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. These two modes are defined via PRESEND and POSTSEND constants, the latter
  31  * being the default for addUpdate() and addCallableUpdate().
  32  *
  33  * Updates that work through this system will be more likely to complete by the time the client
  34  * makes their next request after this one than with the JobQueue system.
  35  *
  36  * In CLI mode, updates run immediately if no DB writes are pending. Otherwise, they run when:
  37  *   - a) Any waitForReplication() call if no writes are pending on any DB
  38  *   - b) A commit happens on Maintenance::getDB( DB_MASTER ) if no writes are pending on any DB
  39  *   - c) EnqueueableDataUpdate tasks may enqueue on commit of Maintenance::getDB( DB_MASTER )
  40  *   - d) At the completion of Maintenance::execute()
  41  *
  42  * When updates are deferred, they go into one two FIFO "top-queues" (one for pre-send and one
  43  * for post-send). Updates enqueued *during* doUpdate() of a "top" update go into the "sub-queue"
  44  * for that update. After that method finishes, the sub-queue is run until drained. This continues
  45  * for each top-queue job until the entire top queue is drained. This happens for the pre-send
  46  * top-queue, and later on, the post-send top-queue, in execute().
  47  *
  48  * @since 1.19
  49  */
  50 class DeferredUpdates {
  51         /** @var DeferrableUpdate[] Updates to be deferred until before request end */
  52         private static $preSendUpdates = [];
  53         /** @var DeferrableUpdate[] Updates to be deferred until after request end */
  54         private static $postSendUpdates = [];
  55         /** @var bool Whether to just run updates in addUpdate() */
  56         private static $immediateMode = false;
  57
  58         const ALL = 0; // all updates; in web requests, use only after flushing the output buffer
  59         const PRESEND = 1; // for updates that should run before flushing output buffer
  60         const POSTSEND = 2; // for updates that should run after flushing output buffer
  61
  62         const BIG_QUEUE_SIZE = 100;
  63
  64         /** @var array|null Information about the current execute() call or null if not running */
  65         private static $executeContext;
  66
  67         /**
  68          * Add an update to the deferred list to be run later by execute()
  69          *
  70          * In CLI mode, callback magic will also be used to run updates when safe
  71          *
  72          * @param DeferrableUpdate $update Some object that implements doUpdate()
  73          * @param integer $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
  74          */
  75         public static function addUpdate( DeferrableUpdate $update, $stage = self::POSTSEND ) {
  76                 global $wgCommandLineMode;
  77
  78                 // This is a sub-DeferredUpdate, run it right after its parent update
  79                 if ( self::$executeContext && self::$executeContext['stage'] >= $stage ) {
  80                         self::$executeContext['subqueue'][] = $update;
  81                         return;
  82                 }
  83
  84                 if ( $stage === self::PRESEND ) {
  85                         self::push( self::$preSendUpdates, $update );
  86                 } else {
  87                         self::push( self::$postSendUpdates, $update );
  88                 }
  89
  90                 if ( self::$immediateMode ) {
  91                         // No more explicit doUpdates() calls will happen, so run this now
  92                         self::doUpdates( 'run' );
  93                         return;
  94                 }
  95
  96                 // Try to run the updates now if in CLI mode and no transaction is active.
  97                 // This covers scripts that don't/barely use the DB but make updates to other stores.
  98                 if ( $wgCommandLineMode ) {
  99                         self::tryOpportunisticExecute( 'run' );
 100                 }
 101         }
 102
 103         /**
 104          * Add a callable update. In a lot of cases, we just need a callback/closure,
 105          * defining a new DeferrableUpdate object is not necessary
 106          *
 107          * @see MWCallableUpdate::__construct()
 108          *
 109          * @param callable $callable
 110          * @param integer $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
 111          * @param IDatabase|null $dbw Abort if this DB is rolled back [optional] (since 1.28)
 112          */
 113         public static function addCallableUpdate(
 114                 $callable, $stage = self::POSTSEND, IDatabase $dbw = null
 115         ) {
 116                 self::addUpdate( new MWCallableUpdate( $callable, wfGetCaller(), $dbw ), $stage );
 117         }
 118
 119         /**
 120          * Do any deferred updates and clear the list
 121          *
 122          * @param string $mode Use "enqueue" to use the job queue when possible [Default: "run"]
 123          * @param integer $stage DeferredUpdates constant (PRESEND, POSTSEND, or ALL) (since 1.27)
 124          */
 125         public static function doUpdates( $mode = 'run', $stage = self::ALL ) {
 126                 $stageEffective = ( $stage === self::ALL ) ? self::POSTSEND : $stage;
 127
 128                 if ( $stage === self::ALL || $stage === self::PRESEND ) {
 129                         self::execute( self::$preSendUpdates, $mode, $stageEffective );
 130                 }
 131
 132                 if ( $stage === self::ALL || $stage == self::POSTSEND ) {
 133                         self::execute( self::$postSendUpdates, $mode, $stageEffective );
 134                 }
 135         }
 136
 137         /**
 138          * @param bool $value Whether to just immediately run updates in addUpdate()
 139          * @since 1.28
 140          */
 141         public static function setImmediateMode( $value ) {
 142                 self::$immediateMode = (bool)$value;
 143         }
 144
 145         /**
 146          * @param DeferrableUpdate[] $queue
 147          * @param DeferrableUpdate $update
 148          */
 149         private static function push( array &$queue, DeferrableUpdate $update ) {
 150                 if ( $update instanceof MergeableUpdate ) {
 151                         $class = get_class( $update ); // fully-qualified class
 152                         if ( isset( $queue[$class] ) ) {
 153                                 /** @var $existingUpdate MergeableUpdate */
 154                                 $existingUpdate = $queue[$class];
 155                                 $existingUpdate->merge( $update );
 156                         } else {
 157                                 $queue[$class] = $update;
 158                         }
 159                 } else {
 160                         $queue[] = $update;
 161                 }
 162         }
 163
 164         /**
 165          * Immediately run/queue a list of updates
 166          *
 167          * @param DeferrableUpdate[] &$queue List of DeferrableUpdate objects
 168          * @param string $mode Use "enqueue" to use the job queue when possible
 169          * @param integer $stage Class constant (PRESEND, POSTSEND) (since 1.28)
 170          * @throws ErrorPageError Happens on top-level calls
 171          * @throws Exception Happens on second-level calls
 172          */
 173         protected static function execute( array &$queue, $mode, $stage ) {
 174                 $services = MediaWikiServices::getInstance();
 175                 $stats = $services->getStatsdDataFactory();
 176                 $lbFactory = $services->getDBLoadBalancerFactory();
 177                 $method = RequestContext::getMain()->getRequest()->getMethod();
 178
 179                 $ticket = $lbFactory->getEmptyTransactionTicket( __METHOD__ );
 180
 181                 /** @var ErrorPageError $reportableError */
 182                 $reportableError = null;
 183                 /** @var DeferrableUpdate[] $updates Snapshot of queue */
 184                 $updates = $queue;
 185
 186                 // Keep doing rounds of updates until none get enqueued...
 187                 while ( $updates ) {
 188                         $queue = []; // clear the queue
 189
 190                         if ( $mode === 'enqueue' ) {
 191                                 try {
 192                                         // Push enqueuable updates to the job queue and get the rest
 193                                         $updates = self::enqueueUpdates( $updates );
 194                                 } catch ( Exception $e ) {
 195                                         // Let other updates have a chance to run if this failed
 196                                         MWExceptionHandler::rollbackMasterChangesAndLog( $e );
 197                                 }
 198                         }
 199
 200                         // Order will be DataUpdate followed by generic DeferrableUpdate tasks
 201                         $updatesByType = [ 'data' => [], 'generic' => [] ];
 202                         foreach ( $updates as $du ) {
 203                                 if ( $du instanceof DataUpdate ) {
 204                                         $du->setTransactionTicket( $ticket );
 205                                         $updatesByType['data'][] = $du;
 206                                 } else {
 207                                         $updatesByType['generic'][] = $du;
 208                                 }
 209
 210                                 $name = ( $du instanceof DeferrableCallback )
 211                                         ? get_class( $du ) . '-' . $du->getOrigin()
 212                                         : get_class( $du );
 213                                 $stats->increment( 'deferred_updates.' . $method . '.' . $name );
 214                         }
 215
 216                         // Execute all remaining tasks...
 217                         foreach ( $updatesByType as $updatesForType ) {
 218                                 foreach ( $updatesForType as $update ) {
 219                                         self::$executeContext = [
 220                                                 'update' => $update,
 221                                                 'stage' => $stage,
 222                                                 'subqueue' => []
 223                                         ];
 224                                         /** @var DeferrableUpdate $update */
 225                                         $guiError = self::runUpdate( $update, $lbFactory, $stage );
 226                                         $reportableError = $reportableError ?: $guiError;
 227                                         // Do the subqueue updates for $update until there are none
 228                                         while ( self::$executeContext['subqueue'] ) {
 229                                                 $subUpdate = reset( self::$executeContext['subqueue'] );
 230                                                 $firstKey = key( self::$executeContext['subqueue'] );
 231                                                 unset( self::$executeContext['subqueue'][$firstKey] );
 232
 233                                                 if ( $subUpdate instanceof DataUpdate ) {
 234                                                         $subUpdate->setTransactionTicket( $ticket );
 235                                                 }
 236
 237                                                 $guiError = self::runUpdate( $subUpdate, $lbFactory, $stage );
 238                                                 $reportableError = $reportableError ?: $guiError;
 239                                         }
 240                                         self::$executeContext = null;
 241                                 }
 242                         }
 243
 244                         $updates = $queue; // new snapshot of queue (check for new entries)
 245                 }
 246
 247                 if ( $reportableError ) {
 248                         throw $reportableError; // throw the first of any GUI errors
 249                 }
 250         }
 251
 252         /**
 253          * @param DeferrableUpdate $update
 254          * @param LBFactory $lbFactory
 255          * @param integer $stage
 256          * @return ErrorPageError|null
 257          */
 258         private static function runUpdate( DeferrableUpdate $update, LBFactory $lbFactory, $stage ) {
 259                 $guiError = null;
 260                 try {
 261                         $fnameTrxOwner = get_class( $update ) . '::doUpdate';
 262                         $lbFactory->beginMasterChanges( $fnameTrxOwner );
 263                         $update->doUpdate();
 264                         $lbFactory->commitMasterChanges( $fnameTrxOwner );
 265                 } catch ( Exception $e ) {
 266                         // Reporting GUI exceptions does not work post-send
 267                         if ( $e instanceof ErrorPageError && $stage === self::PRESEND ) {
 268                                 $guiError = $e;
 269                         }
 270                         MWExceptionHandler::rollbackMasterChangesAndLog( $e );
 271                 }
 272
 273                 return $guiError;
 274         }
 275
 276         /**
 277          * Run all deferred updates immediately if there are no DB writes active
 278          *
 279          * If $mode is 'run' but there are busy databates, EnqueueableDataUpdate
 280          * tasks will be enqueued anyway for the sake of progress.
 281          *
 282          * @param string $mode Use "enqueue" to use the job queue when possible
 283          * @return bool Whether updates were allowed to run
 284          * @since 1.28
 285          */
 286         public static function tryOpportunisticExecute( $mode = 'run' ) {
 287                 // execute() loop is already running
 288                 if ( self::$executeContext ) {
 289                         return false;
 290                 }
 291
 292                 // Avoiding running updates without them having outer scope
 293                 if ( !self::getBusyDbConnections() ) {
 294                         self::doUpdates( $mode );
 295                         return true;
 296                 }
 297
 298                 if ( self::pendingUpdatesCount() >= self::BIG_QUEUE_SIZE ) {
 299                         // If we cannot run the updates with outer transaction context, try to
 300                         // at least enqueue all the updates that support queueing to job queue
 301                         self::$preSendUpdates = self::enqueueUpdates( self::$preSendUpdates );
 302                         self::$postSendUpdates = self::enqueueUpdates( self::$postSendUpdates );
 303                 }
 304
 305                 return !self::pendingUpdatesCount();
 306         }
 307
 308         /**
 309          * Enqueue a job for each EnqueueableDataUpdate item and return the other items
 310          *
 311          * @param DeferrableUpdate[] $updates A list of deferred update instances
 312          * @return DeferrableUpdate[] Remaining updates that do not support being queued
 313          */
 314         private static function enqueueUpdates( array $updates ) {
 315                 $remaining = [];
 316
 317                 foreach ( $updates as $update ) {
 318                         if ( $update instanceof EnqueueableDataUpdate ) {
 319                                 $spec = $update->getAsJobSpecification();
 320                                 JobQueueGroup::singleton( $spec['wiki'] )->push( $spec['job'] );
 321                         } else {
 322                                 $remaining[] = $update;
 323                         }
 324                 }
 325
 326                 return $remaining;
 327         }
 328
 329         /**
 330          * @return integer Number of enqueued updates
 331          * @since 1.28
 332          */
 333         public static function pendingUpdatesCount() {
 334                 return count( self::$preSendUpdates ) + count( self::$postSendUpdates );
 335         }
 336
 337         /**
 338          * Clear all pending updates without performing them. Generally, you don't
 339          * want or need to call this. Unit tests need it though.
 340          */
 341         public static function clearPendingUpdates() {
 342                 self::$preSendUpdates = [];
 343                 self::$postSendUpdates = [];
 344         }
 345
 346         /**
 347          * @return IDatabase[] Connection where commit() cannot be called yet
 348          */
 349         private static function getBusyDbConnections() {
 350                 $connsBusy = [];
 351
 352                 $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 353                 $lbFactory->forEachLB( function ( LoadBalancer $lb ) use ( &$connsBusy ) {
 354                         $lb->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$connsBusy ) {
 355                                 if ( $conn->writesOrCallbacksPending() || $conn->explicitTrxActive() ) {
 356                                         $connsBusy[] = $conn;
 357                                 }
 358                         } );
 359                 } );
 360
 361                 return $connsBusy;
 362         }
 363 }