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         protected $wikiId = ''; // string
  54
  55         /**
  56          * Construct a new instance from configuration.
  57          *
  58          * $config paramaters include:
  59          *   - lockServers  : Associative array of server names to "<IP>:<port>" strings.
  60          *   - srvsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
  61          *                    each having an odd-numbered list of server names (peers) as values.
  62          *   - memcConfig   : Configuration array for ObjectCache::newFromParams. [optional]
  63          *                    If set, this must use one of the memcached classes.
  64          *   - wikiId       : Wiki ID string that all resources are relative to. [optional]
  65          *
  66          * @param Array $config
  67          * @throws MWException
  68          */
  69         public function __construct( array $config ) {
  70                 parent::__construct( $config );
  71
  72                 // Sanitize srvsByBucket config to prevent PHP errors
  73                 $this->srvsByBucket = array_filter( $config['srvsByBucket'], 'is_array' );
  74                 $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
  75
  76                 $memcConfig = isset( $config['memcConfig'] )
  77                         ? $config['memcConfig']
  78                         : array( 'class' => 'MemcachedPhpBagOStuff' );
  79
  80                 foreach ( $config['lockServers'] as $name => $address ) {
  81                         $params = array( 'servers' => array( $address ) ) + $memcConfig;
  82                         $cache = ObjectCache::newFromParams( $params );
  83                         if ( $cache instanceof MemcachedBagOStuff ) {
  84                                 $this->bagOStuffs[$name] = $cache;
  85                         } else {
  86                                 throw new MWException(
  87                                         'Only MemcachedBagOStuff classes are supported by MemcLockManager.' );
  88                         }
  89                 }
  90
  91                 $this->wikiId = isset( $config['wikiId'] ) ? $config['wikiId'] : wfWikiID();
  92
  93                 $met = ini_get( 'max_execution_time' ); // this is 0 in CLI mode
  94                 $this->lockExpiry = $met ? 2*(int)$met : 2*3600;
  95
  96                 $this->session = wfRandomString( 32 );
  97         }
  98
  99         /**
 100          * @see QuorumLockManager::getLocksOnServer()
 101          * @return Status
 102          */
 103         protected function getLocksOnServer( $lockSrv, array $paths, $type ) {
 104                 $status = Status::newGood();
 105
 106                 $memc = $this->getCache( $lockSrv );
 107                 $keys = array_map( array( $this, 'recordKeyForPath' ), $paths ); // lock records
 108
 109                 // Lock all of the active lock record keys...
 110                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
 111                         foreach ( $paths as $path ) {
 112                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 113                         }
 114                         return;
 115                 }
 116
 117                 // Fetch all the existing lock records...
 118                 $lockRecords = $memc->getMulti( $keys );
 119
 120                 $now = time();
 121                 // Check if the requested locks conflict with existing ones...
 122                 foreach ( $paths as $path ) {
 123                         $locksKey = $this->recordKeyForPath( $path );
 124                         $locksHeld = isset( $lockRecords[$locksKey] )
 125                                 ? $lockRecords[$locksKey]
 126                                 : array( self::LOCK_SH => array(), self::LOCK_EX => array() ); // init
 127                         foreach ( $locksHeld[self::LOCK_EX] as $session => $expiry ) {
 128                                 if ( $expiry < $now ) { // stale?
 129                                         unset( $locksHeld[self::LOCK_EX][$session] );
 130                                 } elseif ( $session !== $this->session ) {
 131                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 132                                 }
 133                         }
 134                         if ( $type === self::LOCK_EX ) {
 135                                 foreach ( $locksHeld[self::LOCK_SH] as $session => $expiry ) {
 136                                         if ( $expiry < $now ) { // stale?
 137                                                 unset( $locksHeld[self::LOCK_SH][$session] );
 138                                         } elseif ( $session !== $this->session ) {
 139                                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 140                                         }
 141                                 }
 142                         }
 143                         if ( $status->isOK() ) {
 144                                 // Register the session in the lock record array
 145                                 $locksHeld[$type][$this->session] = $now + $this->lockExpiry;
 146                                 // We will update this record if none of the other locks conflict
 147                                 $lockRecords[$locksKey] = $locksHeld;
 148                         }
 149                 }
 150
 151                 // If there were no lock conflicts, update all the lock records...
 152                 if ( $status->isOK() ) {
 153                         foreach ( $lockRecords as $locksKey => $locksHeld ) {
 154                                 $memc->set( $locksKey, $locksHeld );
 155                                 wfDebug( __METHOD__ . ": acquired lock on key $locksKey.\n" );
 156                         }
 157                 }
 158
 159                 // Unlock all of the active lock record keys...
 160                 $this->releaseMutexes( $memc, $keys );
 161
 162                 return $status;
 163         }
 164
 165         /**
 166          * @see QuorumLockManager::freeLocksOnServer()
 167          * @return Status
 168          */
 169         protected function freeLocksOnServer( $lockSrv, array $paths, $type ) {
 170                 $status = Status::newGood();
 171
 172                 $memc = $this->getCache( $lockSrv );
 173                 $keys = array_map( array( $this, 'recordKeyForPath' ), $paths ); // lock records
 174
 175                 // Lock all of the active lock record keys...
 176                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
 177                         foreach ( $paths as $path ) {
 178                                 $status->fatal( 'lockmanager-fail-releaselock', $path );
 179                         }
 180                         return;
 181                 }
 182
 183                 // Fetch all the existing lock records...
 184                 $lockRecords = $memc->getMulti( $keys );
 185
 186                 // Remove the requested locks from all records...
 187                 foreach ( $paths as $path ) {
 188                         $locksKey = $this->recordKeyForPath( $path ); // lock record
 189                         if ( !isset( $lockRecords[$locksKey] ) ) {
 190                                 continue; // nothing to do
 191                         }
 192                         $locksHeld = $lockRecords[$locksKey];
 193                         if ( is_array( $locksHeld ) && isset( $locksHeld[$type] ) ) {
 194                                 unset( $locksHeld[$type][$this->session] );
 195                                 $ok = $memc->set( $locksKey, $locksHeld );
 196                         } else {
 197                                 $ok = true;
 198                         }
 199                         if ( !$ok ) {
 200                                 $status->fatal( 'lockmanager-fail-releaselock', $path );
 201                         }
 202                         wfDebug( __METHOD__ . ": released lock on key $locksKey.\n" );
 203                 }
 204
 205                 // Unlock all of the active lock record keys...
 206                 $this->releaseMutexes( $memc, $keys );
 207
 208                 return $status;
 209         }
 210
 211         /**
 212          * @see QuorumLockManager::releaseAllLocks()
 213          * @return Status
 214          */
 215         protected function releaseAllLocks() {
 216                 return Status::newGood(); // not supported
 217         }
 218
 219         /**
 220          * @see QuorumLockManager::isServerUp()
 221          * @return bool
 222          */
 223         protected function isServerUp( $lockSrv ) {
 224                 return (bool)$this->getCache( $lockSrv );
 225         }
 226
 227         /**
 228          * Get the MemcachedBagOStuff object for a $lockSrv
 229          *
 230          * @param $lockSrv string Server name
 231          * @return MemcachedBagOStuff|null
 232          */
 233         protected function getCache( $lockSrv ) {
 234                 $memc = null;
 235                 if ( isset( $this->bagOStuffs[$lockSrv] ) ) {
 236                         $memc = $this->bagOStuffs[$lockSrv];
 237                         if ( !isset( $this->serversUp[$lockSrv] ) ) {
 238                                 $this->serversUp[$lockSrv] = $memc->set( 'MemcLockManager:ping', 1, 1 );
 239                                 if ( !$this->serversUp[$lockSrv] ) {
 240                                         trigger_error( __METHOD__ . ": Could not contact $lockSrv.", E_USER_WARNING );
 241                                 }
 242                         }
 243                         if ( !$this->serversUp[$lockSrv] ) {
 244                                 return null; // server appears to be down
 245                         }
 246                 }
 247                 return $memc;
 248         }
 249
 250         /**
 251          * @param $path string
 252          * @return string
 253          */
 254         protected function recordKeyForPath( $path ) {
 255                 $hash = LockManager::sha1Base36( $path );
 256                 list( $db, $prefix ) = wfSplitWikiID( $this->wikiId );
 257                 return wfForeignMemcKey( $db, $prefix, __CLASS__, 'locks', $hash );
 258         }
 259
 260         /**
 261          * @param $memc MemcachedBagOStuff
 262          * @param $keys Array List of keys to acquire
 263          * @return bool
 264          */
 265         protected function acquireMutexes( MemcachedBagOStuff $memc, array $keys ) {
 266                 $lockedKeys = array();
 267
 268                 // Acquire the keys in lexicographical order, to avoid deadlock problems.
 269                 // If P1 is waiting to acquire a key P2 has, P2 can't also be waiting for a key P1 has.
 270                 sort( $keys );
 271
 272                 // Try to quickly loop to acquire the keys, but back off after a few rounds.
 273                 // This reduces memcached spam, especially in the rare case where a server acquires
 274                 // some lock keys and dies without releasing them. Lock keys expire after a few minutes.
 275                 $rounds = 0;
 276                 $start = microtime( true );
 277                 do {
 278                         if ( ( ++$rounds % 4 ) == 0 ) {
 279                                 usleep( 1000*50 ); // 50 ms
 280                         }
 281                         foreach ( array_diff( $keys, $lockedKeys ) as $key ) {
 282                                 if ( $memc->add( "$key:mutex", 1, 180 ) ) { // lock record
 283                                         $lockedKeys[] = $key;
 284                                 } else {
 285                                         continue; // acquire in order
 286                                 }
 287                         }
 288                 } while ( count( $lockedKeys ) < count( $keys ) && ( microtime( true ) - $start ) <= 6 );
 289
 290                 if ( count( $lockedKeys ) != count( $keys ) ) {
 291                         $this->releaseMutexes( $lockedKeys ); // failed; release what was locked
 292                         return false;
 293                 }
 294
 295                 return true;
 296         }
 297
 298         /**
 299          * @param $memc MemcachedBagOStuff
 300          * @param $keys Array List of acquired keys
 301          * @return void
 302          */
 303         protected function releaseMutexes( MemcachedBagOStuff $memc, array $keys ) {
 304                 foreach ( $keys as $key ) {
 305                         $memc->delete( "$key:mutex" );
 306                 }
 307         }
 308
 309         /**
 310          * Make sure remaining locks get cleared for sanity
 311          */
 312         function __destruct() {
 313                 while ( count( $this->locksHeld ) ) {
 314                         foreach ( $this->locksHeld as $path => $locks ) {
 315                                 $this->doUnlock( array( $path ), self::LOCK_EX );
 316                                 $this->doUnlock( array( $path ), self::LOCK_SH );
 317                         }
 318                 }
 319         }
 320 }