includes/filebackend/lockmanager/MemcLockManager.php

   1 <?php
   2 /**
   3  * Version of LockManager based on using memcached servers.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup LockManager
  22  */
  23
  24 /**
  25  * Manage locks using memcached servers.
  26  *
  27  * Version of LockManager based on using memcached servers.
  28  * This is meant for multi-wiki systems that may share files.
  29  * All locks are non-blocking, which avoids deadlocks.
  30  *
  31  * All lock requests for a resource, identified by a hash string, will map
  32  * to one bucket. Each bucket maps to one or several peer servers, each running memcached.
  33  * A majority of peers must agree for a lock to be acquired.
  34  *
  35  * @ingroup LockManager
  36  * @since 1.20
  37  */
  38 class MemcLockManager extends QuorumLockManager {
  39         /** @var Array Mapping of lock types to the type actually used */
  40         protected $lockTypeMap = array(
  41                 self::LOCK_SH => self::LOCK_SH,
  42                 self::LOCK_UW => self::LOCK_SH,
  43                 self::LOCK_EX => self::LOCK_EX
  44         );
  45
  46         /** @var Array Map server names to MemcachedBagOStuff objects */
  47         protected $bagOStuffs = array();
  48         /** @var Array */
  49         protected $serversUp = array(); // (server name => bool)
  50
  51         protected $lockExpiry; // integer; maximum time locks can be held
  52         protected $session = ''; // string; random SHA-1 UUID
  53
  54         /**
  55          * Construct a new instance from configuration.
  56          *
  57          * $config paramaters include:
  58          *   - lockServers  : Associative array of server names to "<IP>:<port>" strings.
  59          *   - srvsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
  60          *                    each having an odd-numbered list of server names (peers) as values.
  61          *   - memcConfig   : Configuration array for ObjectCache::newFromParams. [optional]
  62          *                    If set, this must use one of the memcached classes.
  63          *
  64          * @param array $config
  65          * @throws MWException
  66          */
  67         public function __construct( array $config ) {
  68                 parent::__construct( $config );
  69
  70                 // Sanitize srvsByBucket config to prevent PHP errors
  71                 $this->srvsByBucket = array_filter( $config['srvsByBucket'], 'is_array' );
  72                 $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
  73
  74                 $memcConfig = isset( $config['memcConfig'] )
  75                         ? $config['memcConfig']
  76                         : array( 'class' => 'MemcachedPhpBagOStuff' );
  77
  78                 foreach ( $config['lockServers'] as $name => $address ) {
  79                         $params = array( 'servers' => array( $address ) ) + $memcConfig;
  80                         $cache = ObjectCache::newFromParams( $params );
  81                         if ( $cache instanceof MemcachedBagOStuff ) {
  82                                 $this->bagOStuffs[$name] = $cache;
  83                         } else {
  84                                 throw new MWException(
  85                                         'Only MemcachedBagOStuff classes are supported by MemcLockManager.' );
  86                         }
  87                 }
  88
  89                 $met = ini_get( 'max_execution_time' ); // this is 0 in CLI mode
  90                 $this->lockExpiry = $met ? 2*(int)$met : 2*3600;
  91
  92                 $this->session = wfRandomString( 32 );
  93         }
  94
  95         /**
  96          * @see QuorumLockManager::getLocksOnServer()
  97          * @return Status
  98          */
  99         protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
 100                 $status = Status::newGood();
 101
 102                 $memc = $this->getCache( $lockSrv );
 103                 $keys = array_map( array( $this, 'recordKeyForPath' ), $paths ); // lock records
 104
 105                 // Lock all of the active lock record keys...
 106                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
 107                         foreach ( $paths as $path ) {
 108                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 109                         }
 110                         return $status;
 111                 }
 112
 113                 // Fetch all the existing lock records...
 114                 $lockRecords = $memc->getMulti( $keys );
 115
 116                 $now = time();
 117                 // Check if the requested locks conflict with existing ones...
 118                 foreach ( $paths as $path ) {
 119                         $locksKey = $this->recordKeyForPath( $path );
 120                         $locksHeld = isset( $lockRecords[$locksKey] )
 121                                 ? $lockRecords[$locksKey]
 122                                 : array( self::LOCK_SH => array(), self::LOCK_EX => array() ); // init
 123                         foreach ( $locksHeld[self::LOCK_EX] as $session => $expiry ) {
 124                                 if ( $expiry < $now ) { // stale?
 125                                         unset( $locksHeld[self::LOCK_EX][$session] );
 126                                 } elseif ( $session !== $this->session ) {
 127                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 128                                 }
 129                         }
 130                         if ( $type === self::LOCK_EX ) {
 131                                 foreach ( $locksHeld[self::LOCK_SH] as $session => $expiry ) {
 132                                         if ( $expiry < $now ) { // stale?
 133                                                 unset( $locksHeld[self::LOCK_SH][$session] );
 134                                         } elseif ( $session !== $this->session ) {
 135                                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 136                                         }
 137                                 }
 138                         }
 139                         if ( $status->isOK() ) {
 140                                 // Register the session in the lock record array
 141                                 $locksHeld[$type][$this->session] = $now + $this->lockExpiry;
 142                                 // We will update this record if none of the other locks conflict
 143                                 $lockRecords[$locksKey] = $locksHeld;
 144                         }
 145                 }
 146
 147                 // If there were no lock conflicts, update all the lock records...
 148                 if ( $status->isOK() ) {
 149                         foreach ( $lockRecords as $locksKey => $locksHeld ) {
 150                                 $memc->set( $locksKey, $locksHeld );
 151                                 wfDebug( __METHOD__ . ": acquired lock on key $locksKey.\n" );
 152                         }
 153                 }
 154
 155                 // Unlock all of the active lock record keys...
 156                 $this->releaseMutexes( $memc, $keys );
 157
 158                 return $status;
 159         }
 160
 161         /**
 162          * @see QuorumLockManager::freeLocksOnServer()
 163          * @return Status
 164          */
 165         protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
 166                 $status = Status::newGood();
 167
 168                 $memc = $this->getCache( $lockSrv );
 169                 $keys = array_map( array( $this, 'recordKeyForPath' ), $paths ); // lock records
 170
 171                 // Lock all of the active lock record keys...
 172                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
 173                         foreach ( $paths as $path ) {
 174                                 $status->fatal( 'lockmanager-fail-releaselock', $path );
 175                         }
 176                         return;
 177                 }
 178
 179                 // Fetch all the existing lock records...
 180                 $lockRecords = $memc->getMulti( $keys );
 181
 182                 // Remove the requested locks from all records...
 183                 foreach ( $paths as $path ) {
 184                         $locksKey = $this->recordKeyForPath( $path ); // lock record
 185                         if ( !isset( $lockRecords[$locksKey] ) ) {
 186                                 continue; // nothing to do
 187                         }
 188                         $locksHeld = $lockRecords[$locksKey];
 189                         if ( is_array( $locksHeld ) && isset( $locksHeld[$type] ) ) {
 190                                 unset( $locksHeld[$type][$this->session] );
 191                                 $ok = $memc->set( $locksKey, $locksHeld );
 192                         } else {
 193                                 $ok = true;
 194                         }
 195                         if ( !$ok ) {
 196                                 $status->fatal( 'lockmanager-fail-releaselock', $path );
 197                         }
 198                         wfDebug( __METHOD__ . ": released lock on key $locksKey.\n" );
 199                 }
 200
 201                 // Unlock all of the active lock record keys...
 202                 $this->releaseMutexes( $memc, $keys );
 203
 204                 return $status;
 205         }
 206
 207         /**
 208          * @see QuorumLockManager::releaseAllLocks()
 209          * @return Status
 210          */
 211         protected function releaseAllLocks() {
 212                 return Status::newGood(); // not supported
 213         }
 214
 215         /**
 216          * @see QuorumLockManager::isServerUp()
 217          * @return bool
 218          */
 219         protected function isServerUp( $lockSrv ) {
 220                 return (bool)$this->getCache( $lockSrv );
 221         }
 222
 223         /**
 224          * Get the MemcachedBagOStuff object for a $lockSrv
 225          *
 226          * @param string $lockSrv Server name
 227          * @return MemcachedBagOStuff|null
 228          */
 229         protected function getCache( $lockSrv ) {
 230                 $memc = null;
 231                 if ( isset( $this->bagOStuffs[$lockSrv] ) ) {
 232                         $memc = $this->bagOStuffs[$lockSrv];
 233                         if ( !isset( $this->serversUp[$lockSrv] ) ) {
 234                                 $this->serversUp[$lockSrv] = $memc->set( 'MemcLockManager:ping', 1, 1 );
 235                                 if ( !$this->serversUp[$lockSrv] ) {
 236                                         trigger_error( __METHOD__ . ": Could not contact $lockSrv.", E_USER_WARNING );
 237                                 }
 238                         }
 239                         if ( !$this->serversUp[$lockSrv] ) {
 240                                 return null; // server appears to be down
 241                         }
 242                 }
 243                 return $memc;
 244         }
 245
 246         /**
 247          * @param $path string
 248          * @return string
 249          */
 250         protected function recordKeyForPath( $path ) {
 251                 return implode( ':', array( __CLASS__, 'locks', $this->sha1Base36Absolute( $path ) ) );
 252         }
 253
 254         /**
 255          * @param $memc MemcachedBagOStuff
 256          * @param array $keys List of keys to acquire
 257          * @return bool
 258          */
 259         protected function acquireMutexes( MemcachedBagOStuff $memc, array $keys ) {
 260                 $lockedKeys = array();
 261
 262                 // Acquire the keys in lexicographical order, to avoid deadlock problems.
 263                 // If P1 is waiting to acquire a key P2 has, P2 can't also be waiting for a key P1 has.
 264                 sort( $keys );
 265
 266                 // Try to quickly loop to acquire the keys, but back off after a few rounds.
 267                 // This reduces memcached spam, especially in the rare case where a server acquires
 268                 // some lock keys and dies without releasing them. Lock keys expire after a few minutes.
 269                 $rounds = 0;
 270                 $start = microtime( true );
 271                 do {
 272                         if ( ( ++$rounds % 4 ) == 0 ) {
 273                                 usleep( 1000*50 ); // 50 ms
 274                         }
 275                         foreach ( array_diff( $keys, $lockedKeys ) as $key ) {
 276                                 if ( $memc->add( "$key:mutex", 1, 180 ) ) { // lock record
 277                                         $lockedKeys[] = $key;
 278                                 } else {
 279                                         continue; // acquire in order
 280                                 }
 281                         }
 282                 } while ( count( $lockedKeys ) < count( $keys ) && ( microtime( true ) - $start ) <= 6 );
 283
 284                 if ( count( $lockedKeys ) != count( $keys ) ) {
 285                         $this->releaseMutexes( $lockedKeys ); // failed; release what was locked
 286                         return false;
 287                 }
 288
 289                 return true;
 290         }
 291
 292         /**
 293          * @param $memc MemcachedBagOStuff
 294          * @param array $keys List of acquired keys
 295          * @return void
 296          */
 297         protected function releaseMutexes( MemcachedBagOStuff $memc, array $keys ) {
 298                 foreach ( $keys as $key ) {
 299                         $memc->delete( "$key:mutex" );
 300                 }
 301         }
 302
 303         /**
 304          * Make sure remaining locks get cleared for sanity
 305          */
 306         function __destruct() {
 307                 while ( count( $this->locksHeld ) ) {
 308                         foreach ( $this->locksHeld as $path => $locks ) {
 309                                 $this->doUnlock( array( $path ), self::LOCK_EX );
 310                                 $this->doUnlock( array( $path ), self::LOCK_SH );
 311                         }
 312                 }
 313         }
 314 }