-<?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
- */
-
-/**
- * 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 array Map server names to MemcachedBagOStuff objects */
- protected $bagOStuffs = [];
-
- /** @var array (server name => bool) */
- protected $serversUp = [];
-
- /** @var string Random UUID */
- protected $session = '';
-
- /**
- * 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 ObjectCache::newFromParams. [optional]
- * If set, this must use one of the memcached classes.
- * @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']
- : [ 'class' => 'MemcachedPhpBagOStuff' ];
-
- foreach ( $config['lockServers'] as $name => $address ) {
- $params = [ 'servers' => [ $address ] ] + $memcConfig;
- $cache = ObjectCache::newFromParams( $params );
- if ( $cache instanceof MemcachedBagOStuff ) {
- $this->bagOStuffs[$name] = $cache;
- } else {
- throw new Exception(
- 'Only MemcachedBagOStuff classes are supported by MemcLockManager.' );
- }
- }
-
- $this->session = wfRandomString( 32 );
- }
-
- // @todo Change this code to work in one batch
- protected function getLocksOnServer( $lockSrv, array $pathsByType ) {
- $status = StatusValue::newGood();
-
- $lockedPaths = [];
- foreach ( $pathsByType as $type => $paths ) {
- $status->merge( $this->doGetLocksOnServer( $lockSrv, $paths, $type ) );
- if ( $status->isOK() ) {
- $lockedPaths[$type] = isset( $lockedPaths[$type] )
- ? array_merge( $lockedPaths[$type], $paths )
- : $paths;
- } else {
- foreach ( $lockedPaths as $lType => $lPaths ) {
- $status->merge( $this->doFreeLocksOnServer( $lockSrv, $lPaths, $lType ) );
- }
- break;
- }
- }
-
- return $status;
- }
-
- // @todo Change this code to work in one batch
- protected function freeLocksOnServer( $lockSrv, array $pathsByType ) {
- $status = StatusValue::newGood();
-
- foreach ( $pathsByType as $type => $paths ) {
- $status->merge( $this->doFreeLocksOnServer( $lockSrv, $paths, $type ) );
- }
-
- return $status;
- }
-
- /**
- * @see QuorumLockManager::getLocksOnServer()
- * @param string $lockSrv
- * @param array $paths
- * @param string $type
- * @return StatusValue
- */
- protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
- $status = StatusValue::newGood();
-
- $memc = $this->getCache( $lockSrv );
- $keys = array_map( [ $this, 'recordKeyForPath' ], $paths ); // lock records
-
- // Lock all of the active lock record keys...
- if ( !$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 ( $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, $locksHeld, 7 * 86400 );
- if ( !$ok ) {
- $status->fatal( 'lockmanager-fail-acquirelock', $path );
- } else {
- wfDebug( __METHOD__ . ": acquired lock on key $locksKey.\n" );
- }
- }
- }
-
- // Unlock all of the active lock record keys...
- $this->releaseMutexes( $memc, $keys );
-
- return $status;
- }
-
- /**
- * @see QuorumLockManager::freeLocksOnServer()
- * @param string $lockSrv
- * @param array $paths
- * @param string $type
- * @return StatusValue
- */
- protected function doFreeLocksOnServer( $lockSrv, array $paths, $type ) {
- $status = StatusValue::newGood();
-
- $memc = $this->getCache( $lockSrv );
- $keys = array_map( [ $this, 'recordKeyForPath' ], $paths ); // lock records
-
- // Lock all of the active lock record keys...
- if ( !$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 ( $paths as $path ) {
- $locksKey = $this->recordKeyForPath( $path ); // lock record
- if ( !isset( $lockRecords[$locksKey] ) ) {
- $status->warning( 'lockmanager-fail-releaselock', $path );
- continue; // nothing to do
- }
- $locksHeld = self::sanitizeLockArray( $lockRecords[$locksKey] );
- if ( isset( $locksHeld[$type][$this->session] ) ) {
- unset( $locksHeld[$type][$this->session] ); // unregister this session
- if ( $locksHeld === self::newLockArray() ) {
- $ok = $memc->delete( $locksKey );
- } else {
- $ok = $memc->set( $locksKey, $locksHeld );
- }
- if ( !$ok ) {
- $status->fatal( 'lockmanager-fail-releaselock', $path );
- }
- } else {
- $status->warning( 'lockmanager-fail-releaselock', $path );
- }
- wfDebug( __METHOD__ . ": released lock on key $locksKey.\n" );
- }
-
- // 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 ) {
- /** @var BagOStuff $memc */
- $memc = null;
- if ( isset( $this->bagOStuffs[$lockSrv] ) ) {
- $memc = $this->bagOStuffs[$lockSrv];
- if ( !isset( $this->serversUp[$lockSrv] ) ) {
- $this->serversUp[$lockSrv] = $memc->set( __CLASS__ . ':ping', 1, 1 );
- if ( !$this->serversUp[$lockSrv] ) {
- trigger_error( __METHOD__ . ": Could not contact $lockSrv.", E_USER_WARNING );
- }
- }
- if ( !$this->serversUp[$lockSrv] ) {
- return null; // server appears to be down
- }
- }
-
- return $memc;
- }
-
- /**
- * @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 static function newLockArray() {
- return [ self::LOCK_SH => [], self::LOCK_EX => [] ];
- }
-
- /**
- * @param array $a
- * @return array An empty lock structure for a key
- */
- protected static function sanitizeLockArray( $a ) {
- if ( is_array( $a ) && isset( $a[self::LOCK_EX] ) && isset( $a[self::LOCK_SH] ) ) {
- return $a;
- } else {
- trigger_error( __METHOD__ . ": reset invalid lock array.", E_USER_WARNING );
-
- return self::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 );
- }
- }
- }
-}