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          * Construct a factory based on a configuration array (typically from $wgLBFactoryConf)
  34          * @param array $conf
  35          */
  36         public function __construct( array $conf ) {
  37         }
  38
  39         /**
  40          * Disables all access to the load balancer, will cause all database access
  41          * to throw a DBAccessError
  42          */
  43         public static function disableBackend() {
  44                 global $wgLBFactoryConf;
  45                 self::$instance = new LBFactoryFake( $wgLBFactoryConf );
  46         }
  47
  48         /**
  49          * Get an LBFactory instance
  50          *
  51          * @return LBFactory
  52          */
  53         public static function singleton() {
  54                 global $wgLBFactoryConf;
  55
  56                 if ( is_null( self::$instance ) ) {
  57                         $class = self::getLBFactoryClass( $wgLBFactoryConf );
  58
  59                         self::$instance = new $class( $wgLBFactoryConf );
  60                 }
  61
  62                 return self::$instance;
  63         }
  64
  65         /**
  66          * Returns the LBFactory class to use and the load balancer configuration.
  67          *
  68          * @param array $config (e.g. $wgLBFactoryConf)
  69          * @return string Class name
  70          */
  71         public static function getLBFactoryClass( array $config ) {
  72                 // For configuration backward compatibility after removing
  73                 // underscores from class names in MediaWiki 1.23.
  74                 $bcClasses = array(
  75                         'LBFactory_Simple' => 'LBFactorySimple',
  76                         'LBFactory_Single' => 'LBFactorySingle',
  77                         'LBFactory_Multi' => 'LBFactoryMulti',
  78                         'LBFactory_Fake' => 'LBFactoryFake',
  79                 );
  80
  81                 $class = $config['class'];
  82
  83                 if ( isset( $bcClasses[$class] ) ) {
  84                         $class = $bcClasses[$class];
  85                         wfDeprecated(
  86                                 '$wgLBFactoryConf must be updated. See RELEASE-NOTES for details',
  87                                 '1.23'
  88                         );
  89                 }
  90
  91                 return $class;
  92         }
  93
  94         /**
  95          * Shut down, close connections and destroy the cached instance.
  96          */
  97         public static function destroyInstance() {
  98                 if ( self::$instance ) {
  99                         self::$instance->shutdown();
 100                         self::$instance->forEachLBCallMethod( 'closeAll' );
 101                         self::$instance = null;
 102                 }
 103         }
 104
 105         /**
 106          * Set the instance to be the given object
 107          *
 108          * @param LBFactory $instance
 109          */
 110         public static function setInstance( $instance ) {
 111                 self::destroyInstance();
 112                 self::$instance = $instance;
 113         }
 114
 115         /**
 116          * Create a new load balancer object. The resulting object will be untracked,
 117          * not chronology-protected, and the caller is responsible for cleaning it up.
 118          *
 119          * @param bool|string $wiki Wiki ID, or false for the current wiki
 120          * @return LoadBalancer
 121          */
 122         abstract public function newMainLB( $wiki = false );
 123
 124         /**
 125          * Get a cached (tracked) load balancer object.
 126          *
 127          * @param bool|string $wiki Wiki ID, or false for the current wiki
 128          * @return LoadBalancer
 129          */
 130         abstract public function getMainLB( $wiki = false );
 131
 132         /**
 133          * Create a new load balancer for external storage. The resulting object will be
 134          * untracked, not chronology-protected, and the caller is responsible for
 135          * cleaning it up.
 136          *
 137          * @param string $cluster External storage cluster, or false for core
 138          * @param bool|string $wiki Wiki ID, or false for the current wiki
 139          * @return LoadBalancer
 140          */
 141         abstract protected function newExternalLB( $cluster, $wiki = false );
 142
 143         /**
 144          * Get a cached (tracked) load balancer for external storage
 145          *
 146          * @param string $cluster External storage cluster, or false for core
 147          * @param bool|string $wiki Wiki ID, or false for the current wiki
 148          * @return LoadBalancer
 149          */
 150         abstract public function &getExternalLB( $cluster, $wiki = false );
 151
 152         /**
 153          * Execute a function for each tracked load balancer
 154          * The callback is called with the load balancer as the first parameter,
 155          * and $params passed as the subsequent parameters.
 156          *
 157          * @param callable $callback
 158          * @param array $params
 159          */
 160         abstract public function forEachLB( $callback, array $params = array() );
 161
 162         /**
 163          * Prepare all tracked load balancers for shutdown
 164          * STUB
 165          */
 166         public function shutdown() {
 167         }
 168
 169         /**
 170          * Call a method of each tracked load balancer
 171          *
 172          * @param string $methodName
 173          * @param array $args
 174          */
 175         private function forEachLBCallMethod( $methodName, array $args = array() ) {
 176                 $this->forEachLB( function ( LoadBalancer $loadBalancer, $methodName, array $args ) {
 177                         call_user_func_array( array( $loadBalancer, $methodName ), $args );
 178                 }, array( $methodName, $args ) );
 179         }
 180
 181         /**
 182          * Commit on all connections. Done for two reasons:
 183          * 1. To commit changes to the masters.
 184          * 2. To release the snapshot on all connections, master and slave.
 185          */
 186         public function commitAll() {
 187                 $this->forEachLBCallMethod( 'commitAll' );
 188         }
 189
 190         /**
 191          * Commit changes on all master connections
 192          */
 193         public function commitMasterChanges() {
 194                 $this->forEachLBCallMethod( 'commitMasterChanges' );
 195         }
 196
 197         /**
 198          * Rollback changes on all master connections
 199          * @since 1.23
 200          */
 201         public function rollbackMasterChanges() {
 202                 $this->forEachLBCallMethod( 'rollbackMasterChanges' );
 203         }
 204
 205         /**
 206          * Determine if any master connection has pending changes
 207          * @return bool
 208          * @since 1.23
 209          */
 210         public function hasMasterChanges() {
 211                 $ret = false;
 212                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 213                         $ret = $ret || $lb->hasMasterChanges();
 214                 } );
 215
 216                 return $ret;
 217         }
 218
 219         /**
 220          * Detemine if any lagged slave connection was used
 221          * @since 1.27
 222          * @return bool
 223          */
 224         public function laggedSlaveUsed() {
 225                 $ret = false;
 226                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 227                         $ret = $ret || $lb->laggedSlaveUsed();
 228                 } );
 229
 230                 return $ret;
 231         }
 232
 233         /**
 234          * Determine if any master connection has pending/written changes from this request
 235          * @return bool
 236          * @since 1.27
 237          */
 238         public function hasOrMadeRecentMasterChanges() {
 239                 $ret = false;
 240                 $this->forEachLB( function ( LoadBalancer $lb ) use ( &$ret ) {
 241                         $ret = $ret || $lb->hasOrMadeRecentMasterChanges();
 242                 } );
 243                 return $ret;
 244         }
 245 }
 246
 247 /**
 248  * Exception class for attempted DB access
 249  */
 250 class DBAccessError extends MWException {
 251         public function __construct() {
 252                 parent::__construct( "Mediawiki tried to access the database via wfGetDB(). " .
 253                         "This is not allowed." );
 254         }
 255 }