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 run immediately if no DB writes are pending. Otherwise, they run when:
  34  *   - a) Any waitForReplication() call if no writes are pending on any DB
  35  *   - b) A commit happens on Maintenance::getDB( DB_MASTER ) if no writes are pending on any DB
  36  *   - c) EnqueueableDataUpdate tasks may enqueue on commit of Maintenance::getDB( DB_MASTER )
  37  *   - d) At the completion of Maintenance::execute()
  38  *
  39  * When updates are deferred, they use a FIFO queue (one for pre-send and one for post-send).
  40  *
  41  * @since 1.19
  42  */
  43 class DeferredUpdates {
  44         /** @var DeferrableUpdate[] Updates to be deferred until before request end */
  45         private static $preSendUpdates = [];
  46         /** @var DeferrableUpdate[] Updates to be deferred until after request end */
  47         private static $postSendUpdates = [];
  48
  49         const ALL = 0; // all updates; in web requests, use only after flushing the output buffer
  50         const PRESEND = 1; // for updates that should run before flushing output buffer
  51         const POSTSEND = 2; // for updates that should run after flushing output buffer
  52
  53         const BIG_QUEUE_SIZE = 100;
  54
  55         /** @var array|null Information about the current execute() call or null if not running */
  56         private static $executeContext;
  57
  58         /**
  59          * Add an update to the deferred list to be run later by execute()
  60          *
  61          * In CLI mode, callback magic will also be used to run updates when safe
  62          *
  63          * @param DeferrableUpdate $update Some object that implements doUpdate()
  64          * @param integer $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
  65          */
  66         public static function addUpdate( DeferrableUpdate $update, $stage = self::POSTSEND ) {
  67                 global $wgCommandLineMode;
  68
  69                 // This is a sub-DeferredUpdate, run it right after its parent update
  70                 if ( self::$executeContext && self::$executeContext['stage'] >= $stage ) {
  71                         self::$executeContext['subqueue'][] = $update;
  72                         return;
  73                 }
  74
  75                 if ( $stage === self::PRESEND ) {
  76                         self::push( self::$preSendUpdates, $update );
  77                 } else {
  78                         self::push( self::$postSendUpdates, $update );
  79                 }
  80
  81                 // Try to run the updates now if in CLI mode and no transaction is active.
  82                 // This covers scripts that don't/barely use the DB but make updates to other stores.
  83                 if ( $wgCommandLineMode ) {
  84                         self::tryOpportunisticExecute( 'run' );
  85                 }
  86         }
  87
  88         /**
  89          * Add a callable update. In a lot of cases, we just need a callback/closure,
  90          * defining a new DeferrableUpdate object is not necessary
  91          *
  92          * @see MWCallableUpdate::__construct()
  93          *
  94          * @param callable $callable
  95          * @param integer $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
  96          * @param IDatabase|null $dbw Abort if this DB is rolled back [optional] (since 1.28)
  97          */
  98         public static function addCallableUpdate(
  99                 $callable, $stage = self::POSTSEND, IDatabase $dbw = null
 100         ) {
 101                 self::addUpdate( new MWCallableUpdate( $callable, wfGetCaller(), $dbw ), $stage );
 102         }
 103
 104         /**
 105          * Do any deferred updates and clear the list
 106          *
 107          * @param string $mode Use "enqueue" to use the job queue when possible [Default: "run"]
 108          * @param integer $stage DeferredUpdates constant (PRESEND, POSTSEND, or ALL) (since 1.27)
 109          */
 110         public static function doUpdates( $mode = 'run', $stage = self::ALL ) {
 111                 $stageEffective = ( $stage === self::ALL ) ? self::POSTSEND : $stage;
 112
 113                 if ( $stage === self::ALL || $stage === self::PRESEND ) {
 114                         self::execute( self::$preSendUpdates, $mode, $stageEffective );
 115                 }
 116
 117                 if ( $stage === self::ALL || $stage == self::POSTSEND ) {
 118                         self::execute( self::$postSendUpdates, $mode, $stageEffective );
 119                 }
 120         }
 121
 122         /**
 123          * @param DeferrableUpdate[] $queue
 124          * @param DeferrableUpdate $update
 125          */
 126         private static function push( array &$queue, DeferrableUpdate $update ) {
 127                 if ( $update instanceof MergeableUpdate ) {
 128                         $class = get_class( $update ); // fully-qualified class
 129                         if ( isset( $queue[$class] ) ) {
 130                                 /** @var $existingUpdate MergeableUpdate */
 131                                 $existingUpdate = $queue[$class];
 132                                 $existingUpdate->merge( $update );
 133                         } else {
 134                                 $queue[$class] = $update;
 135                         }
 136                 } else {
 137                         $queue[] = $update;
 138                 }
 139         }
 140
 141         /**
 142          * @param DeferrableUpdate[] &$queue List of DeferrableUpdate objects
 143          * @param string $mode Use "enqueue" to use the job queue when possible
 144          * @param integer $stage Class constant (PRESEND, POSTSEND) (since 1.28)
 145          * @throws ErrorPageError Happens on top-level calls
 146          * @throws Exception Happens on second-level calls
 147          */
 148         public static function execute( array &$queue, $mode, $stage ) {
 149                 $services = MediaWikiServices::getInstance();
 150                 $stats = $services->getStatsdDataFactory();
 151                 $lbFactory = $services->getDBLoadBalancerFactory();
 152                 $method = RequestContext::getMain()->getRequest()->getMethod();
 153
 154                 /** @var ErrorPageError $reportableError */
 155                 $reportableError = null;
 156                 /** @var DeferrableUpdate[] $updates Snapshot of queue */
 157                 $updates = $queue;
 158
 159                 // Keep doing rounds of updates until none get enqueued...
 160                 while ( $updates ) {
 161                         $queue = []; // clear the queue
 162
 163                         if ( $mode === 'enqueue' ) {
 164                                 try {
 165                                         // Push enqueuable updates to the job queue and get the rest
 166                                         $updates = self::enqueueUpdates( $updates );
 167                                 } catch ( Exception $e ) {
 168                                         // Let other updates have a chance to run if this failed
 169                                         MWExceptionHandler::rollbackMasterChangesAndLog( $e );
 170                                 }
 171                         }
 172
 173                         // Order will be DataUpdate followed by generic DeferrableUpdate tasks
 174                         $updatesByType = [ 'data' => [], 'generic' => [] ];
 175                         foreach ( $updates as $du ) {
 176                                 $updatesByType[$du instanceof DataUpdate ? 'data' : 'generic'][] = $du;
 177                                 $name = ( $du instanceof DeferrableCallback )
 178                                         ? get_class( $du ) . '-' . $du->getOrigin()
 179                                         : get_class( $du );
 180                                 $stats->increment( 'deferred_updates.' . $method . '.' . $name );
 181                         }
 182
 183                         // Execute all remaining tasks...
 184                         foreach ( $updatesByType as $updatesForType ) {
 185                                 foreach ( $updatesForType as $update ) {
 186                                         self::$executeContext = [
 187                                                 'update' => $update,
 188                                                 'stage' => $stage,
 189                                                 'subqueue' => []
 190                                         ];
 191                                         /** @var DeferrableUpdate $update */
 192                                         $guiError = self::runUpdate( $update, $lbFactory, $stage );
 193                                         $reportableError = $reportableError ?: $guiError;
 194                                         // Do the subqueue updates for $update until there are none
 195                                         while ( self::$executeContext['subqueue'] ) {
 196                                                 $subUpdate = reset( self::$executeContext['subqueue'] );
 197                                                 $firstKey = key( self::$executeContext['subqueue'] );
 198                                                 unset( self::$executeContext['subqueue'][$firstKey] );
 199
 200                                                 $guiError = self::runUpdate( $subUpdate, $lbFactory, $stage );
 201                                                 $reportableError = $reportableError ?: $guiError;
 202                                         }
 203                                         self::$executeContext = null;
 204                                 }
 205                         }
 206
 207                         $updates = $queue; // new snapshot of queue (check for new entries)
 208                 }
 209
 210                 if ( $reportableError ) {
 211                         throw $reportableError; // throw the first of any GUI errors
 212                 }
 213         }
 214
 215         /**
 216          * @param DeferrableUpdate $update
 217          * @param LBFactory $lbFactory
 218          * @param integer $stage
 219          * @return ErrorPageError|null
 220          */
 221         private static function runUpdate( DeferrableUpdate $update, LBFactory $lbFactory, $stage ) {
 222                 $guiError = null;
 223                 try {
 224                         $fnameTrxOwner = get_class( $update ) . '::doUpdate';
 225                         $lbFactory->beginMasterChanges( $fnameTrxOwner );
 226                         $update->doUpdate();
 227                         $lbFactory->commitMasterChanges( $fnameTrxOwner );
 228                 } catch ( Exception $e ) {
 229                         // Reporting GUI exceptions does not work post-send
 230                         if ( $e instanceof ErrorPageError && $stage === self::PRESEND ) {
 231                                 $guiError = $e;
 232                         }
 233                         MWExceptionHandler::rollbackMasterChangesAndLog( $e );
 234                 }
 235
 236                 return $guiError;
 237         }
 238
 239         /**
 240          * Run all deferred updates immediately if there are no DB writes active
 241          *
 242          * If $mode is 'run' but there are busy databates, EnqueueableDataUpdate
 243          * tasks will be enqueued anyway for the sake of progress.
 244          *
 245          * @param string $mode Use "enqueue" to use the job queue when possible
 246          * @return bool Whether updates were allowed to run
 247          * @since 1.28
 248          */
 249         public static function tryOpportunisticExecute( $mode = 'run' ) {
 250                 // execute() loop is already running
 251                 if ( self::$executeContext ) {
 252                         return false;
 253                 }
 254
 255                 // Avoiding running updates without them having outer scope
 256                 if ( !self::getBusyDbConnections() ) {
 257                         self::doUpdates( $mode );
 258                         return true;
 259                 }
 260
 261                 if ( self::pendingUpdatesCount() >= self::BIG_QUEUE_SIZE ) {
 262                         // If we cannot run the updates with outer transaction context, try to
 263                         // at least enqueue all the updates that support queueing to job queue
 264                         self::$preSendUpdates = self::enqueueUpdates( self::$preSendUpdates );
 265                         self::$postSendUpdates = self::enqueueUpdates( self::$postSendUpdates );
 266                 }
 267
 268                 return !self::pendingUpdatesCount();
 269         }
 270
 271         /**
 272          * Enqueue a job for each EnqueueableDataUpdate item and return the other items
 273          *
 274          * @param DeferrableUpdate[] $updates A list of deferred update instances
 275          * @return DeferrableUpdate[] Remaining updates that do not support being queued
 276          */
 277         private static function enqueueUpdates( array $updates ) {
 278                 $remaining = [];
 279
 280                 foreach ( $updates as $update ) {
 281                         if ( $update instanceof EnqueueableDataUpdate ) {
 282                                 $spec = $update->getAsJobSpecification();
 283                                 JobQueueGroup::singleton( $spec['wiki'] )->push( $spec['job'] );
 284                         } else {
 285                                 $remaining[] = $update;
 286                         }
 287                 }
 288
 289                 return $remaining;
 290         }
 291
 292         /**
 293          * @return integer Number of enqueued updates
 294          * @since 1.28
 295          */
 296         public static function pendingUpdatesCount() {
 297                 return count( self::$preSendUpdates ) + count( self::$postSendUpdates );
 298         }
 299
 300         /**
 301          * Clear all pending updates without performing them. Generally, you don't
 302          * want or need to call this. Unit tests need it though.
 303          */
 304         public static function clearPendingUpdates() {
 305                 self::$preSendUpdates = [];
 306                 self::$postSendUpdates = [];
 307         }
 308
 309         /**
 310          * @return IDatabase[] Connection where commit() cannot be called yet
 311          */
 312         private static function getBusyDbConnections() {
 313                 $connsBusy = [];
 314
 315                 $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 316                 $lbFactory->forEachLB( function ( LoadBalancer $lb ) use ( &$connsBusy ) {
 317                         $lb->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$connsBusy ) {
 318                                 if ( $conn->writesOrCallbacksPending() || $conn->explicitTrxActive() ) {
 319                                         $connsBusy[] = $conn;
 320                                 }
 321                         } );
 322                 } );
 323
 324                 return $connsBusy;
 325         }
 326 }