JobRunner.php

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<?php
use MediaWiki\MediaWikiServices;
use MediaWiki\Logger\LoggerFactory;
use Liuggio\StatsdClient\Factory\StatsdDataFactory;
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Wikimedia\ScopedCallback;

class JobRunner implements LoggerAwareInterface {
    protected $debug;

    protected $logger;

    const MAX_ALLOWED_LAG = 3; // abort if more than this much DB lag is present
    const LAG_CHECK_PERIOD = 1.0; // check replica DB lag this many seconds
    const ERROR_BACKOFF_TTL = 1; // seconds to back off a queue due to errors

    public function setDebugHandler( $debug ) {
        $this->debug = $debug;
    }

    public function setLogger( LoggerInterface $logger ) {
        $this->logger = $logger;
    }

    public function __construct( LoggerInterface $logger = null ) {
        if ( $logger === null ) {
            $logger = LoggerFactory::getInstance( 'runJobs' );
        }
        $this->setLogger( $logger );
    }

    public function run( array $options ) {
        global $wgJobClasses, $wgTrxProfilerLimits;

        $response = [ 'jobs' => [], 'reached' => 'none-ready' ];

        $type = isset( $options['type'] ) ? $options['type'] : false;
        $maxJobs = isset( $options['maxJobs'] ) ? $options['maxJobs'] : false;
        $maxTime = isset( $options['maxTime'] ) ? $options['maxTime'] : false;
        $noThrottle = isset( $options['throttle'] ) && !$options['throttle'];

        // Bail if job type is invalid
        if ( $type !== false && !isset( $wgJobClasses[$type] ) ) {
            $response['reached'] = 'none-possible';
            return $response;
        }
        // Bail out if DB is in read-only mode
        if ( wfReadOnly() ) {
            $response['reached'] = 'read-only';
            return $response;
        }

        $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
        // Bail out if there is too much DB lag.
        // This check should not block as we want to try other wiki queues.
        list( , $maxLag ) = $lbFactory->getMainLB( wfWikiID() )->getMaxLag();
        if ( $maxLag >= self::MAX_ALLOWED_LAG ) {
            $response['reached'] = 'replica-lag-limit';
            return $response;
        }

        // Flush any pending DB writes for sanity
        $lbFactory->commitAll( __METHOD__ );

        // Catch huge single updates that lead to replica DB lag
        $trxProfiler = Profiler::instance()->getTransactionProfiler();
        $trxProfiler->setLogger( LoggerFactory::getInstance( 'DBPerformance' ) );
        $trxProfiler->setExpectations( $wgTrxProfilerLimits['JobRunner'], __METHOD__ );

        // Some jobs types should not run until a certain timestamp
        $backoffs = []; // map of (type => UNIX expiry)
        $backoffDeltas = []; // map of (type => seconds)
        $wait = 'wait'; // block to read backoffs the first time

        $group = JobQueueGroup::singleton();
        $stats = MediaWikiServices::getInstance()->getStatsdDataFactory();
        $jobsPopped = 0;
        $timeMsTotal = 0;
        $startTime = microtime( true ); // time since jobs started running
        $lastCheckTime = 1; // timestamp of last replica DB check
        do {
            // Sync the persistent backoffs with concurrent runners
            $backoffs = $this->syncBackoffDeltas( $backoffs, $backoffDeltas, $wait );
            $blacklist = $noThrottle ? [] : array_keys( $backoffs );
            $wait = 'nowait'; // less important now

            if ( $type === false ) {
                $job = $group->pop(
                    JobQueueGroup::TYPE_DEFAULT,
                    JobQueueGroup::USE_CACHE,
                    $blacklist
                );
            } elseif ( in_array( $type, $blacklist ) ) {
                $job = false; // requested queue in backoff state
            } else {
                $job = $group->pop( $type ); // job from a single queue
            }
            $lbFactory->commitMasterChanges( __METHOD__ ); // flush any JobQueueDB writes

            if ( $job ) { // found a job
                ++$jobsPopped;
                $popTime = time();
                $jType = $job->getType();

                WebRequest::overrideRequestId( $job->getRequestId() );

                // Back off of certain jobs for a while (for throttling and for errors)
                $ttw = $this->getBackoffTimeToWait( $job );
                if ( $ttw > 0 ) {
                    // Always add the delta for other runners in case the time running the
                    // job negated the backoff for each individually but not collectively.
                    $backoffDeltas[$jType] = isset( $backoffDeltas[$jType] )
                        ? $backoffDeltas[$jType] + $ttw
                        : $ttw;
                    $backoffs = $this->syncBackoffDeltas( $backoffs, $backoffDeltas, $wait );
                }

                $info = $this->executeJob( $job, $lbFactory, $stats, $popTime );
                if ( $info['status'] !== false || !$job->allowRetries() ) {
                    $group->ack( $job ); // succeeded or job cannot be retried
                    $lbFactory->commitMasterChanges( __METHOD__ ); // flush any JobQueueDB writes
                }

                // Back off of certain jobs for a while (for throttling and for errors)
                if ( $info['status'] === false && mt_rand( 0, 49 ) == 0 ) {
                    $ttw = max( $ttw, self::ERROR_BACKOFF_TTL ); // too many errors
                    $backoffDeltas[$jType] = isset( $backoffDeltas[$jType] )
                        ? $backoffDeltas[$jType] + $ttw
                        : $ttw;
                }

                $response['jobs'][] = [
                    'type'   => $jType,
                    'status' => ( $info['status'] === false ) ? 'failed' : 'ok',
                    'error'  => $info['error'],
                    'time'   => $info['timeMs']
                ];
                $timeMsTotal += $info['timeMs'];

                // Break out if we hit the job count or wall time limits...
                if ( $maxJobs && $jobsPopped >= $maxJobs ) {
                    $response['reached'] = 'job-limit';
                    break;
                } elseif ( $maxTime && ( microtime( true ) - $startTime ) > $maxTime ) {
                    $response['reached'] = 'time-limit';
                    break;
                }

                // Don't let any of the main DB replica DBs get backed up.
                // This only waits for so long before exiting and letting
                // other wikis in the farm (on different masters) get a chance.
                $timePassed = microtime( true ) - $lastCheckTime;
                if ( $timePassed >= self::LAG_CHECK_PERIOD || $timePassed < 0 ) {
                    try {
                        $lbFactory->waitForReplication( [
                            'ifWritesSince' => $lastCheckTime,
                            'timeout' => self::MAX_ALLOWED_LAG
                        ] );
                    } catch ( DBReplicationWaitError $e ) {
                        $response['reached'] = 'replica-lag-limit';
                        break;
                    }
                    $lastCheckTime = microtime( true );
                }
                // Don't let any queue replica DBs/backups fall behind
                if ( $jobsPopped > 0 && ( $jobsPopped % 100 ) == 0 ) {
                    $group->waitForBackups();
                }

                // Bail if near-OOM instead of in a job
                if ( !$this->checkMemoryOK() ) {
                    $response['reached'] = 'memory-limit';
                    break;
                }
            }
        } while ( $job ); // stop when there are no jobs

        // Sync the persistent backoffs for the next runJobs.php pass
        if ( $backoffDeltas ) {
            $this->syncBackoffDeltas( $backoffs, $backoffDeltas, 'wait' );
        }

        $response['backoffs'] = $backoffs;
        $response['elapsed'] = $timeMsTotal;

        return $response;
    }

    private function executeJob( Job $job, LBFactory $lbFactory, $stats, $popTime ) {
        $jType = $job->getType();
        $msg = $job->toString() . " STARTING";
        $this->logger->debug( $msg );
        $this->debugCallback( $msg );

        // Run the job...
        $rssStart = $this->getMaxRssKb();
        $jobStartTime = microtime( true );
        try {
            $fnameTrxOwner = get_class( $job ) . '::run'; // give run() outer scope
            $lbFactory->beginMasterChanges( $fnameTrxOwner );
            $status = $job->run();
            $error = $job->getLastError();
            $this->commitMasterChanges( $lbFactory, $job, $fnameTrxOwner );
            // Run any deferred update tasks; doUpdates() manages transactions itself
            DeferredUpdates::doUpdates();
        } catch ( Exception $e ) {
            MWExceptionHandler::rollbackMasterChangesAndLog( $e );
            $status = false;
            $error = get_class( $e ) . ': ' . $e->getMessage();
        }
        // Always attempt to call teardown() even if Job throws exception.
        try {
            $job->teardown( $status );
        } catch ( Exception $e ) {
            MWExceptionHandler::logException( $e );
        }

        // Commit all outstanding connections that are in a transaction
        // to get a fresh repeatable read snapshot on every connection.
        // Note that jobs are still responsible for handling replica DB lag.
        $lbFactory->flushReplicaSnapshots( __METHOD__ );
        // Clear out title cache data from prior snapshots
        MediaWikiServices::getInstance()->getLinkCache()->clear();
        $timeMs = intval( ( microtime( true ) - $jobStartTime ) * 1000 );
        $rssEnd = $this->getMaxRssKb();

        // Record how long jobs wait before getting popped
        $readyTs = $job->getReadyTimestamp();
        if ( $readyTs ) {
            $pickupDelay = max( 0, $popTime - $readyTs );
            $stats->timing( 'jobqueue.pickup_delay.all', 1000 * $pickupDelay );
            $stats->timing( "jobqueue.pickup_delay.$jType", 1000 * $pickupDelay );
        }
        // Record root job age for jobs being run
        $rootTimestamp = $job->getRootJobParams()['rootJobTimestamp'];
        if ( $rootTimestamp ) {
            $age = max( 0, $popTime - wfTimestamp( TS_UNIX, $rootTimestamp ) );
            $stats->timing( "jobqueue.pickup_root_age.$jType", 1000 * $age );
        }
        // Track the execution time for jobs
        $stats->timing( "jobqueue.run.$jType", $timeMs );
        // Track RSS increases for jobs (in case of memory leaks)
        if ( $rssStart && $rssEnd ) {
            $stats->updateCount( "jobqueue.rss_delta.$jType", $rssEnd - $rssStart );
        }

        if ( $status === false ) {
            $msg = $job->toString() . " t=$timeMs error={$error}";
            $this->logger->error( $msg );
            $this->debugCallback( $msg );
        } else {
            $msg = $job->toString() . " t=$timeMs good";
            $this->logger->info( $msg );
            $this->debugCallback( $msg );
        }

        return [ 'status' => $status, 'error' => $error, 'timeMs' => $timeMs ];
    }

    private function getMaxRssKb() {
        $info = wfGetRusage() ?: [];
        // see http://linux.die.net/man/2/getrusage
        return isset( $info['ru_maxrss'] ) ? (int)$info['ru_maxrss'] : null;
    }

    private function getBackoffTimeToWait( Job $job ) {
        global $wgJobBackoffThrottling;

        if ( !isset( $wgJobBackoffThrottling[$job->getType()] ) ||
            $job instanceof DuplicateJob // no work was done
        ) {
            return 0; // not throttled
        }

        $itemsPerSecond = $wgJobBackoffThrottling[$job->getType()];
        if ( $itemsPerSecond <= 0 ) {
            return 0; // not throttled
        }

        $seconds = 0;
        if ( $job->workItemCount() > 0 ) {
            $exactSeconds = $job->workItemCount() / $itemsPerSecond;
            // use randomized rounding
            $seconds = floor( $exactSeconds );
            $remainder = $exactSeconds - $seconds;
            $seconds += ( mt_rand() / mt_getrandmax() < $remainder ) ? 1 : 0;
        }

        return (int)$seconds;
    }

    private function loadBackoffs( array $backoffs, $mode = 'wait' ) {
        $file = wfTempDir() . '/mw-runJobs-backoffs.json';
        if ( is_file( $file ) ) {
            $noblock = ( $mode === 'nowait' ) ? LOCK_NB : 0;
            $handle = fopen( $file, 'rb' );
            if ( !flock( $handle, LOCK_SH | $noblock ) ) {
                fclose( $handle );
                return $backoffs; // don't wait on lock
            }
            $content = stream_get_contents( $handle );
            flock( $handle, LOCK_UN );
            fclose( $handle );
            $ctime = microtime( true );
            $cBackoffs = json_decode( $content, true ) ?: [];
            foreach ( $cBackoffs as $type => $timestamp ) {
                if ( $timestamp < $ctime ) {
                    unset( $cBackoffs[$type] );
                }
            }
        } else {
            $cBackoffs = [];
        }

        return $cBackoffs;
    }

    private function syncBackoffDeltas( array $backoffs, array &$deltas, $mode = 'wait' ) {
        if ( !$deltas ) {
            return $this->loadBackoffs( $backoffs, $mode );
        }

        $noblock = ( $mode === 'nowait' ) ? LOCK_NB : 0;
        $file = wfTempDir() . '/mw-runJobs-backoffs.json';
        $handle = fopen( $file, 'wb+' );
        if ( !flock( $handle, LOCK_EX | $noblock ) ) {
            fclose( $handle );
            return $backoffs; // don't wait on lock
        }
        $ctime = microtime( true );
        $content = stream_get_contents( $handle );
        $cBackoffs = json_decode( $content, true ) ?: [];
        foreach ( $deltas as $type => $seconds ) {
            $cBackoffs[$type] = isset( $cBackoffs[$type] ) && $cBackoffs[$type] >= $ctime
                ? $cBackoffs[$type] + $seconds
                : $ctime + $seconds;
        }
        foreach ( $cBackoffs as $type => $timestamp ) {
            if ( $timestamp < $ctime ) {
                unset( $cBackoffs[$type] );
            }
        }
        ftruncate( $handle, 0 );
        fwrite( $handle, json_encode( $cBackoffs ) );
        flock( $handle, LOCK_UN );
        fclose( $handle );

        $deltas = [];

        return $cBackoffs;
    }

    private function checkMemoryOK() {
        static $maxBytes = null;
        if ( $maxBytes === null ) {
            $m = [];
            if ( preg_match( '!^(\d+)(k|m|g|)$!i', ini_get( 'memory_limit' ), $m ) ) {
                list( , $num, $unit ) = $m;
                $conv = [ 'g' => 1073741824, 'm' => 1048576, 'k' => 1024, '' => 1 ];
                $maxBytes = $num * $conv[strtolower( $unit )];
            } else {
                $maxBytes = 0;
            }
        }
        $usedBytes = memory_get_usage();
        if ( $maxBytes && $usedBytes >= 0.95 * $maxBytes ) {
            $msg = "Detected excessive memory usage ($usedBytes/$maxBytes).";
            $this->debugCallback( $msg );
            $this->logger->error( $msg );

            return false;
        }

        return true;
    }

    private function debugCallback( $msg ) {
        if ( $this->debug ) {
            call_user_func_array( $this->debug, [ wfTimestamp( TS_DB ) . " $msg\n" ] );
        }
    }

    private function commitMasterChanges( LBFactory $lbFactory, Job $job, $fnameTrxOwner ) {
        global $wgJobSerialCommitThreshold;

        $time = false;
        $lb = $lbFactory->getMainLB( wfWikiID() );
        if ( $wgJobSerialCommitThreshold !== false && $lb->getServerCount() > 1 ) {
            // Generally, there is one master connection to the local DB
            $dbwSerial = $lb->getAnyOpenConnection( $lb->getWriterIndex() );
            // We need natively blocking fast locks
            if ( $dbwSerial && $dbwSerial->namedLocksEnqueue() ) {
                $time = $dbwSerial->pendingWriteQueryDuration( $dbwSerial::ESTIMATE_DB_APPLY );
                if ( $time < $wgJobSerialCommitThreshold ) {
                    $dbwSerial = false;
                }
            } else {
                $dbwSerial = false;
            }
        } else {
            // There are no replica DBs or writes are all to foreign DB (we don't handle that)
            $dbwSerial = false;
        }

        if ( !$dbwSerial ) {
            $lbFactory->commitMasterChanges( $fnameTrxOwner );
            return;
        }

        $ms = intval( 1000 * $time );
        $msg = $job->toString() . " COMMIT ENQUEUED [{$ms}ms of writes]";
        $this->logger->info( $msg );
        $this->debugCallback( $msg );

        // Wait for an exclusive lock to commit
        if ( !$dbwSerial->lock( 'jobrunner-serial-commit', __METHOD__, 30 ) ) {
            // This will trigger a rollback in the main loop
            throw new DBError( $dbwSerial, "Timed out waiting on commit queue." );
        }
        $unlocker = new ScopedCallback( function () use ( $dbwSerial ) {
            $dbwSerial->unlock( 'jobrunner-serial-commit', __METHOD__ );
        } );

        // Wait for the replica DBs to catch up
        $pos = $lb->getMasterPos();
        if ( $pos ) {
            $lb->waitForAll( $pos );
        }

        // Actually commit the DB master changes
        $lbFactory->commitMasterChanges( $fnameTrxOwner );
        ScopedCallback::consume( $unlocker );
    }
}