includes/db/loadbalancer/LBFactory.php

   1 <?php
   2 /**
   3  * Generator of database load balancing objects.
   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 Database
  22  */
  23
  24 /**
  25  * An interface for generating database load balancers
  26  * @ingroup Database
  27  */
  28 abstract class LBFactory {
  29         /** @var LBFactory */
  30         private static $instance;
  31
  32         /**
  33          * Disables all access to the load balancer, will cause all database access
  34          * to throw a DBAccessError
  35          */
  36         public static function disableBackend() {
  37                 global $wgLBFactoryConf;
  38                 self::$instance = new LBFactoryFake( $wgLBFactoryConf );
  39         }
  40
  41         /**
  42          * Get an LBFactory instance
  43          *
  44          * @return LBFactory
  45          */
  46         public static function singleton() {
  47                 global $wgLBFactoryConf;
  48
  49                 if ( is_null( self::$instance ) ) {
  50                         $class = self::getLBFactoryClass( $wgLBFactoryConf );
  51
  52                         self::$instance = new $class( $wgLBFactoryConf );
  53                 }
  54
  55                 return self::$instance;
  56         }
  57
  58         /**
  59          * Returns the LBFactory class to use and the load balancer configuration.
  60          *
  61          * @param array $config (e.g. $wgLBFactoryConf)
  62          * @return string Class name
  63          */
  64         public static function getLBFactoryClass( array $config ) {
  65                 // For configuration backward compatibility after removing
  66                 // underscores from class names in MediaWiki 1.23.
  67                 $bcClasses = array(
  68                         'LBFactory_Simple' => 'LBFactorySimple',
  69                         'LBFactory_Single' => 'LBFactorySingle',
  70                         'LBFactory_Multi' => 'LBFactoryMulti',
  71                         'LBFactory_Fake' => 'LBFactoryFake',
  72                 );
  73
  74                 $class = $config['class'];
  75
  76                 if ( isset( $bcClasses[$class] ) ) {
  77                         $class = $bcClasses[$class];
  78                         wfDeprecated(
  79                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
  80                                 '1.23'
  81                         );
  82                 }
  83
  84                 return $class;
  85         }
  86
  87         /**
  88          * Shut down, close connections and destroy the cached instance.
  89          */
  90         public static function destroyInstance() {
  91                 if ( self::$instance ) {
  92                         self::$instance->shutdown();
  93                         self::$instance->forEachLBCallMethod( 'closeAll' );
  94                         self::$instance = null;
  95                 }
  96         }
  97
  98         /**
  99          * Set the instance to be the given object
 100          *
 101          * @param LBFactory $instance
 102          */
 103         public static function setInstance( $instance ) {
 104                 self::destroyInstance();
 105                 self::$instance = $instance;
 106         }
 107
 108         /**
 109          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
 110          * @param array $conf
 111          */
 112         abstract public function __construct( array $conf );
 113
 114         /**
 115          * Create a new load balancer object. The resulting object will be untracked,
 116          * not chronology-protected, and the caller is responsible for cleaning it up.
 117          *
 118          * @param bool|string $wiki Wiki ID, or false for the current wiki
 119          * @return LoadBalancer
 120          */
 121         abstract public function newMainLB( $wiki = false );
 122
 123         /**
 124          * Get a cached (tracked) load balancer object.
 125          *
 126          * @param bool|string $wiki Wiki ID, or false for the current wiki
 127          * @return LoadBalancer
 128          */
 129         abstract public function getMainLB( $wiki = false );
 130
 131         /**
 132          * Create a new load balancer for external storage. The resulting object will be
 133          * untracked, not chronology-protected, and the caller is responsible for
 134          * cleaning it up.
 135          *
 136          * @param string $cluster External storage cluster, or false for core
 137          * @param bool|string $wiki Wiki ID, or false for the current wiki
 138          * @return LoadBalancer
 139          */
 140         abstract protected function newExternalLB( $cluster, $wiki = false );
 141
 142         /**
 143          * Get a cached (tracked) load balancer for external storage
 144          *
 145          * @param string $cluster External storage cluster, or false for core
 146          * @param bool|string $wiki Wiki ID, or false for the current wiki
 147          * @return LoadBalancer
 148          */
 149         abstract public function &getExternalLB( $cluster, $wiki = false );
 150
 151         /**
 152          * Execute a function for each tracked load balancer
 153          * The callback is called with the load balancer as the first parameter,
 154          * and $params passed as the subsequent parameters.
 155          *
 156          * @param callable $callback
 157          * @param array $params
 158          */
 159         abstract public function forEachLB( $callback, array $params = array() );
 160
 161         /**
 162          * Prepare all tracked load balancers for shutdown
 163          * STUB
 164          */
 165         public function shutdown() {
 166         }
 167
 168         /**
 169          * Call a method of each tracked load balancer
 170          *
 171          * @param string $methodName
 172          * @param array $args
 173          */
 174         private function forEachLBCallMethod( $methodName, array $args = array() ) {
 175                 $this->forEachLB( function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 176                         call_user_func_array( array( $loadBalancer, $methodName ), $args );
 177                 }, array( $methodName, $args ) );
 178         }
 179
 180         /**
 181          * Commit on all connections. Done for two reasons:
 182          * 1. To commit changes to the masters.
 183          * 2. To release the snapshot on all connections, master and slave.
 184          */
 185         public function commitAll() {
 186                 $this->forEachLBCallMethod( 'commitAll' );
 187         }
 188
 189         /**
 190          * Commit changes on all master connections
 191          */
 192         public function commitMasterChanges() {
 193                 $this->forEachLBCallMethod( 'commitMasterChanges' );
 194         }
 195
 196         /**
 197          * Rollback changes on all master connections
 198          * @since 1.23
 199          */
 200         public function rollbackMasterChanges() {
 201                 $this->forEachLBCallMethod( 'rollbackMasterChanges' );
 202         }
 203
 204         /**
 205          * Detemine if any master connection has pending changes.
 206          * @since 1.23
 207          * @return bool
 208          */
 209         public function hasMasterChanges() {
 210                 $ret = false;
 211                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 212                         $ret = $ret || $lb->hasMasterChanges();
 213                 } );
 214                 return $ret;
 215         }
 216 }
 217
 218 /**
 219  * Exception class for attempted DB access
 220  */
 221 class DBAccessError extends MWException {
 222         public function __construct() {
 223                 parent::__construct( "Mediawiki tried to access the database via wfGetDB(). " .
 224                         "This is not allowed." );
 225         }
 226 }