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+<?php
+
+/**
+ * Version of LockManager based on using DB table locks.
+ * This is meant for multi-wiki systems that may share files.
+ * All locks are blocking, so it might be useful to set a small
+ * lock-wait timeout via server config to curtail 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 DBs, each on their
+ * own server, all having the filelocks.sql tables (with row-level locking).
+ * A majority of peer DBs must agree for a lock to be acquired.
+ *
+ * Caching is used to avoid hitting servers that are down.
+ *
+ * @ingroup LockManager
+ * @since 1.19
+ */
+class DBLockManager extends LockManager {
+ /** @var Array Map of DB names to server config */
+ protected $dbServers; // (DB name => server config array)
+ /** @var Array Map of bucket indexes to peer DB lists */
+ protected $dbsByBucket; // (bucket index => (ldb1, ldb2, ...))
+ /** @var BagOStuff */
+ protected $statusCache;
+
+ protected $lockExpiry; // integer number of seconds
+ protected $safeDelay; // integer number of seconds
+
+ protected $session = 0; // random integer
+ /** @var Array Map Database connections (DB name => Database) */
+ protected $conns = array();
+
+ /**
+ * Construct a new instance from configuration.
+ *
+ * $config paramaters include:
+ * 'dbServers' : Associative array of DB names to server configuration.
+ * Configuration is an associative array that includes:
+ * 'host' - DB server name
+ * 'dbname' - DB name
+ * 'type' - DB type (mysql,postgres,...)
+ * 'user' - DB user
+ * 'password' - DB user password
+ * 'tablePrefix' - DB table prefix
+ * 'flags' - DB flags (see DatabaseBase)
+ * 'dbsByBucket' : Array of 1-16 consecutive integer keys, starting from 0,
+ * each having an odd-numbered list of DB names (peers) as values.
+ * Any DB named 'localDBMaster' will automatically use the DB master
+ * settings for this wiki (without the need for a dbServers entry).
+ * 'lockExpiry' : Lock timeout (seconds) for dropped connections. [optional]
+ * This tells the DB server how long to wait before assuming
+ * connection failure and releasing all the locks for a session.
+ *
+ * @param Array $config
+ */
+ public function __construct( array $config ) {
+ $this->dbServers = isset( $config['dbServers'] )
+ ? $config['dbServers']
+ : array(); // likely just using 'localDBMaster'
+ // Sanitize dbsByBucket config to prevent PHP errors
+ $this->dbsByBucket = array_filter( $config['dbsByBucket'], 'is_array' );
+ $this->dbsByBucket = array_values( $this->dbsByBucket ); // 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->dbsByBucket as $bucket ) {
+ if ( count( $bucket ) > 1 ) {
+ // Tracks peers that couldn't be queried recently to avoid lengthy
+ // connection timeouts. This is useless if each bucket has one peer.
+ $this->statusCache = wfGetMainCache();
+ break;
+ }
+ }
+
+ $this->session = '';
+ for ( $i = 0; $i < 5; $i++ ) {
+ $this->session .= mt_rand( 0, 2147483647 );
+ }
+ $this->session = wfBaseConvert( sha1( $this->session ), 16, 36, 31 );
+ }
+
+ /**
+ * @see LockManager::doLock()
+ */
+ 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->doLockingQueryAll( $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 DBs for this bucket.
+ // Abort and unlock everything we just locked.
+ $status->fatal( 'lockmanager-fail-db-bucket', $bucket );
+ $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;
+ }
+
+ /**
+ * @see LockManager::doUnlock()
+ */
+ 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 COMMIT when zero
+ if ( !count( $this->locksHeld ) ) {
+ $status->merge( $this->finishLockTransactions() );
+ }
+
+ return $status;
+ }
+
+ /**
+ * Get a connection to a lock DB and acquire locks on $paths.
+ * This does not use GET_LOCK() per http://bugs.mysql.com/bug.php?id=1118.
+ *
+ * @param $lockDb string
+ * @param $paths Array
+ * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
+ * @return bool Resources able to be locked
+ * @throws DBError
+ */
+ protected function doLockingQuery( $lockDb, array $paths, $type ) {
+ if ( $type == self::LOCK_EX ) { // writer locks
+ $db = $this->getConnection( $lockDb );
+ if ( !$db ) {
+ return false; // bad config
+ }
+ $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
+ # Build up values for INSERT clause
+ $data = array();
+ foreach ( $keys as $key ) {
+ $data[] = array( 'fle_key' => $key );
+ }
+ # Wait on any existing writers and block new ones if we get in
+ $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
+ }
+ return true;
+ }
+
+ /**
+ * Attempt to acquire locks with the peers for a bucket.
+ * This should avoid throwing any exceptions.
+ *
+ * @param $bucket integer
+ * @param $paths Array List of resource keys to lock
+ * @param $type integer LockManager::LOCK_EX or LockManager::LOCK_SH
+ * @return bool|string One of (true, 'cantacquire', 'dberrors')
+ */
+ protected function doLockingQueryAll( $bucket, array $paths, $type ) {
+ $yesVotes = 0; // locks made on trustable DBs
+ $votesLeft = count( $this->dbsByBucket[$bucket] ); // remaining DBs
+ $quorum = floor( $votesLeft/2 + 1 ); // simple majority
+ // Get votes for each DB, in order, until we have enough...
+ foreach ( $this->dbsByBucket[$bucket] as $lockDb ) {
+ // Check that DB is not *known* to be down
+ if ( $this->cacheCheckFailures( $lockDb ) ) {
+ try {
+ // Attempt to acquire the lock on this DB
+ if ( !$this->doLockingQuery( $lockDb, $paths, $type ) ) {
+ return 'cantacquire'; // vetoed; resource locked
+ }
+ ++$yesVotes; // success for this peer
+ if ( $yesVotes >= $quorum ) {
+ return true; // lock obtained
+ }
+ } catch ( DBConnectionError $e ) {
+ $this->cacheRecordFailure( $lockDb );
+ } catch ( DBError $e ) {
+ if ( $this->lastErrorIndicatesLocked( $lockDb ) ) {
+ return 'cantacquire'; // vetoed; resource locked
+ }
+ }
+ }
+ --$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 'dberrors'; // not enough votes to ensure correctness
+ }
+
+ /**
+ * Get (or reuse) a connection to a lock DB
+ *
+ * @param $lockDb string
+ * @return Database
+ * @throws DBError
+ */
+ protected function getConnection( $lockDb ) {
+ if ( !isset( $this->conns[$lockDb] ) ) {
+ $db = null;
+ if ( $lockDb === 'localDBMaster' ) {
+ $lb = wfGetLBFactory()->newMainLB();
+ $db = $lb->getConnection( DB_MASTER );
+ } 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(); // start transaction
+ }
+ return $this->conns[$lockDb];
+ }
+
+ /**
+ * Do additional initialization for new lock DB connection
+ *
+ * @param $lockDb string
+ * @param $db DatabaseBase
+ * @return void
+ * @throws DBError
+ */
+ protected function initConnection( $lockDb, DatabaseBase $db ) {}
+
+ /**
+ * Commit all changes to lock-active databases.
+ * This should avoid throwing any exceptions.
+ *
+ * @return Status
+ */
+ protected function finishLockTransactions() {
+ $status = Status::newGood();
+ foreach ( $this->conns as $lockDb => $db ) {
+ if ( $db->trxLevel() ) { // in transaction
+ try {
+ $db->rollback(); // finish transaction and kill any rows
+ } catch ( DBError $e ) {
+ $status->fatal( 'lockmanager-fail-db-release', $lockDb );
+ }
+ }
+ }
+ return $status;
+ }
+
+ /**
+ * Check if the last DB error for $lockDb indicates
+ * that a requested resource was locked by another process.
+ * This should avoid throwing any exceptions.
+ *
+ * @param $lockDb string
+ * @return bool
+ */
+ protected function lastErrorIndicatesLocked( $lockDb ) {
+ if ( isset( $this->conns[$lockDb] ) ) { // sanity
+ $db = $this->conns[$lockDb];
+ return ( $db->wasDeadlock() || $db->wasLockTimeout() );
+ }
+ return false;
+ }
+
+ /**
+ * Checks if the DB has not recently had connection/query errors.
+ * This just avoids wasting time on doomed connection attempts.
+ *
+ * @param $lockDb string
+ * @return bool
+ */
+ protected function cacheCheckFailures( $lockDb ) {
+ if ( $this->statusCache && $this->safeDelay > 0 ) {
+ $path = $this->getMissKey( $lockDb );
+ $misses = $this->statusCache->get( $path );
+ return !$misses;
+ }
+ return true;
+ }
+
+ /**
+ * Log a lock request failure to the cache
+ *
+ * @param $lockDb string
+ * @return bool Success
+ */
+ protected function cacheRecordFailure( $lockDb ) {
+ if ( $this->statusCache && $this->safeDelay > 0 ) {
+ $path = $this->getMissKey( $lockDb );
+ $misses = $this->statusCache->get( $path );
+ if ( $misses ) {
+ return $this->statusCache->incr( $path );
+ } else {
+ return $this->statusCache->add( $path, 1, $this->safeDelay );
+ }
+ }
+ return true;
+ }
+
+ /**
+ * Get a cache key for recent query misses for a DB
+ *
+ * @param $lockDb string
+ * @return string
+ */
+ protected function getMissKey( $lockDb ) {
+ return 'lockmanager:querymisses:' . str_replace( ' ', '_', $lockDb );
+ }
+
+ /**
+ * Get the bucket for resource path.
+ * This should avoid throwing any exceptions.
+ *
+ * @param $path string
+ * @return integer
+ */
+ 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->dbsByBucket );
+ }
+
+ /**
+ * Make sure remaining locks get cleared for sanity
+ */
+ function __destruct() {
+ foreach ( $this->conns as $lockDb => $db ) {
+ if ( $db->trxLevel() ) { // in transaction
+ try {
+ $db->rollback(); // finish transaction and kill any rows
+ } catch ( DBError $e ) {
+ // oh well
+ }
+ }
+ $db->close();
+ }
+ }
+}
+
+/**
+ * MySQL version of DBLockManager that supports shared locks.
+ * All locks are non-blocking, which avoids deadlocks.
+ *
+ * @ingroup LockManager
+ */
+class MySqlLockManager extends DBLockManager {
+ /** @var Array Mapping of lock types to the type actually used */
+ 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 doLockingQuery( $lockDb, array $paths, $type ) {
+ $db = $this->getConnection( $lockDb );
+ if ( !$db ) {
+ return false;
+ }
+ $keys = array_unique( array_map( 'LockManager::sha1Base36', $paths ) );
+ # Build up values for INSERT clause
+ $data = array();
+ foreach ( $keys as $key ) {
+ $data[] = array( 'fls_key' => $key, 'fls_session' => $this->session );
+ }
+ # Block new writers...
+ $db->insert( 'filelocks_shared', $data, __METHOD__, array( 'IGNORE' ) );
+ # Actually do the locking queries...
+ if ( $type == self::LOCK_SH ) { // reader locks
+ # Bail if there are any existing writers...
+ $blocked = $db->selectField( 'filelocks_exclusive', '1',
+ array( 'fle_key' => $keys ),
+ __METHOD__
+ );
+ # Prospective writers that haven't yet updated filelocks_exclusive
+ # will recheck filelocks_shared after doing so and bail due to our entry.
+ } else { // writer locks
+ $encSession = $db->addQuotes( $this->session );
+ # Bail if there are any existing writers...
+ # The 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 != $encSession" ),
+ __METHOD__
+ );
+ }
+ }
+ return !$blocked;
+ }
+}
generated by cgit v1.2.2 (git 2.25.0) at 2024-04-25 00:59:51 +0000