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         // @TODO: change this code to work in one batch
  92         protected function getLocksOnServer( $lockSrv, array $pathsByType ) {
  93                 $status = Status::newGood();
  94
  95                 $lockedPaths = array();
  96                 foreach ( $pathsByType as $type => $paths ) {
  97                         $status->merge( $this->doGetLocksOnServer( $lockSrv, $paths, $type ) );
  98                         if ( $status->isOK() ) {
  99                                 $lockedPaths[$type] = isset( $lockedPaths[$type] )
 100                                         ? array_merge( $lockedPaths[$type], $paths )
 101                                         : $paths;
 102                         } else {
 103                                 foreach ( $lockedPaths as $type => $paths ) {
 104                                         $status->merge( $this->doFreeLocksOnServer( $lockSrv, $paths, $type ) );
 105                                 }
 106                                 break;
 107                         }
 108                 }
 109
 110                 return $status;
 111         }
 112
 113         // @TODO: change this code to work in one batch
 114         protected function freeLocksOnServer( $lockSrv, array $pathsByType ) {
 115                 $status = Status::newGood();
 116
 117                 foreach ( $pathsByType as $type => $paths ) {
 118                         $status->merge( $this->doFreeLocksOnServer( $lockSrv, $paths, $type ) );
 119                 }
 120
 121                 return $status;
 122         }
 123
 124         /**
 125          * @see QuorumLockManager::getLocksOnServer()
 126          * @return Status
 127          */
 128         protected function doGetLocksOnServer( $lockSrv, array $paths, $type ) {
 129                 $status = Status::newGood();
 130
 131                 $memc = $this->getCache( $lockSrv );
 132                 $keys = array_map( array( $this, 'recordKeyForPath' ), $paths ); // lock records
 133
 134                 // Lock all of the active lock record keys...
 135                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
 136                         foreach ( $paths as $path ) {
 137                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 138                         }
 139                         return $status;
 140                 }
 141
 142                 // Fetch all the existing lock records...
 143                 $lockRecords = $memc->getMulti( $keys );
 144
 145                 $now = time();
 146                 // Check if the requested locks conflict with existing ones...
 147                 foreach ( $paths as $path ) {
 148                         $locksKey = $this->recordKeyForPath( $path );
 149                         $locksHeld = isset( $lockRecords[$locksKey] )
 150                                 ? self::sanitizeLockArray( $lockRecords[$locksKey] )
 151                                 : self::newLockArray(); // init
 152                         foreach ( $locksHeld[self::LOCK_EX] as $session => $expiry ) {
 153                                 if ( $expiry < $now ) { // stale?
 154                                         unset( $locksHeld[self::LOCK_EX][$session] );
 155                                 } elseif ( $session !== $this->session ) {
 156                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 157                                 }
 158                         }
 159                         if ( $type === self::LOCK_EX ) {
 160                                 foreach ( $locksHeld[self::LOCK_SH] as $session => $expiry ) {
 161                                         if ( $expiry < $now ) { // stale?
 162                                                 unset( $locksHeld[self::LOCK_SH][$session] );
 163                                         } elseif ( $session !== $this->session ) {
 164                                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 165                                         }
 166                                 }
 167                         }
 168                         if ( $status->isOK() ) {
 169                                 // Register the session in the lock record array
 170                                 $locksHeld[$type][$this->session] = $now + $this->lockTTL;
 171                                 // We will update this record if none of the other locks conflict
 172                                 $lockRecords[$locksKey] = $locksHeld;
 173                         }
 174                 }
 175
 176                 // If there were no lock conflicts, update all the lock records...
 177                 if ( $status->isOK() ) {
 178                         foreach ( $paths as $path ) {
 179                                 $locksKey = $this->recordKeyForPath( $path );
 180                                 $locksHeld = $lockRecords[$locksKey];
 181                                 $ok = $memc->set( $locksKey, $locksHeld, 7 * 86400 );
 182                                 if ( !$ok ) {
 183                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 184                                 } else {
 185                                         wfDebug( __METHOD__ . ": acquired lock on key $locksKey.\n" );
 186                                 }
 187                         }
 188                 }
 189
 190                 // Unlock all of the active lock record keys...
 191                 $this->releaseMutexes( $memc, $keys );
 192
 193                 return $status;
 194         }
 195
 196         /**
 197          * @see QuorumLockManager::freeLocksOnServer()
 198          * @return Status
 199          */
 200         protected function doFreeLocksOnServer( $lockSrv, array $paths, $type ) {
 201                 $status = Status::newGood();
 202
 203                 $memc = $this->getCache( $lockSrv );
 204                 $keys = array_map( array( $this, 'recordKeyForPath' ), $paths ); // lock records
 205
 206                 // Lock all of the active lock record keys...
 207                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
 208                         foreach ( $paths as $path ) {
 209                                 $status->fatal( 'lockmanager-fail-releaselock', $path );
 210                         }
 211                         return;
 212                 }
 213
 214                 // Fetch all the existing lock records...
 215                 $lockRecords = $memc->getMulti( $keys );
 216
 217                 // Remove the requested locks from all records...
 218                 foreach ( $paths as $path ) {
 219                         $locksKey = $this->recordKeyForPath( $path ); // lock record
 220                         if ( !isset( $lockRecords[$locksKey] ) ) {
 221                                 $status->warning( 'lockmanager-fail-releaselock', $path );
 222                                 continue; // nothing to do
 223                         }
 224                         $locksHeld = self::sanitizeLockArray( $lockRecords[$locksKey] );
 225                         if ( isset( $locksHeld[$type][$this->session] ) ) {
 226                                 unset( $locksHeld[$type][$this->session] ); // unregister this session
 227                                 if ( $locksHeld === self::newLockArray() ) {
 228                                         $ok = $memc->delete( $locksKey );
 229                                 } else {
 230                                         $ok = $memc->set( $locksKey, $locksHeld );
 231                                 }
 232                                 if ( !$ok ) {
 233                                         $status->fatal( 'lockmanager-fail-releaselock', $path );
 234                                 }
 235                         } else {
 236                                 $status->warning( 'lockmanager-fail-releaselock', $path );
 237                         }
 238                         wfDebug( __METHOD__ . ": released lock on key $locksKey.\n" );
 239                 }
 240
 241                 // Unlock all of the active lock record keys...
 242                 $this->releaseMutexes( $memc, $keys );
 243
 244                 return $status;
 245         }
 246
 247         /**
 248          * @see QuorumLockManager::releaseAllLocks()
 249          * @return Status
 250          */
 251         protected function releaseAllLocks() {
 252                 return Status::newGood(); // not supported
 253         }
 254
 255         /**
 256          * @see QuorumLockManager::isServerUp()
 257          * @return bool
 258          */
 259         protected function isServerUp( $lockSrv ) {
 260                 return (bool)$this->getCache( $lockSrv );
 261         }
 262
 263         /**
 264          * Get the MemcachedBagOStuff object for a $lockSrv
 265          *
 266          * @param string $lockSrv Server name
 267          * @return MemcachedBagOStuff|null
 268          */
 269         protected function getCache( $lockSrv ) {
 270                 $memc = null;
 271                 if ( isset( $this->bagOStuffs[$lockSrv] ) ) {
 272                         $memc = $this->bagOStuffs[$lockSrv];
 273                         if ( !isset( $this->serversUp[$lockSrv] ) ) {
 274                                 $this->serversUp[$lockSrv] = $memc->set( __CLASS__ . ':ping', 1, 1 );
 275                                 if ( !$this->serversUp[$lockSrv] ) {
 276                                         trigger_error( __METHOD__ . ": Could not contact $lockSrv.", E_USER_WARNING );
 277                                 }
 278                         }
 279                         if ( !$this->serversUp[$lockSrv] ) {
 280                                 return null; // server appears to be down
 281                         }
 282                 }
 283                 return $memc;
 284         }
 285
 286         /**
 287          * @param $path string
 288          * @return string
 289          */
 290         protected function recordKeyForPath( $path ) {
 291                 return implode( ':', array( __CLASS__, 'locks', $this->sha1Base36Absolute( $path ) ) );
 292         }
 293
 294         /**
 295          * @return Array An empty lock structure for a key
 296          */
 297         protected static function newLockArray() {
 298                 return array( self::LOCK_SH => array(), self::LOCK_EX => array() );
 299         }
 300
 301         /**
 302          * @param $a array
 303          * @return Array An empty lock structure for a key
 304          */
 305         protected static function sanitizeLockArray( $a ) {
 306                 if ( is_array( $a ) && isset( $a[self::LOCK_EX] ) && isset( $a[self::LOCK_SH] ) ) {
 307                         return $a;
 308                 } else {
 309                         trigger_error( __METHOD__ . ": reset invalid lock array.", E_USER_WARNING );
 310                         return self::newLockArray();
 311                 }
 312         }
 313
 314         /**
 315          * @param $memc MemcachedBagOStuff
 316          * @param array $keys List of keys to acquire
 317          * @return bool
 318          */
 319         protected function acquireMutexes( MemcachedBagOStuff $memc, array $keys ) {
 320                 $lockedKeys = array();
 321
 322                 // Acquire the keys in lexicographical order, to avoid deadlock problems.
 323                 // If P1 is waiting to acquire a key P2 has, P2 can't also be waiting for a key P1 has.
 324                 sort( $keys );
 325
 326                 // Try to quickly loop to acquire the keys, but back off after a few rounds.
 327                 // This reduces memcached spam, especially in the rare case where a server acquires
 328                 // some lock keys and dies without releasing them. Lock keys expire after a few minutes.
 329                 $rounds = 0;
 330                 $start = microtime( true );
 331                 do {
 332                         if ( ( ++$rounds % 4 ) == 0 ) {
 333                                 usleep( 1000 * 50 ); // 50 ms
 334                         }
 335                         foreach ( array_diff( $keys, $lockedKeys ) as $key ) {
 336                                 if ( $memc->add( "$key:mutex", 1, 180 ) ) { // lock record
 337                                         $lockedKeys[] = $key;
 338                                 } else {
 339                                         continue; // acquire in order
 340                                 }
 341                         }
 342                 } while ( count( $lockedKeys ) < count( $keys ) && ( microtime( true ) - $start ) <= 3 );
 343
 344                 if ( count( $lockedKeys ) != count( $keys ) ) {
 345                         $this->releaseMutexes( $memc, $lockedKeys ); // failed; release what was locked
 346                         return false;
 347                 }
 348
 349                 return true;
 350         }
 351
 352         /**
 353          * @param $memc MemcachedBagOStuff
 354          * @param array $keys List of acquired keys
 355          * @return void
 356          */
 357         protected function releaseMutexes( MemcachedBagOStuff $memc, array $keys ) {
 358                 foreach ( $keys as $key ) {
 359                         $memc->delete( "$key:mutex" );
 360                 }
 361         }
 362
 363         /**
 364          * Make sure remaining locks get cleared for sanity
 365          */
 366         function __destruct() {
 367                 while ( count( $this->locksHeld ) ) {
 368                         foreach ( $this->locksHeld as $path => $locks ) {
 369                                 $this->doUnlock( array( $path ), self::LOCK_EX );
 370                                 $this->doUnlock( array( $path ), self::LOCK_SH );
 371                         }
 372                 }
 373         }
 374 }