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 to one
  32  * 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 $session = ''; // string; random UUID
  52
  53         /**
  54          * Construct a new instance from configuration.
  55          *
  56          * $config paramaters include:
  57          *   - lockServers  : Associative array of server names to "<IP>:<port>" strings.
  58          *   - srvsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
  59          *                    each having an odd-numbered list of server names (peers) as values.
  60          *   - memcConfig   : Configuration array for ObjectCache::newFromParams. [optional]
  61          *                    If set, this must use one of the memcached classes.
  62          *
  63          * @param array $config
  64          * @throws MWException
  65          */
  66         public function __construct( array $config ) {
  67                 parent::__construct( $config );
  68
  69                 // Sanitize srvsByBucket config to prevent PHP errors
  70                 $this->srvsByBucket = array_filter( $config['srvsByBucket'], 'is_array' );
  71                 $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
  72
  73                 $memcConfig = isset( $config['memcConfig'] )
  74                         ? $config['memcConfig']
  75                         : array( 'class' => 'MemcachedPhpBagOStuff' );
  76
  77                 foreach ( $config['lockServers'] as $name => $address ) {
  78                         $params = array( 'servers' => array( $address ) ) + $memcConfig;
  79                         $cache = ObjectCache::newFromParams( $params );
  80                         if ( $cache instanceof MemcachedBagOStuff ) {
  81                                 $this->bagOStuffs[$name] = $cache;
  82                         } else {
  83                                 throw new MWException(
  84                                         'Only MemcachedBagOStuff classes are supported by MemcLockManager.' );
  85                         }
  86                 }
  87
  88                 $this->session = wfRandomString( 32 );
  89         }
  90
  91         /**
  92          * @see QuorumLockManager::getLocksOnServer()
  93          * @return Status
  94          */
  95         protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
  96                 $status = Status::newGood();
  97
  98                 $memc = $this->getCache( $lockSrv );
  99                 $keys = array_map( array( $this, 'recordKeyForPath' ), $paths ); // lock records
 100
 101                 // Lock all of the active lock record keys...
 102                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
 103                         foreach ( $paths as $path ) {
 104                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 105                         }
 106                         return $status;
 107                 }
 108
 109                 // Fetch all the existing lock records...
 110                 $lockRecords = $memc->getMulti( $keys );
 111
 112                 $now = time();
 113                 // Check if the requested locks conflict with existing ones...
 114                 foreach ( $paths as $path ) {
 115                         $locksKey = $this->recordKeyForPath( $path );
 116                         $locksHeld = isset( $lockRecords[$locksKey] )
 117                                 ? self::sanitizeLockArray( $lockRecords[$locksKey] )
 118                                 : self::newLockArray(); // init
 119                         foreach ( $locksHeld[self::LOCK_EX] as $session => $expiry ) {
 120                                 if ( $expiry < $now ) { // stale?
 121                                         unset( $locksHeld[self::LOCK_EX][$session] );
 122                                 } elseif ( $session !== $this->session ) {
 123                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 124                                 }
 125                         }
 126                         if ( $type === self::LOCK_EX ) {
 127                                 foreach ( $locksHeld[self::LOCK_SH] as $session => $expiry ) {
 128                                         if ( $expiry < $now ) { // stale?
 129                                                 unset( $locksHeld[self::LOCK_SH][$session] );
 130                                         } elseif ( $session !== $this->session ) {
 131                                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 132                                         }
 133                                 }
 134                         }
 135                         if ( $status->isOK() ) {
 136                                 // Register the session in the lock record array
 137                                 $locksHeld[$type][$this->session] = $now + $this->lockTTL;
 138                                 // We will update this record if none of the other locks conflict
 139                                 $lockRecords[$locksKey] = $locksHeld;
 140                         }
 141                 }
 142
 143                 // If there were no lock conflicts, update all the lock records...
 144                 if ( $status->isOK() ) {
 145                         foreach ( $paths as $path ) {
 146                                 $locksKey = $this->recordKeyForPath( $path );
 147                                 $locksHeld = $lockRecords[$locksKey];
 148                                 $ok = $memc->set( $locksKey, $locksHeld, 7 * 86400 );
 149                                 if ( !$ok ) {
 150                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 151                                 } else {
 152                                         wfDebug( __METHOD__ . ": acquired lock on key $locksKey.\n" );
 153                                 }
 154                         }
 155                 }
 156
 157                 // Unlock all of the active lock record keys...
 158                 $this->releaseMutexes( $memc, $keys );
 159
 160                 return $status;
 161         }
 162
 163         /**
 164          * @see QuorumLockManager::freeLocksOnServer()
 165          * @return Status
 166          */
 167         protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
 168                 $status = Status::newGood();
 169
 170                 $memc = $this->getCache( $lockSrv );
 171                 $keys = array_map( array( $this, 'recordKeyForPath' ), $paths ); // lock records
 172
 173                 // Lock all of the active lock record keys...
 174                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
 175                         foreach ( $paths as $path ) {
 176                                 $status->fatal( 'lockmanager-fail-releaselock', $path );
 177                         }
 178                         return;
 179                 }
 180
 181                 // Fetch all the existing lock records...
 182                 $lockRecords = $memc->getMulti( $keys );
 183
 184                 // Remove the requested locks from all records...
 185                 foreach ( $paths as $path ) {
 186                         $locksKey = $this->recordKeyForPath( $path ); // lock record
 187                         if ( !isset( $lockRecords[$locksKey] ) ) {
 188                                 $status->warning( 'lockmanager-fail-releaselock', $path );
 189                                 continue; // nothing to do
 190                         }
 191                         $locksHeld = self::sanitizeLockArray( $lockRecords[$locksKey] );
 192                         if ( isset( $locksHeld[$type][$this->session] ) ) {
 193                                 unset( $locksHeld[$type][$this->session] ); // unregister this session
 194                                 if ( $locksHeld === self::newLockArray() ) {
 195                                         $ok = $memc->delete( $locksKey );
 196                                 } else {
 197                                         $ok = $memc->set( $locksKey, $locksHeld );
 198                                 }
 199                                 if ( !$ok ) {
 200                                         $status->fatal( 'lockmanager-fail-releaselock', $path );
 201                                 }
 202                         } else {
 203                                 $status->warning( 'lockmanager-fail-releaselock', $path );
 204                         }
 205                         wfDebug( __METHOD__ . ": released lock on key $locksKey.\n" );
 206                 }
 207
 208                 // Unlock all of the active lock record keys...
 209                 $this->releaseMutexes( $memc, $keys );
 210
 211                 return $status;
 212         }
 213
 214         /**
 215          * @see QuorumLockManager::releaseAllLocks()
 216          * @return Status
 217          */
 218         protected function releaseAllLocks() {
 219                 return Status::newGood(); // not supported
 220         }
 221
 222         /**
 223          * @see QuorumLockManager::isServerUp()
 224          * @return bool
 225          */
 226         protected function isServerUp( $lockSrv ) {
 227                 return (bool)$this->getCache( $lockSrv );
 228         }
 229
 230         /**
 231          * Get the MemcachedBagOStuff object for a $lockSrv
 232          *
 233          * @param string $lockSrv Server name
 234          * @return MemcachedBagOStuff|null
 235          */
 236         protected function getCache( $lockSrv ) {
 237                 $memc = null;
 238                 if ( isset( $this->bagOStuffs[$lockSrv] ) ) {
 239                         $memc = $this->bagOStuffs[$lockSrv];
 240                         if ( !isset( $this->serversUp[$lockSrv] ) ) {
 241                                 $this->serversUp[$lockSrv] = $memc->set( __CLASS__ . ':ping', 1, 1 );
 242                                 if ( !$this->serversUp[$lockSrv] ) {
 243                                         trigger_error( __METHOD__ . ": Could not contact $lockSrv.", E_USER_WARNING );
 244                                 }
 245                         }
 246                         if ( !$this->serversUp[$lockSrv] ) {
 247                                 return null; // server appears to be down
 248                         }
 249                 }
 250                 return $memc;
 251         }
 252
 253         /**
 254          * @param $path string
 255          * @return string
 256          */
 257         protected function recordKeyForPath( $path ) {
 258                 return implode( ':', array( __CLASS__, 'locks', $this->sha1Base36Absolute( $path ) ) );
 259         }
 260
 261         /**
 262          * @return Array An empty lock structure for a key
 263          */
 264         protected static function newLockArray() {
 265                 return array( self::LOCK_SH => array(), self::LOCK_EX => array() );
 266         }
 267
 268         /**
 269          * @param $a array
 270          * @return Array An empty lock structure for a key
 271          */
 272         protected static function sanitizeLockArray( $a ) {
 273                 if ( is_array( $a ) && isset( $a[self::LOCK_EX] ) && isset( $a[self::LOCK_SH] ) ) {
 274                         return $a;
 275                 } else {
 276                         trigger_error( __METHOD__ . ": reset invalid lock array.", E_USER_WARNING );
 277                         return self::newLockArray();
 278                 }
 279         }
 280
 281         /**
 282          * @param $memc MemcachedBagOStuff
 283          * @param array $keys List of keys to acquire
 284          * @return bool
 285          */
 286         protected function acquireMutexes( MemcachedBagOStuff $memc, array $keys ) {
 287                 $lockedKeys = array();
 288
 289                 // Acquire the keys in lexicographical order, to avoid deadlock problems.
 290                 // If P1 is waiting to acquire a key P2 has, P2 can't also be waiting for a key P1 has.
 291                 sort( $keys );
 292
 293                 // Try to quickly loop to acquire the keys, but back off after a few rounds.
 294                 // This reduces memcached spam, especially in the rare case where a server acquires
 295                 // some lock keys and dies without releasing them. Lock keys expire after a few minutes.
 296                 $rounds = 0;
 297                 $start = microtime( true );
 298                 do {
 299                         if ( ( ++$rounds % 4 ) == 0 ) {
 300                                 usleep( 1000 * 50 ); // 50 ms
 301                         }
 302                         foreach ( array_diff( $keys, $lockedKeys ) as $key ) {
 303                                 if ( $memc->add( "$key:mutex", 1, 180 ) ) { // lock record
 304                                         $lockedKeys[] = $key;
 305                                 } else {
 306                                         continue; // acquire in order
 307                                 }
 308                         }
 309                 } while ( count( $lockedKeys ) < count( $keys ) && ( microtime( true ) - $start ) <= 3 );
 310
 311                 if ( count( $lockedKeys ) != count( $keys ) ) {
 312                         $this->releaseMutexes( $memc, $lockedKeys ); // failed; release what was locked
 313                         return false;
 314                 }
 315
 316                 return true;
 317         }
 318
 319         /**
 320          * @param $memc MemcachedBagOStuff
 321          * @param array $keys List of acquired keys
 322          * @return void
 323          */
 324         protected function releaseMutexes( MemcachedBagOStuff $memc, array $keys ) {
 325                 foreach ( $keys as $key ) {
 326                         $memc->delete( "$key:mutex" );
 327                 }
 328         }
 329
 330         /**
 331          * Make sure remaining locks get cleared for sanity
 332          */
 333         function __destruct() {
 334                 while ( count( $this->locksHeld ) ) {
 335                         foreach ( $this->locksHeld as $path => $locks ) {
 336                                 $this->doUnlock( array( $path ), self::LOCK_EX );
 337                                 $this->doUnlock( array( $path ), self::LOCK_SH );
 338                         }
 339                 }
 340         }
 341 }