includes/deferred/DeferredUpdates.php

   1 <?php
   2 /**
   3  * Interface and manager for deferred updates.
   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  */
  22 use MediaWiki\MediaWikiServices;
  23
  24 /**
  25  * Class for managing the deferred updates
  26  *
  27  * In web request mode, deferred updates can be run at the end of the request, either before or
  28  * after the HTTP response has been sent. In either case, they run after the DB commit step. If
  29  * an update runs after the response is sent, it will not block clients. If sent before, it will
  30  * run synchronously. If such an update works via queueing, it will be more likely to complete by
  31  * the time the client makes their next request after this one.
  32  *
  33  * In CLI mode, updates are only deferred until the current wiki has no DB write transaction
  34  * active within this request.
  35  *
  36  * When updates are deferred, they use a FIFO queue (one for pre-send and one for post-send).
  37  *
  38  * @since 1.19
  39  */
  40 class DeferredUpdates {
  41         /** @var DeferrableUpdate[] Updates to be deferred until before request end */
  42         private static $preSendUpdates = [];
  43         /** @var DeferrableUpdate[] Updates to be deferred until after request end */
  44         private static $postSendUpdates = [];
  45
  46         const ALL = 0; // all updates
  47         const PRESEND = 1; // for updates that should run before flushing output buffer
  48         const POSTSEND = 2; // for updates that should run after flushing output buffer
  49
  50         const BIG_QUEUE_SIZE = 100;
  51
  52         /**
  53          * Add an update to the deferred list to be run later by execute()
  54          *
  55          * In CLI mode, callback magic will also be used to run updates when safe
  56          *
  57          * @param DeferrableUpdate $update Some object that implements doUpdate()
  58          * @param integer $type DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
  59          */
  60         public static function addUpdate( DeferrableUpdate $update, $type = self::POSTSEND ) {
  61                 global $wgCommandLineMode;
  62
  63                 if ( $type === self::PRESEND ) {
  64                         self::push( self::$preSendUpdates, $update );
  65                 } else {
  66                         self::push( self::$postSendUpdates, $update );
  67                 }
  68
  69                 // Try to run the updates now if in CLI mode and no transaction is active.
  70                 // This covers scripts that don't/barely use the DB but make updates to other stores.
  71                 if ( $wgCommandLineMode ) {
  72                         self::tryOpportunisticExecute( 'run' );
  73                 }
  74         }
  75
  76         /**
  77          * Add a callable update. In a lot of cases, we just need a callback/closure,
  78          * defining a new DeferrableUpdate object is not necessary
  79          *
  80          * @see MWCallableUpdate::__construct()
  81          *
  82          * @param callable $callable
  83          * @param integer $type DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
  84          * @param IDatabase|null $dbw Abort if this DB is rolled back [optional] (since 1.28)
  85          */
  86         public static function addCallableUpdate(
  87                 $callable, $type = self::POSTSEND, IDatabase $dbw = null
  88         ) {
  89                 self::addUpdate( new MWCallableUpdate( $callable, wfGetCaller(), $dbw ), $type );
  90         }
  91
  92         /**
  93          * Do any deferred updates and clear the list
  94          *
  95          * @param string $mode Use "enqueue" to use the job queue when possible [Default: "run"]
  96          * @param integer $type DeferredUpdates constant (PRESEND, POSTSEND, or ALL) (since 1.27)
  97          */
  98         public static function doUpdates( $mode = 'run', $type = self::ALL ) {
  99                 if ( $type === self::ALL || $type == self::PRESEND ) {
 100                         self::execute( self::$preSendUpdates, $mode );
 101                 }
 102
 103                 if ( $type === self::ALL || $type == self::POSTSEND ) {
 104                         self::execute( self::$postSendUpdates, $mode );
 105                 }
 106         }
 107
 108         private static function push( array &$queue, DeferrableUpdate $update ) {
 109                 if ( $update instanceof MergeableUpdate ) {
 110                         $class = get_class( $update ); // fully-qualified class
 111                         if ( isset( $queue[$class] ) ) {
 112                                 /** @var $existingUpdate MergeableUpdate */
 113                                 $existingUpdate = $queue[$class];
 114                                 $existingUpdate->merge( $update );
 115                         } else {
 116                                 $queue[$class] = $update;
 117                         }
 118                 } else {
 119                         $queue[] = $update;
 120                 }
 121         }
 122
 123         public static function execute( array &$queue, $mode ) {
 124                 $stats = \MediaWiki\MediaWikiServices::getInstance()->getStatsdDataFactory();
 125                 $method = RequestContext::getMain()->getRequest()->getMethod();
 126
 127                 $updates = $queue; // snapshot of queue
 128                 // Keep doing rounds of updates until none get enqueued
 129                 while ( count( $updates ) ) {
 130                         $queue = []; // clear the queue
 131                         /** @var DataUpdate[] $dataUpdates */
 132                         $dataUpdates = [];
 133                         /** @var DeferrableUpdate[] $otherUpdates */
 134                         $otherUpdates = [];
 135                         foreach ( $updates as $update ) {
 136                                 if ( $update instanceof DataUpdate ) {
 137                                         $dataUpdates[] = $update;
 138                                 } else {
 139                                         $otherUpdates[] = $update;
 140                                 }
 141
 142                                 $name = $update instanceof DeferrableCallback
 143                                         ? get_class( $update ) . '-' . $update->getOrigin()
 144                                         : get_class( $update );
 145                                 $stats->increment( 'deferred_updates.' . $method . '.' . $name );
 146                         }
 147
 148                         // Delegate DataUpdate execution to the DataUpdate class
 149                         try {
 150                                 DataUpdate::runUpdates( $dataUpdates, $mode );
 151                         } catch ( Exception $e ) {
 152                                 // Let the other updates occur if these had to rollback
 153                                 MWExceptionHandler::logException( $e );
 154                         }
 155                         // Execute the non-DataUpdate tasks
 156                         foreach ( $otherUpdates as $update ) {
 157                                 try {
 158                                         $update->doUpdate();
 159                                         wfGetLBFactory()->commitMasterChanges( __METHOD__ );
 160                                 } catch ( Exception $e ) {
 161                                         // We don't want exceptions thrown during deferred updates to
 162                                         // be reported to the user since the output is already sent
 163                                         if ( !$e instanceof ErrorPageError ) {
 164                                                 MWExceptionHandler::logException( $e );
 165                                         }
 166                                         // Make sure incomplete transactions are not committed and end any
 167                                         // open atomic sections so that other DB updates have a chance to run
 168                                         wfGetLBFactory()->rollbackMasterChanges( __METHOD__ );
 169                                 }
 170                         }
 171
 172                         $updates = $queue; // new snapshot of queue (check for new entries)
 173                 }
 174         }
 175
 176         /**
 177          * Run all deferred updates immediately if there are no DB writes active
 178          *
 179          * If $mode is 'run' but there are busy databates, EnqueueableDataUpdate
 180          * tasks will be enqueued anyway for the sake of progress.
 181          *
 182          * @param string $mode Use "enqueue" to use the job queue when possible
 183          * @return bool Whether updates were allowed to run
 184          * @since 1.28
 185          */
 186         public static function tryOpportunisticExecute( $mode = 'run' ) {
 187                 if ( !self::getBusyDbConnections() ) {
 188                         self::doUpdates( $mode );
 189                         return true;
 190                 }
 191
 192                 if ( self::pendingUpdatesCount() >= self::BIG_QUEUE_SIZE ) {
 193                         // If we cannot run the updates with outer transaction context, try to
 194                         // at least enqueue all the updates that support queueing to job queue
 195                         self::$preSendUpdates = self::enqueueUpdates( self::$preSendUpdates );
 196                         self::$postSendUpdates = self::enqueueUpdates( self::$postSendUpdates );
 197                 }
 198
 199                 return !self::pendingUpdatesCount();
 200         }
 201
 202         /**
 203          * Enqueue a job for each EnqueueableDataUpdate item and return the other items
 204          *
 205          * @param DeferrableUpdate[] $updates A list of deferred update instances
 206          * @return DeferrableUpdate[] Remaining updates that do not support being queued
 207          */
 208         private static function enqueueUpdates( array $updates ) {
 209                 $remaining = [];
 210
 211                 foreach ( $updates as $update ) {
 212                         if ( $update instanceof EnqueueableDataUpdate ) {
 213                                 $spec = $update->getAsJobSpecification();
 214                                 JobQueueGroup::singleton( $spec['wiki'] )->push( $spec['job'] );
 215                         } else {
 216                                 $remaining[] = $update;
 217                         }
 218                 }
 219
 220                 return $remaining;
 221         }
 222
 223         /**
 224          * @return integer Number of enqueued updates
 225          * @since 1.28
 226          */
 227         public static function pendingUpdatesCount() {
 228                 return count( self::$preSendUpdates ) + count( self::$postSendUpdates );
 229         }
 230
 231         /**
 232          * Clear all pending updates without performing them. Generally, you don't
 233          * want or need to call this. Unit tests need it though.
 234          */
 235         public static function clearPendingUpdates() {
 236                 self::$preSendUpdates = [];
 237                 self::$postSendUpdates = [];
 238         }
 239
 240         /**
 241          * Set the rollback/commit watcher on a DB to trigger update runs when safe
 242          *
 243          * @TODO: use this to replace DB logic in push()
 244          * @param LoadBalancer $lb
 245          * @since 1.28
 246          */
 247         public static function installDBListener( LoadBalancer $lb ) {
 248                 static $triggers = [ IDatabase::TRIGGER_COMMIT, IDatabase::TRIGGER_ROLLBACK ];
 249                 // Hook into active master connections to find a moment where no writes are pending
 250                 $lb->setTransactionListener(
 251                         __METHOD__,
 252                         function ( $trigger, IDatabase $conn ) use ( $triggers ) {
 253                                 global $wgCommandLineMode;
 254
 255                                 if ( $wgCommandLineMode && in_array( $trigger, $triggers ) ) {
 256                                         DeferredUpdates::tryOpportunisticExecute();
 257                                 }
 258                         }
 259                 );
 260         }
 261
 262         /**
 263          * @return IDatabase[] Connection where commit() cannot be called yet
 264          */
 265         private static function getBusyDbConnections() {
 266                 $connsBusy = [];
 267
 268                 $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 269                 $lbFactory->forEachLB( function ( LoadBalancer $lb ) use ( &$connsBusy ) {
 270                         $lb->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$connsBusy ) {
 271                                 if ( $conn->writesOrCallbacksPending() || $conn->explicitTrxActive() ) {
 272                                         $connsBusy[] = $conn;
 273                                 }
 274                         } );
 275                 } );
 276
 277                 return $connsBusy;
 278         }
 279 }