Current File : /www/varak.net/wiki.varak.net/includes/filebackend/lockmanager/MemcLockManager.php
<?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 );
}
}
}
}
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