--- /dev/null
+<?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 );
+ }
+ }
+ }
+}
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