
                                                " using multiple DB peers without apc, xcache, or wincache." );
                                }
                                break;
                        }
                }

                $this->session = wfRandomString( 31 );
        }

        protected function isServerUp( $lockSrv ) {
                if ( !$this->cacheCheckFailures( $lockSrv ) ) {
                        return false; // recent failure to connect
                }
                try {
                        $this->getConnection( $lockSrv );
                } catch ( DBError $e ) {
                        $this->cacheRecordFailure( $lockSrv );
                        return false; // failed to connect
                }
                return true;
        }

        protected function getConnection( $lockDb ) {
                if ( !isset( $this->conns[$lockDb] ) ) {
                        $db = null;
                        if ( $lockDb === 'localDBMaster' ) {
                                $lb = wfGetLBFactory()->getMainLB( $this->domain );
                                $db = $lb->getConnection( DB_MASTER, array(), $this->domain );
                        } elseif ( isset( $this->dbServers[$lockDb] ) ) {
                                $config = $this->dbServers[$lockDb];
                                $db = DatabaseBase::factory( $config['type'], $config );
                        }
                        if ( !$db ) {
                                return null; // config error?
                        }
                        $this->conns[$lockDb] = $db;
                        $this->conns[$lockDb]->clearFlag( DBO_TRX );
                        # If the connection drops, try to avoid letting the DB rollback
                        # and release the locks before the file operations are finished.
                        # This won't handle the case of DB server restarts however.
                        $options = array();
                        if ( $this->lockExpiry > 0 ) {
                                $options['connTimeout'] = $this->lockExpiry;
                        }
                        $this->conns[$lockDb]->setSessionOptions( $options );
                        $this->initConnection( $lockDb, $this->conns[$lockDb] );
                }
                if ( !$this->conns[$lockDb]->trxLevel() ) {
                        $this->conns[$lockDb]->begin( __METHOD__ ); // start transaction
                }
                return $this->conns[$lockDb];
        }

        protected function initConnection( $lockDb, DatabaseBase $db ) {}

        protected function cacheCheckFailures( $lockDb ) {
                return ( $this->statusCache && $this->safeDelay > 0 )
                        ? !$this->statusCache->get( $this->getMissKey( $lockDb ) )
                        : true;
        }

        protected function cacheRecordFailure( $lockDb ) {
                return ( $this->statusCache && $this->safeDelay > 0 )
                        ? $this->statusCache->set( $this->getMissKey( $lockDb ), 1, $this->safeDelay )
                        : true;
        }

        protected function getMissKey( $lockDb ) {
                $lockDb = ( $lockDb === 'localDBMaster' ) ? wfWikiID() : $lockDb; // non-relative
                return 'dblockmanager:downservers:' . str_replace( ' ', '_', $lockDb );
        }

        function __destruct() {
                $this->releaseAllLocks();
                foreach ( $this->conns as $db ) {
                        $db->close();
                }
        }
}

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

        protected function initConnection( $lockDb, DatabaseBase $db ) {
                # Let this transaction see lock rows from other transactions
                $db->query( "SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;" );
        }

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

                $db = $this->getConnection( $lockSrv ); // checked in isServerUp()

                $keys = array(); // list of hash keys for the paths
                $data = array(); // list of rows to insert
                $checkEXKeys = array(); // list of hash keys that this has no EX lock on
                # Build up values for INSERT clause
                foreach ( $paths as $path ) {
                        $key = $this->sha1Base36Absolute( $path );
                        $keys[] = $key;
                        $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
                        if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
                                $checkEXKeys[] = $key;
                        }
                }

                # Block new writers (both EX and SH locks leave entries here)...
                $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
                # Actually do the locking queries...
                if ( $type == self::LOCK_SH ) { // reader locks
                        $blocked = false;
                        # Bail if there are any existing writers...
                        if ( count( $checkEXKeys ) ) {
                                $blocked = $db->selectField( 'filelocks_exclusive', '1',
                                        array( 'fle_key' => $checkEXKeys ),
                                        __METHOD__
                                );
                        }
                        # Other prospective writers that haven't yet updated filelocks_exclusive
                        # will recheck filelocks_shared after doing so and bail due to this entry.
                } else { // writer locks
                        $encSession = $db->addQuotes( $this->session );
                        # Bail if there are any existing writers...
                        # This may detect readers, but the safe check for them is below.
                        # Note: if two writers come at the same time, both bail :)
                        $blocked = $db->selectField( 'filelocks_shared', '1',
                                array( 'fls_key' => $keys, "fls_session != $encSession" ),
                                __METHOD__
                        );
                        if ( !$blocked ) {
                                # Build up values for INSERT clause
                                $data = array();
                                foreach ( $keys as $key ) {
                                        $data[] = array( 'fle_key' => $key );
                                }
                                # Block new readers/writers...
                                $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
                                # Bail if there are any existing readers...
                                $blocked = $db->selectField( 'filelocks_shared', '1',
                                        array( 'fls_key' => $keys, "fls_session != $encSession" ),
                                        __METHOD__
                                );
                        }
                }

                if ( $blocked ) {
                        foreach ( $paths as $path ) {
                                $status->fatal( 'lockmanager-fail-acquirelock', $path );
                        }
                }

                return $status;
        }

        protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
                return Status::newGood(); // not supported
        }

        protected function releaseAllLocks() {
                $status = Status::newGood();

                foreach ( $this->conns as $lockDb => $db ) {
                        if ( $db->trxLevel() ) { // in transaction
                                try {
                                        $db->rollback( __METHOD__ ); // finish transaction and kill any rows
                                } catch ( DBError $e ) {
                                        $status->fatal( 'lockmanager-fail-db-release', $lockDb );
                                }
                        }
                }

                return $status;
        }
}

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

        protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
                $status = Status::newGood();
                if ( !count( $paths ) ) {
                        return $status; // nothing to lock
                }

                $db = $this->getConnection( $lockSrv ); // checked in isServerUp()
                $bigints = array_unique( array_map(
                        function( $key ) { return wfBaseConvert( substr( $key, 0, 15 ), 16, 10 ); },
                        array_map( array( $this, 'sha1Base16Absolute' ), $paths )
                ) );

                // Try to acquire all the locks...
                $fields = array();
                foreach ( $bigints as $bigint ) {
                        $fields[] = ( $type == self::LOCK_SH )
                                ? "pg_try_advisory_lock_shared({$db->addQuotes( $bigint )}) AS K$bigint"
                                : "pg_try_advisory_lock({$db->addQuotes( $bigint )}) AS K$bigint";
                }
                $res = $db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
                $row = (array)$res->fetchObject();

                if ( in_array( 'f', $row ) ) {
                        // Release any acquired locks if some could not be acquired...
                        $fields = array();
                        foreach ( $row as $kbigint => $ok ) {
                                if ( $ok === 't' ) { // locked
                                        $bigint = substr( $kbigint, 1 ); // strip off the "K"
                                        $fields[] = ( $type == self::LOCK_SH )
                                                ? "pg_advisory_unlock_shared({$db->addQuotes( $bigint )})"
                                                : "pg_advisory_unlock({$db->addQuotes( $bigint )})";
                                }
                        }
                        if ( count( $fields ) ) {
                                $db->query( 'SELECT ' . implode( ', ', $fields ), __METHOD__ );
                        }
                        foreach ( $paths as $path ) {
                                $status->fatal( 'lockmanager-fail-acquirelock', $path );
                        }
                }

                return $status;
        }

        protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
                return Status::newGood(); // not supported
        }

        protected function releaseAllLocks() {
                $status = Status::newGood();

                foreach ( $this->conns as $lockDb => $db ) {
                        try {
                                $db->query( "SELECT pg_advisory_unlock_all()", __METHOD__ );
                        } catch ( DBError $e ) {
                                $status->fatal( 'lockmanager-fail-db-release', $lockDb );
                        }
                }

                return $status;
        }
}