includes/libs/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 = [
  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 MemcachedBagOStuff[] Map of (server name => MemcachedBagOStuff) */
  47         protected $cacheServers = [];
  48         /** @var HashBagOStuff Server status cache */
  49         protected $statusCache;
  50
  51         /**
  52          * Construct a new instance from configuration.
  53          *
  54          * @param array $config Parameters include:
  55          *   - lockServers  : Associative array of server names to "<IP>:<port>" strings.
  56          *   - srvsByBucket : Array of 1-16 consecutive integer keys, starting from 0,
  57          *                    each having an odd-numbered list of server names (peers) as values.
  58          *   - memcConfig   : Configuration array for MemcachedBagOStuff::construct() with an
  59          *                    additional 'class' parameter specifying which MemcachedBagOStuff
  60          *                    subclass to use. The server names will be injected. [optional]
  61          * @throws Exception
  62          */
  63         public function __construct( array $config ) {
  64                 parent::__construct( $config );
  65
  66                 // Sanitize srvsByBucket config to prevent PHP errors
  67                 $this->srvsByBucket = array_filter( $config['srvsByBucket'], 'is_array' );
  68                 $this->srvsByBucket = array_values( $this->srvsByBucket ); // consecutive
  69
  70                 $memcConfig = isset( $config['memcConfig'] ) ? $config['memcConfig'] : [];
  71                 $memcConfig += [ 'class' => 'MemcachedPhpBagOStuff' ]; // default
  72
  73                 $class = $memcConfig['class'];
  74                 if ( !is_subclass_of( $class, 'MemcachedBagOStuff' ) ) {
  75                         throw new InvalidArgumentException( "$class is not of type MemcachedBagOStuff." );
  76                 }
  77
  78                 foreach ( $config['lockServers'] as $name => $address ) {
  79                         $params = [ 'servers' => [ $address ] ] + $memcConfig;
  80                         $this->cacheServers[$name] = new $class( $params );
  81                 }
  82
  83                 $this->statusCache = new HashBagOStuff();
  84         }
  85
  86         protected function getLocksOnServer( $lockSrv, array $pathsByType ) {
  87                 $status = StatusValue::newGood();
  88
  89                 $memc = $this->getCache( $lockSrv );
  90                 // List of affected paths
  91                 $paths = call_user_func_array( 'array_merge', array_values( $pathsByType ) );
  92                 $paths = array_unique( $paths );
  93                 // List of affected lock record keys
  94                 $keys = array_map( [ $this, 'recordKeyForPath' ], $paths );
  95
  96                 // Lock all of the active lock record keys...
  97                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
  98                         foreach ( $paths as $path ) {
  99                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 100                         }
 101
 102                         return $status;
 103                 }
 104
 105                 // Fetch all the existing lock records...
 106                 $lockRecords = $memc->getMulti( $keys );
 107
 108                 $now = time();
 109                 // Check if the requested locks conflict with existing ones...
 110                 foreach ( $pathsByType as $type => $paths ) {
 111                         foreach ( $paths as $path ) {
 112                                 $locksKey = $this->recordKeyForPath( $path );
 113                                 $locksHeld = isset( $lockRecords[$locksKey] )
 114                                         ? self::sanitizeLockArray( $lockRecords[$locksKey] )
 115                                         : self::newLockArray(); // init
 116                                 foreach ( $locksHeld[self::LOCK_EX] as $session => $expiry ) {
 117                                         if ( $expiry < $now ) { // stale?
 118                                                 unset( $locksHeld[self::LOCK_EX][$session] );
 119                                         } elseif ( $session !== $this->session ) {
 120                                                 $status->fatal( 'lockmanager-fail-acquirelock', $path );
 121                                         }
 122                                 }
 123                                 if ( $type === self::LOCK_EX ) {
 124                                         foreach ( $locksHeld[self::LOCK_SH] as $session => $expiry ) {
 125                                                 if ( $expiry < $now ) { // stale?
 126                                                         unset( $locksHeld[self::LOCK_SH][$session] );
 127                                                 } elseif ( $session !== $this->session ) {
 128                                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 129                                                 }
 130                                         }
 131                                 }
 132                                 if ( $status->isOK() ) {
 133                                         // Register the session in the lock record array
 134                                         $locksHeld[$type][$this->session] = $now + $this->lockTTL;
 135                                         // We will update this record if none of the other locks conflict
 136                                         $lockRecords[$locksKey] = $locksHeld;
 137                                 }
 138                         }
 139                 }
 140
 141                 // If there were no lock conflicts, update all the lock records...
 142                 if ( $status->isOK() ) {
 143                         foreach ( $paths as $path ) {
 144                                 $locksKey = $this->recordKeyForPath( $path );
 145                                 $locksHeld = $lockRecords[$locksKey];
 146                                 $ok = $memc->set( $locksKey, $locksHeld, self::MAX_LOCK_TTL );
 147                                 if ( !$ok ) {
 148                                         $status->fatal( 'lockmanager-fail-acquirelock', $path );
 149                                 } else {
 150                                         $this->logger->debug( __METHOD__ . ": acquired lock on key $locksKey.\n" );
 151                                 }
 152                         }
 153                 }
 154
 155                 // Unlock all of the active lock record keys...
 156                 $this->releaseMutexes( $memc, $keys );
 157
 158                 return $status;
 159         }
 160
 161         protected function freeLocksOnServer( $lockSrv, array $pathsByType ) {
 162                 $status = StatusValue::newGood();
 163
 164                 $memc = $this->getCache( $lockSrv );
 165                 // List of affected paths
 166                 $paths = call_user_func_array( 'array_merge', array_values( $pathsByType ) );
 167                 $paths = array_unique( $paths );
 168                 // List of affected lock record keys
 169                 $keys = array_map( [ $this, 'recordKeyForPath' ], $paths );
 170
 171                 // Lock all of the active lock record keys...
 172                 if ( !$this->acquireMutexes( $memc, $keys ) ) {
 173                         foreach ( $paths as $path ) {
 174                                 $status->fatal( 'lockmanager-fail-releaselock', $path );
 175                         }
 176
 177                         return $status;
 178                 }
 179
 180                 // Fetch all the existing lock records...
 181                 $lockRecords = $memc->getMulti( $keys );
 182
 183                 // Remove the requested locks from all records...
 184                 foreach ( $pathsByType as $type => $paths ) {
 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 = $this->sanitizeLockArray( $lockRecords[$locksKey] );
 192                                 if ( isset( $locksHeld[$type][$this->session] ) ) {
 193                                         unset( $locksHeld[$type][$this->session] ); // unregister this session
 194                                         $lockRecords[$locksKey] = $locksHeld;
 195                                 } else {
 196                                         $status->warning( 'lockmanager-fail-releaselock', $path );
 197                                 }
 198                         }
 199                 }
 200
 201                 // Persist the new lock record values...
 202                 foreach ( $paths as $path ) {
 203                         $locksKey = $this->recordKeyForPath( $path );
 204                         if ( !isset( $lockRecords[$locksKey] ) ) {
 205                                 continue; // nothing to do
 206                         }
 207                         $locksHeld = $lockRecords[$locksKey];
 208                         if ( $locksHeld === $this->newLockArray() ) {
 209                                 $ok = $memc->delete( $locksKey );
 210                         } else {
 211                                 $ok = $memc->set( $locksKey, $locksHeld, self::MAX_LOCK_TTL );
 212                         }
 213                         if ( $ok ) {
 214                                 $this->logger->debug( __METHOD__ . ": released lock on key $locksKey.\n" );
 215                         } else {
 216                                 $status->fatal( 'lockmanager-fail-releaselock', $path );
 217                         }
 218                 }
 219
 220                 // Unlock all of the active lock record keys...
 221                 $this->releaseMutexes( $memc, $keys );
 222
 223                 return $status;
 224         }
 225
 226         /**
 227          * @see QuorumLockManager::releaseAllLocks()
 228          * @return StatusValue
 229          */
 230         protected function releaseAllLocks() {
 231                 return StatusValue::newGood(); // not supported
 232         }
 233
 234         /**
 235          * @see QuorumLockManager::isServerUp()
 236          * @param string $lockSrv
 237          * @return bool
 238          */
 239         protected function isServerUp( $lockSrv ) {
 240                 return (bool)$this->getCache( $lockSrv );
 241         }
 242
 243         /**
 244          * Get the MemcachedBagOStuff object for a $lockSrv
 245          *
 246          * @param string $lockSrv Server name
 247          * @return MemcachedBagOStuff|null
 248          */
 249         protected function getCache( $lockSrv ) {
 250                 if ( !isset( $this->cacheServers[$lockSrv] ) ) {
 251                         throw new InvalidArgumentException( "Invalid cache server '$lockSrv'." );
 252                 }
 253
 254                 $online = $this->statusCache->get( "online:$lockSrv" );
 255                 if ( $online === false ) {
 256                         $online = $this->cacheServers[$lockSrv]->set( __CLASS__ . ':ping', 1, 1 );
 257                         if ( !$online ) { // server down?
 258                                 $this->logger->warning( __METHOD__ . ": Could not contact $lockSrv." );
 259                         }
 260                         $this->statusCache->set( "online:$lockSrv", (int)$online, 30 );
 261                 }
 262
 263                 return $online ? $this->cacheServers[$lockSrv] : null;
 264         }
 265
 266         /**
 267          * @param string $path
 268          * @return string
 269          */
 270         protected function recordKeyForPath( $path ) {
 271                 return implode( ':', [ __CLASS__, 'locks', $this->sha1Base36Absolute( $path ) ] );
 272         }
 273
 274         /**
 275          * @return array An empty lock structure for a key
 276          */
 277         protected function newLockArray() {
 278                 return [ self::LOCK_SH => [], self::LOCK_EX => [] ];
 279         }
 280
 281         /**
 282          * @param array $a
 283          * @return array An empty lock structure for a key
 284          */
 285         protected function sanitizeLockArray( $a ) {
 286                 if ( is_array( $a ) && isset( $a[self::LOCK_EX] ) && isset( $a[self::LOCK_SH] ) ) {
 287                         return $a;
 288                 }
 289
 290                 $this->logger->error( __METHOD__ . ": reset invalid lock array." );
 291
 292                 return $this->newLockArray();
 293         }
 294
 295         /**
 296          * @param MemcachedBagOStuff $memc
 297          * @param array $keys List of keys to acquire
 298          * @return bool
 299          */
 300         protected function acquireMutexes( MemcachedBagOStuff $memc, array $keys ) {
 301                 $lockedKeys = [];
 302
 303                 // Acquire the keys in lexicographical order, to avoid deadlock problems.
 304                 // If P1 is waiting to acquire a key P2 has, P2 can't also be waiting for a key P1 has.
 305                 sort( $keys );
 306
 307                 // Try to quickly loop to acquire the keys, but back off after a few rounds.
 308                 // This reduces memcached spam, especially in the rare case where a server acquires
 309                 // some lock keys and dies without releasing them. Lock keys expire after a few minutes.
 310                 $loop = new WaitConditionLoop(
 311                         function () use ( $memc, $keys, &$lockedKeys ) {
 312                                 foreach ( array_diff( $keys, $lockedKeys ) as $key ) {
 313                                         if ( $memc->add( "$key:mutex", 1, 180 ) ) { // lock record
 314                                                 $lockedKeys[] = $key;
 315                                         }
 316                                 }
 317
 318                                 return array_diff( $keys, $lockedKeys )
 319                                         ? WaitConditionLoop::CONDITION_CONTINUE
 320                                         : true;
 321                         },
 322                         3.0 // timeout
 323                 );
 324                 $loop->invoke();
 325
 326                 if ( count( $lockedKeys ) != count( $keys ) ) {
 327                         $this->releaseMutexes( $memc, $lockedKeys ); // failed; release what was locked
 328                         return false;
 329                 }
 330
 331                 return true;
 332         }
 333
 334         /**
 335          * @param MemcachedBagOStuff $memc
 336          * @param array $keys List of acquired keys
 337          */
 338         protected function releaseMutexes( MemcachedBagOStuff $memc, array $keys ) {
 339                 foreach ( $keys as $key ) {
 340                         $memc->delete( "$key:mutex" );
 341                 }
 342         }
 343
 344         /**
 345          * Make sure remaining locks get cleared for sanity
 346          */
 347         function __destruct() {
 348                 while ( count( $this->locksHeld ) ) {
 349                         foreach ( $this->locksHeld as $path => $locks ) {
 350                                 $this->doUnlock( [ $path ], self::LOCK_EX );
 351                                 $this->doUnlock( [ $path ], self::LOCK_SH );
 352                         }
 353                 }
 354         }
 355 }