Type check the APC value in LoadBalancer::doWait()

[mediawiki.git] / includes / deferred / DeferredUpdates.php

<?php
/**
 * Interface and manager for deferred updates.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 */
use MediaWiki\MediaWikiServices;
use Wikimedia\Rdbms\LBFactory;

/**
 * Class for managing the deferred updates
 *
 * In web request mode, deferred updates can be run at the end of the request, either before or
 * after the HTTP response has been sent. In either case, they run after the DB commit step. If
 * an update runs after the response is sent, it will not block clients. If sent before, it will
 * run synchronously. These two modes are defined via PRESEND and POSTSEND constants, the latter
 * being the default for addUpdate() and addCallableUpdate().
 *
 * Updates that work through this system will be more likely to complete by the time the client
 * makes their next request after this one than with the JobQueue system.
 *
 * In CLI mode, updates run immediately if no DB writes are pending. Otherwise, they run when:
 *   - a) Any waitForReplication() call if no writes are pending on any DB
 *   - b) A commit happens on Maintenance::getDB( DB_MASTER ) if no writes are pending on any DB
 *   - c) EnqueueableDataUpdate tasks may enqueue on commit of Maintenance::getDB( DB_MASTER )
 *   - d) At the completion of Maintenance::execute()
 *
 * When updates are deferred, they go into one two FIFO "top-queues" (one for pre-send and one
 * for post-send). Updates enqueued *during* doUpdate() of a "top" update go into the "sub-queue"
 * for that update. After that method finishes, the sub-queue is run until drained. This continues
 * for each top-queue job until the entire top queue is drained. This happens for the pre-send
 * top-queue, and later on, the post-send top-queue, in execute().
 *
 * @since 1.19
 */
class DeferredUpdates {
        /** @var DeferrableUpdate[] Updates to be deferred until before request end */
        private static $preSendUpdates = [];
        /** @var DeferrableUpdate[] Updates to be deferred until after request end */
        private static $postSendUpdates = [];
        /** @var bool Whether to just run updates in addUpdate() */
        private static $immediateMode = false;

        const ALL = 0; // all updates; in web requests, use only after flushing the output buffer
        const PRESEND = 1; // for updates that should run before flushing output buffer
        const POSTSEND = 2; // for updates that should run after flushing output buffer

        const BIG_QUEUE_SIZE = 100;

        /** @var array|null Information about the current execute() call or null if not running */
        private static $executeContext;

        /**
         * Add an update to the deferred list to be run later by execute()
         *
         * In CLI mode, callback magic will also be used to run updates when safe
         *
         * @param DeferrableUpdate $update Some object that implements doUpdate()
         * @param integer $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
         */
        public static function addUpdate( DeferrableUpdate $update, $stage = self::POSTSEND ) {
                global $wgCommandLineMode;

                // This is a sub-DeferredUpdate, run it right after its parent update
                if ( self::$executeContext && self::$executeContext['stage'] >= $stage ) {
                        self::$executeContext['subqueue'][] = $update;
                        return;
                }

                if ( $stage === self::PRESEND ) {
                        self::push( self::$preSendUpdates, $update );
                } else {
                        self::push( self::$postSendUpdates, $update );
                }

                if ( self::$immediateMode ) {
                        // No more explicit doUpdates() calls will happen, so run this now
                        self::doUpdates( 'run' );
                        return;
                }

                // Try to run the updates now if in CLI mode and no transaction is active.
                // This covers scripts that don't/barely use the DB but make updates to other stores.
                if ( $wgCommandLineMode ) {
                        self::tryOpportunisticExecute( 'run' );
                }
        }

        /**
         * Add a callable update. In a lot of cases, we just need a callback/closure,
         * defining a new DeferrableUpdate object is not necessary
         *
         * @see MWCallableUpdate::__construct()
         *
         * @param callable $callable
         * @param integer $stage DeferredUpdates constant (PRESEND or POSTSEND) (since 1.27)
         * @param IDatabase|null $dbw Abort if this DB is rolled back [optional] (since 1.28)
         */
        public static function addCallableUpdate(
                $callable, $stage = self::POSTSEND, IDatabase $dbw = null
        ) {
                self::addUpdate( new MWCallableUpdate( $callable, wfGetCaller(), $dbw ), $stage );
        }

        /**
         * Do any deferred updates and clear the list
         *
         * @param string $mode Use "enqueue" to use the job queue when possible [Default: "run"]
         * @param integer $stage DeferredUpdates constant (PRESEND, POSTSEND, or ALL) (since 1.27)
         */
        public static function doUpdates( $mode = 'run', $stage = self::ALL ) {
                $stageEffective = ( $stage === self::ALL ) ? self::POSTSEND : $stage;

                if ( $stage === self::ALL || $stage === self::PRESEND ) {
                        self::execute( self::$preSendUpdates, $mode, $stageEffective );
                }

                if ( $stage === self::ALL || $stage == self::POSTSEND ) {
                        self::execute( self::$postSendUpdates, $mode, $stageEffective );
                }
        }

        /**
         * @param bool $value Whether to just immediately run updates in addUpdate()
         * @since 1.28
         */
        public static function setImmediateMode( $value ) {
                self::$immediateMode = (bool)$value;
        }

        /**
         * @param DeferrableUpdate[] $queue
         * @param DeferrableUpdate $update
         */
        private static function push( array &$queue, DeferrableUpdate $update ) {
                if ( $update instanceof MergeableUpdate ) {
                        $class = get_class( $update ); // fully-qualified class
                        if ( isset( $queue[$class] ) ) {
                                /** @var $existingUpdate MergeableUpdate */
                                $existingUpdate = $queue[$class];
                                $existingUpdate->merge( $update );
                        } else {
                                $queue[$class] = $update;
                        }
                } else {
                        $queue[] = $update;
                }
        }

        /**
         * Immediately run/queue a list of updates
         *
         * @param DeferrableUpdate[] &$queue List of DeferrableUpdate objects
         * @param string $mode Use "enqueue" to use the job queue when possible
         * @param integer $stage Class constant (PRESEND, POSTSEND) (since 1.28)
         * @throws ErrorPageError Happens on top-level calls
         * @throws Exception Happens on second-level calls
         */
        protected static function execute( array &$queue, $mode, $stage ) {
                $services = MediaWikiServices::getInstance();
                $stats = $services->getStatsdDataFactory();
                $lbFactory = $services->getDBLoadBalancerFactory();
                $method = RequestContext::getMain()->getRequest()->getMethod();

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

                /** @var ErrorPageError $reportableError */
                $reportableError = null;
                /** @var DeferrableUpdate[] $updates Snapshot of queue */
                $updates = $queue;

                // Keep doing rounds of updates until none get enqueued...
                while ( $updates ) {
                        $queue = []; // clear the queue

                        if ( $mode === 'enqueue' ) {
                                try {
                                        // Push enqueuable updates to the job queue and get the rest
                                        $updates = self::enqueueUpdates( $updates );
                                } catch ( Exception $e ) {
                                        // Let other updates have a chance to run if this failed
                                        MWExceptionHandler::rollbackMasterChangesAndLog( $e );
                                }
                        }

                        // Order will be DataUpdate followed by generic DeferrableUpdate tasks
                        $updatesByType = [ 'data' => [], 'generic' => [] ];
                        foreach ( $updates as $du ) {
                                if ( $du instanceof DataUpdate ) {
                                        $du->setTransactionTicket( $ticket );
                                        $updatesByType['data'][] = $du;
                                } else {
                                        $updatesByType['generic'][] = $du;
                                }

                                $name = ( $du instanceof DeferrableCallback )
                                        ? get_class( $du ) . '-' . $du->getOrigin()
                                        : get_class( $du );
                                $stats->increment( 'deferred_updates.' . $method . '.' . $name );
                        }

                        // Execute all remaining tasks...
                        foreach ( $updatesByType as $updatesForType ) {
                                foreach ( $updatesForType as $update ) {
                                        self::$executeContext = [
                                                'update' => $update,
                                                'stage' => $stage,
                                                'subqueue' => []
                                        ];
                                        /** @var DeferrableUpdate $update */
                                        $guiError = self::runUpdate( $update, $lbFactory, $stage );
                                        $reportableError = $reportableError ?: $guiError;
                                        // Do the subqueue updates for $update until there are none
                                        while ( self::$executeContext['subqueue'] ) {
                                                $subUpdate = reset( self::$executeContext['subqueue'] );
                                                $firstKey = key( self::$executeContext['subqueue'] );
                                                unset( self::$executeContext['subqueue'][$firstKey] );

                                                if ( $subUpdate instanceof DataUpdate ) {
                                                        $subUpdate->setTransactionTicket( $ticket );
                                                }

                                                $guiError = self::runUpdate( $subUpdate, $lbFactory, $stage );
                                                $reportableError = $reportableError ?: $guiError;
                                        }
                                        self::$executeContext = null;
                                }
                        }

                        $updates = $queue; // new snapshot of queue (check for new entries)
                }

                if ( $reportableError ) {
                        throw $reportableError; // throw the first of any GUI errors
                }
        }

        /**
         * @param DeferrableUpdate $update
         * @param LBFactory $lbFactory
         * @param integer $stage
         * @return ErrorPageError|null
         */
        private static function runUpdate( DeferrableUpdate $update, LBFactory $lbFactory, $stage ) {
                $guiError = null;
                try {
                        $fnameTrxOwner = get_class( $update ) . '::doUpdate';
                        $lbFactory->beginMasterChanges( $fnameTrxOwner );
                        $update->doUpdate();
                        $lbFactory->commitMasterChanges( $fnameTrxOwner );
                } catch ( Exception $e ) {
                        // Reporting GUI exceptions does not work post-send
                        if ( $e instanceof ErrorPageError && $stage === self::PRESEND ) {
                                $guiError = $e;
                        }
                        MWExceptionHandler::rollbackMasterChangesAndLog( $e );
                }

                return $guiError;
        }

        /**
         * Run all deferred updates immediately if there are no DB writes active
         *
         * If $mode is 'run' but there are busy databates, EnqueueableDataUpdate
         * tasks will be enqueued anyway for the sake of progress.
         *
         * @param string $mode Use "enqueue" to use the job queue when possible
         * @return bool Whether updates were allowed to run
         * @since 1.28
         */
        public static function tryOpportunisticExecute( $mode = 'run' ) {
                // execute() loop is already running
                if ( self::$executeContext ) {
                        return false;
                }

                // Avoiding running updates without them having outer scope
                if ( !self::getBusyDbConnections() ) {
                        self::doUpdates( $mode );
                        return true;
                }

                if ( self::pendingUpdatesCount() >= self::BIG_QUEUE_SIZE ) {
                        // If we cannot run the updates with outer transaction context, try to
                        // at least enqueue all the updates that support queueing to job queue
                        self::$preSendUpdates = self::enqueueUpdates( self::$preSendUpdates );
                        self::$postSendUpdates = self::enqueueUpdates( self::$postSendUpdates );
                }

                return !self::pendingUpdatesCount();
        }

        /**
         * Enqueue a job for each EnqueueableDataUpdate item and return the other items
         *
         * @param DeferrableUpdate[] $updates A list of deferred update instances
         * @return DeferrableUpdate[] Remaining updates that do not support being queued
         */
        private static function enqueueUpdates( array $updates ) {
                $remaining = [];

                foreach ( $updates as $update ) {
                        if ( $update instanceof EnqueueableDataUpdate ) {
                                $spec = $update->getAsJobSpecification();
                                JobQueueGroup::singleton( $spec['wiki'] )->push( $spec['job'] );
                        } else {
                                $remaining[] = $update;
                        }
                }

                return $remaining;
        }

        /**
         * @return integer Number of enqueued updates
         * @since 1.28
         */
        public static function pendingUpdatesCount() {
                return count( self::$preSendUpdates ) + count( self::$postSendUpdates );
        }

        /**
         * Clear all pending updates without performing them. Generally, you don't
         * want or need to call this. Unit tests need it though.
         */
        public static function clearPendingUpdates() {
                self::$preSendUpdates = [];
                self::$postSendUpdates = [];
        }

        /**
         * @return IDatabase[] Connection where commit() cannot be called yet
         */
        private static function getBusyDbConnections() {
                $connsBusy = [];

                $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
                $lbFactory->forEachLB( function ( LoadBalancer $lb ) use ( &$connsBusy ) {
                        $lb->forEachOpenMasterConnection( function ( IDatabase $conn ) use ( &$connsBusy ) {
                                if ( $conn->writesOrCallbacksPending() || $conn->explicitTrxActive() ) {
                                        $connsBusy[] = $conn;
                                }
                        } );
                } );

                return $connsBusy;
        }
}