CategoryMembershipChangeJob.php

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<?php
use MediaWiki\MediaWikiServices;

class CategoryMembershipChangeJob extends Job {
    private $ticket;

    const ENQUEUE_FUDGE_SEC = 60;

    public function __construct( Title $title, array $params ) {
        parent::__construct( 'categoryMembershipChange', $title, $params );
        // Only need one job per page. Note that ENQUEUE_FUDGE_SEC handles races where an
        // older revision job gets inserted while the newer revision job is de-duplicated.
        $this->removeDuplicates = true;
    }

    public function run() {
        $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
        $lb = $lbFactory->getMainLB();
        $dbw = $lb->getConnection( DB_MASTER );

        $this->ticket = $lbFactory->getEmptyTransactionTicket( __METHOD__ );

        $page = WikiPage::newFromID( $this->params['pageId'], WikiPage::READ_LATEST );
        if ( !$page ) {
            $this->setLastError( "Could not find page #{$this->params['pageId']}" );
            return false; // deleted?
        }

        // Use a named lock so that jobs for this page see each others' changes
        $lockKey = "CategoryMembershipUpdates:{$page->getId()}";
        $scopedLock = $dbw->getScopedLockAndFlush( $lockKey, __METHOD__, 3 );
        if ( !$scopedLock ) {
            $this->setLastError( "Could not acquire lock '$lockKey'" );
            return false;
        }

        $dbr = $lb->getConnection( DB_REPLICA, [ 'recentchanges' ] );
        // Wait till the replica DB is caught up so that jobs for this page see each others' changes
        if ( !$lb->safeWaitForMasterPos( $dbr ) ) {
            $this->setLastError( "Timed out while waiting for replica DB to catch up" );
            return false;
        }
        // Clear any stale REPEATABLE-READ snapshot
        $dbr->flushSnapshot( __METHOD__ );

        $cutoffUnix = wfTimestamp( TS_UNIX, $this->params['revTimestamp'] );
        // Using ENQUEUE_FUDGE_SEC handles jobs inserted out of revision order due to the delay
        // between COMMIT and actual enqueueing of the CategoryMembershipChangeJob job.
        $cutoffUnix -= self::ENQUEUE_FUDGE_SEC;

        // Get the newest revision that has a SRC_CATEGORIZE row...
        $row = $dbr->selectRow(
            [ 'revision', 'recentchanges' ],
            [ 'rev_timestamp', 'rev_id' ],
            [
                'rev_page' => $page->getId(),
                'rev_timestamp >= ' . $dbr->addQuotes( $dbr->timestamp( $cutoffUnix ) )
            ],
            __METHOD__,
            [ 'ORDER BY' => 'rev_timestamp DESC, rev_id DESC' ],
            [
                'recentchanges' => [
                    'INNER JOIN',
                    [
                        'rc_this_oldid = rev_id',
                        'rc_source' => RecentChange::SRC_CATEGORIZE,
                        // Allow rc_cur_id or rc_timestamp index usage
                        'rc_cur_id = rev_page',
                        'rc_timestamp >= rev_timestamp'
                    ]
                ]
            ]
        );
        // Only consider revisions newer than any such revision
        if ( $row ) {
            $cutoffUnix = wfTimestamp( TS_UNIX, $row->rev_timestamp );
            $lastRevId = (int)$row->rev_id;
        } else {
            $lastRevId = 0;
        }

        // Find revisions to this page made around and after this revision which lack category
        // notifications in recent changes. This lets jobs pick up were the last one left off.
        $encCutoff = $dbr->addQuotes( $dbr->timestamp( $cutoffUnix ) );
        $res = $dbr->select(
            'revision',
            Revision::selectFields(),
            [
                'rev_page' => $page->getId(),
                "rev_timestamp > $encCutoff" .
                    " OR (rev_timestamp = $encCutoff AND rev_id > $lastRevId)"
            ],
            __METHOD__,
            [ 'ORDER BY' => 'rev_timestamp ASC, rev_id ASC' ]
        );

        // Apply all category updates in revision timestamp order
        foreach ( $res as $row ) {
            $this->notifyUpdatesForRevision( $lbFactory, $page, Revision::newFromRow( $row ) );
        }

        return true;
    }

    protected function notifyUpdatesForRevision(
        LBFactory $lbFactory, WikiPage $page, Revision $newRev
    ) {
        $config = RequestContext::getMain()->getConfig();
        $title = $page->getTitle();

        // Get the new revision
        if ( !$newRev->getContent() ) {
            return; // deleted?
        }

        // Get the prior revision (the same for null edits)
        if ( $newRev->getParentId() ) {
            $oldRev = Revision::newFromId( $newRev->getParentId(), Revision::READ_LATEST );
            if ( !$oldRev->getContent() ) {
                return; // deleted?
            }
        } else {
            $oldRev = null;
        }

        // Parse the new revision and get the categories
        $categoryChanges = $this->getExplicitCategoriesChanges( $title, $newRev, $oldRev );
        list( $categoryInserts, $categoryDeletes ) = $categoryChanges;
        if ( !$categoryInserts && !$categoryDeletes ) {
            return; // nothing to do
        }

        $catMembChange = new CategoryMembershipChange( $title, $newRev );
        $catMembChange->checkTemplateLinks();

        $batchSize = $config->get( 'UpdateRowsPerQuery' );
        $insertCount = 0;

        foreach ( $categoryInserts as $categoryName ) {
            $categoryTitle = Title::makeTitle( NS_CATEGORY, $categoryName );
            $catMembChange->triggerCategoryAddedNotification( $categoryTitle );
            if ( $insertCount++ && ( $insertCount % $batchSize ) == 0 ) {
                $lbFactory->commitAndWaitForReplication( __METHOD__, $this->ticket );
            }
        }

        foreach ( $categoryDeletes as $categoryName ) {
            $categoryTitle = Title::makeTitle( NS_CATEGORY, $categoryName );
            $catMembChange->triggerCategoryRemovedNotification( $categoryTitle );
            if ( $insertCount++ && ( $insertCount++ % $batchSize ) == 0 ) {
                $lbFactory->commitAndWaitForReplication( __METHOD__, $this->ticket );
            }
        }
    }

    private function getExplicitCategoriesChanges(
        Title $title, Revision $newRev, Revision $oldRev = null
    ) {
        // Inject the same timestamp for both revision parses to avoid seeing category changes
        // due to time-based parser functions. Inject the same page title for the parses too.
        // Note that REPEATABLE-READ makes template/file pages appear unchanged between parses.
        $parseTimestamp = $newRev->getTimestamp();
        // Parse the old rev and get the categories. Do not use link tables as that
        // assumes these updates are perfectly FIFO and that link tables are always
        // up to date, neither of which are true.
        $oldCategories = $oldRev
            ? $this->getCategoriesAtRev( $title, $oldRev, $parseTimestamp )
            : [];
        // Parse the new revision and get the categories
        $newCategories = $this->getCategoriesAtRev( $title, $newRev, $parseTimestamp );

        $categoryInserts = array_values( array_diff( $newCategories, $oldCategories ) );
        $categoryDeletes = array_values( array_diff( $oldCategories, $newCategories ) );

        return [ $categoryInserts, $categoryDeletes ];
    }

    private function getCategoriesAtRev( Title $title, Revision $rev, $parseTimestamp ) {
        $content = $rev->getContent();
        $options = $content->getContentHandler()->makeParserOptions( 'canonical' );
        $options->setTimestamp( $parseTimestamp );
        // This could possibly use the parser cache if it checked the revision ID,
        // but that's more complicated than it's worth.
        $output = $content->getParserOutput( $title, $rev->getId(), $options );

        // array keys will cast numeric category names to ints
        // so we need to cast them back to strings to avoid breaking things!
        return array_map( 'strval', array_keys( $output->getCategories() ) );
    }

    public function getDeduplicationInfo() {
        $info = parent::getDeduplicationInfo();
        unset( $info['params']['revTimestamp'] ); // first job wins

        return $info;
    }
}