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MemcLockManager.php
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MemcLockManager.php
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<?php
/**
* 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
*/
use Wikimedia\ObjectCache\MemcachedBagOStuff;
use Wikimedia\ObjectCache\MemcachedPhpBagOStuff;
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 MapCacheLRU 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 : An array of up to 16 arrays, each containing the server names
* in a bucket. Each bucket should have an odd number of servers.
* If omitted, all servers will be in one bucket. [optional].
* - 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 );
if ( isset( $config['srvsByBucket'] ) ) {
// Sanitize srvsByBucket config to prevent PHP errors
$this->srvsByBucket = array_filter( $config['srvsByBucket'], 'is_array' );
$this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
} else {
$this->srvsByBucket = [ array_keys( $config['lockServers'] ) ];
}
$memcConfig = $config['memcConfig'] ?? [];
$memcConfig += [ 'class' => MemcachedPhpBagOStuff::class ]; // default
$class = $memcConfig['class'];
if ( !is_subclass_of( $class, MemcachedBagOStuff::class ) ) {
throw new InvalidArgumentException( "$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 MapCacheLRU( 100 );
}
protected function getLocksOnServer( $lockSrv, array $pathsByType ) {
$status = StatusValue::newGood();
$memc = $this->getCache( $lockSrv );
// List of affected paths
$paths = 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 ) ) {
$status->fatal( 'lockmanager-fail-conflict' );
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 => $paths2 ) {
foreach ( $paths2 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-conflict' );
}
}
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-conflict' );
}
}
}
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." );
}
}
}
// 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 = 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 => $paths2 ) {
foreach ( $paths2 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." );
} 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", 30 );
if ( $online === null ) {
$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 );
}
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(
static 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
*/
public function __destruct() {
$pathsByType = [];
foreach ( $this->locksHeld as $path => $locks ) {
foreach ( $locks as $type => $count ) {
$pathsByType[$type][] = $path;
}
}
if ( $pathsByType ) {
$this->unlockByType( $pathsByType );
}
}
}

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Expires
Wed, Aug 19, 02:46 (2 w, 2 d ago)
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c6/57/d37f58a3ae5937d085f8d40ea557
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MemcLockManager.php (11 KB)

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