includes/jobqueue/JobRunner.php

   1 <?php
   2 /**
   3  * Job queue runner utility methods
   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  * @ingroup JobQueue
  22  */
  23
  24 use MediaWiki\MediaWikiServices;
  25 use MediaWiki\Logger\LoggerFactory;
  26 use Liuggio\StatsdClient\Factory\StatsdDataFactory;
  27 use Psr\Log\LoggerAwareInterface;
  28 use Psr\Log\LoggerInterface;
  29 use Wikimedia\ScopedCallback;
  30 use Wikimedia\Rdbms\LBFactory;
  31 use Wikimedia\Rdbms\DBError;
  32 use Wikimedia\Rdbms\DBReplicationWaitError;
  33
  34 /**
  35  * Job queue runner utility methods
  36  *
  37  * @ingroup JobQueue
  38  * @since 1.24
  39  */
  40 class JobRunner implements LoggerAwareInterface {
  41         /** @var Config */
  42         protected $config;
  43         /** @var callable|null Debug output handler */
  44         protected $debug;
  45
  46         /**
  47          * @var LoggerInterface $logger
  48          */
  49         protected $logger;
  50
  51         const MAX_ALLOWED_LAG = 3; // abort if more than this much DB lag is present
  52         const LAG_CHECK_PERIOD = 1.0; // check replica DB lag this many seconds
  53         const ERROR_BACKOFF_TTL = 1; // seconds to back off a queue due to errors
  54         const READONLY_BACKOFF_TTL = 30; // seconds to back off a queue due to read-only errors
  55
  56         /**
  57          * @param callable $debug Optional debug output handler
  58          */
  59         public function setDebugHandler( $debug ) {
  60                 $this->debug = $debug;
  61         }
  62
  63         /**
  64          * @param LoggerInterface $logger
  65          * @return void
  66          */
  67         public function setLogger( LoggerInterface $logger ) {
  68                 $this->logger = $logger;
  69         }
  70
  71         /**
  72          * @param LoggerInterface $logger
  73          */
  74         public function __construct( LoggerInterface $logger = null ) {
  75                 if ( $logger === null ) {
  76                         $logger = LoggerFactory::getInstance( 'runJobs' );
  77                 }
  78                 $this->setLogger( $logger );
  79                 $this->config = MediaWikiServices::getInstance()->getMainConfig();
  80         }
  81
  82         /**
  83          * Run jobs of the specified number/type for the specified time
  84          *
  85          * The response map has a 'job' field that lists status of each job, including:
  86          *   - type   : the job type
  87          *   - status : ok/failed
  88          *   - error  : any error message string
  89          *   - time   : the job run time in ms
  90          * The response map also has:
  91          *   - backoffs : the (job type => seconds) map of backoff times
  92          *   - elapsed  : the total time spent running tasks in ms
  93          *   - reached  : the reason the script finished, one of (none-ready, job-limit, time-limit,
  94          *  memory-limit)
  95          *
  96          * This method outputs status information only if a debug handler was set.
  97          * Any exceptions are caught and logged, but are not reported as output.
  98          *
  99          * @param array $options Map of parameters:
 100          *    - type     : the job type (or false for the default types)
 101          *    - maxJobs  : maximum number of jobs to run
 102          *    - maxTime  : maximum time in seconds before stopping
 103          *    - throttle : whether to respect job backoff configuration
 104          * @return array Summary response that can easily be JSON serialized
 105          */
 106         public function run( array $options ) {
 107                 $jobClasses = $this->config->get( 'JobClasses' );
 108                 $profilerLimits = $this->config->get( 'TrxProfilerLimits' );
 109
 110                 $response = [ 'jobs' => [], 'reached' => 'none-ready' ];
 111
 112                 $type = isset( $options['type'] ) ? $options['type'] : false;
 113                 $maxJobs = isset( $options['maxJobs'] ) ? $options['maxJobs'] : false;
 114                 $maxTime = isset( $options['maxTime'] ) ? $options['maxTime'] : false;
 115                 $noThrottle = isset( $options['throttle'] ) && !$options['throttle'];
 116
 117                 // Bail if job type is invalid
 118                 if ( $type !== false && !isset( $jobClasses[$type] ) ) {
 119                         $response['reached'] = 'none-possible';
 120                         return $response;
 121                 }
 122                 // Bail out if DB is in read-only mode
 123                 if ( wfReadOnly() ) {
 124                         $response['reached'] = 'read-only';
 125                         return $response;
 126                 }
 127
 128                 $lbFactory = MediaWikiServices::getInstance()->getDBLoadBalancerFactory();
 129                 // Bail out if there is too much DB lag.
 130                 // This check should not block as we want to try other wiki queues.
 131                 list( , $maxLag ) = $lbFactory->getMainLB( wfWikiID() )->getMaxLag();
 132                 if ( $maxLag >= self::MAX_ALLOWED_LAG ) {
 133                         $response['reached'] = 'replica-lag-limit';
 134                         return $response;
 135                 }
 136
 137                 // Flush any pending DB writes for sanity
 138                 $lbFactory->commitAll( __METHOD__ );
 139
 140                 // Catch huge single updates that lead to replica DB lag
 141                 $trxProfiler = Profiler::instance()->getTransactionProfiler();
 142                 $trxProfiler->setLogger( LoggerFactory::getInstance( 'DBPerformance' ) );
 143                 $trxProfiler->setExpectations( $profilerLimits['JobRunner'], __METHOD__ );
 144
 145                 // Some jobs types should not run until a certain timestamp
 146                 $backoffs = []; // map of (type => UNIX expiry)
 147                 $backoffDeltas = []; // map of (type => seconds)
 148                 $wait = 'wait'; // block to read backoffs the first time
 149
 150                 $group = JobQueueGroup::singleton();
 151                 $stats = MediaWikiServices::getInstance()->getStatsdDataFactory();
 152                 $jobsPopped = 0;
 153                 $timeMsTotal = 0;
 154                 $startTime = microtime( true ); // time since jobs started running
 155                 $lastCheckTime = 1; // timestamp of last replica DB check
 156                 do {
 157                         // Sync the persistent backoffs with concurrent runners
 158                         $backoffs = $this->syncBackoffDeltas( $backoffs, $backoffDeltas, $wait );
 159                         $blacklist = $noThrottle ? [] : array_keys( $backoffs );
 160                         $wait = 'nowait'; // less important now
 161
 162                         if ( $type === false ) {
 163                                 $job = $group->pop(
 164                                         JobQueueGroup::TYPE_DEFAULT,
 165                                         JobQueueGroup::USE_CACHE,
 166                                         $blacklist
 167                                 );
 168                         } elseif ( in_array( $type, $blacklist ) ) {
 169                                 $job = false; // requested queue in backoff state
 170                         } else {
 171                                 $job = $group->pop( $type ); // job from a single queue
 172                         }
 173                         $lbFactory->commitMasterChanges( __METHOD__ ); // flush any JobQueueDB writes
 174
 175                         if ( $job ) { // found a job
 176                                 ++$jobsPopped;
 177                                 $popTime = time();
 178                                 $jType = $job->getType();
 179
 180                                 WebRequest::overrideRequestId( $job->getRequestId() );
 181
 182                                 // Back off of certain jobs for a while (for throttling and for errors)
 183                                 $ttw = $this->getBackoffTimeToWait( $job );
 184                                 if ( $ttw > 0 ) {
 185                                         // Always add the delta for other runners in case the time running the
 186                                         // job negated the backoff for each individually but not collectively.
 187                                         $backoffDeltas[$jType] = isset( $backoffDeltas[$jType] )
 188                                                 ? $backoffDeltas[$jType] + $ttw
 189                                                 : $ttw;
 190                                         $backoffs = $this->syncBackoffDeltas( $backoffs, $backoffDeltas, $wait );
 191                                 }
 192
 193                                 $info = $this->executeJob( $job, $lbFactory, $stats, $popTime );
 194                                 if ( $info['status'] !== false || !$job->allowRetries() ) {
 195                                         $group->ack( $job ); // succeeded or job cannot be retried
 196                                         $lbFactory->commitMasterChanges( __METHOD__ ); // flush any JobQueueDB writes
 197                                 }
 198
 199                                 // Back off of certain jobs for a while (for throttling and for errors)
 200                                 if ( $info['status'] === false && mt_rand( 0, 49 ) == 0 ) {
 201                                         $ttw = max( $ttw, $this->getErrorBackoffTTL( $info['error'] ) );
 202                                         $backoffDeltas[$jType] = isset( $backoffDeltas[$jType] )
 203                                                 ? $backoffDeltas[$jType] + $ttw
 204                                                 : $ttw;
 205                                 }
 206
 207                                 $response['jobs'][] = [
 208                                         'type'   => $jType,
 209                                         'status' => ( $info['status'] === false ) ? 'failed' : 'ok',
 210                                         'error'  => $info['error'],
 211                                         'time'   => $info['timeMs']
 212                                 ];
 213                                 $timeMsTotal += $info['timeMs'];
 214
 215                                 // Break out if we hit the job count or wall time limits...
 216                                 if ( $maxJobs && $jobsPopped >= $maxJobs ) {
 217                                         $response['reached'] = 'job-limit';
 218                                         break;
 219                                 } elseif ( $maxTime && ( microtime( true ) - $startTime ) > $maxTime ) {
 220                                         $response['reached'] = 'time-limit';
 221                                         break;
 222                                 }
 223
 224                                 // Don't let any of the main DB replica DBs get backed up.
 225                                 // This only waits for so long before exiting and letting
 226                                 // other wikis in the farm (on different masters) get a chance.
 227                                 $timePassed = microtime( true ) - $lastCheckTime;
 228                                 if ( $timePassed >= self::LAG_CHECK_PERIOD || $timePassed < 0 ) {
 229                                         try {
 230                                                 $lbFactory->waitForReplication( [
 231                                                         'ifWritesSince' => $lastCheckTime,
 232                                                         'timeout' => self::MAX_ALLOWED_LAG
 233                                                 ] );
 234                                         } catch ( DBReplicationWaitError $e ) {
 235                                                 $response['reached'] = 'replica-lag-limit';
 236                                                 break;
 237                                         }
 238                                         $lastCheckTime = microtime( true );
 239                                 }
 240                                 // Don't let any queue replica DBs/backups fall behind
 241                                 if ( $jobsPopped > 0 && ( $jobsPopped % 100 ) == 0 ) {
 242                                         $group->waitForBackups();
 243                                 }
 244
 245                                 // Bail if near-OOM instead of in a job
 246                                 if ( !$this->checkMemoryOK() ) {
 247                                         $response['reached'] = 'memory-limit';
 248                                         break;
 249                                 }
 250                         }
 251                 } while ( $job ); // stop when there are no jobs
 252
 253                 // Sync the persistent backoffs for the next runJobs.php pass
 254                 if ( $backoffDeltas ) {
 255                         $this->syncBackoffDeltas( $backoffs, $backoffDeltas, 'wait' );
 256                 }
 257
 258                 $response['backoffs'] = $backoffs;
 259                 $response['elapsed'] = $timeMsTotal;
 260
 261                 return $response;
 262         }
 263
 264         /**
 265          * @param string $error
 266          * @return int TTL in seconds
 267          */
 268         private function getErrorBackoffTTL( $error ) {
 269                 return strpos( $error, 'DBReadOnlyError' ) !== false
 270                         ? self::READONLY_BACKOFF_TTL
 271                         : self::ERROR_BACKOFF_TTL;
 272         }
 273
 274         /**
 275          * @param Job $job
 276          * @param LBFactory $lbFactory
 277          * @param StatsdDataFactory $stats
 278          * @param float $popTime
 279          * @return array Map of status/error/timeMs
 280          */
 281         private function executeJob( Job $job, LBFactory $lbFactory, $stats, $popTime ) {
 282                 $jType = $job->getType();
 283                 $msg = $job->toString() . " STARTING";
 284                 $this->logger->debug( $msg );
 285                 $this->debugCallback( $msg );
 286
 287                 // Run the job...
 288                 $rssStart = $this->getMaxRssKb();
 289                 $jobStartTime = microtime( true );
 290                 try {
 291                         $fnameTrxOwner = get_class( $job ) . '::run'; // give run() outer scope
 292                         $lbFactory->beginMasterChanges( $fnameTrxOwner );
 293                         $status = $job->run();
 294                         $error = $job->getLastError();
 295                         $this->commitMasterChanges( $lbFactory, $job, $fnameTrxOwner );
 296                         // Important: this must be the last deferred update added (T100085, T154425)
 297                         DeferredUpdates::addCallableUpdate( [ JobQueueGroup::class, 'pushLazyJobs' ] );
 298                         // Run any deferred update tasks; doUpdates() manages transactions itself
 299                         DeferredUpdates::doUpdates();
 300                 } catch ( Exception $e ) {
 301                         MWExceptionHandler::rollbackMasterChangesAndLog( $e );
 302                         $status = false;
 303                         $error = get_class( $e ) . ': ' . $e->getMessage();
 304                 }
 305                 // Always attempt to call teardown() even if Job throws exception.
 306                 try {
 307                         $job->teardown( $status );
 308                 } catch ( Exception $e ) {
 309                         MWExceptionHandler::logException( $e );
 310                 }
 311
 312                 // Commit all outstanding connections that are in a transaction
 313                 // to get a fresh repeatable read snapshot on every connection.
 314                 // Note that jobs are still responsible for handling replica DB lag.
 315                 $lbFactory->flushReplicaSnapshots( __METHOD__ );
 316                 // Clear out title cache data from prior snapshots
 317                 MediaWikiServices::getInstance()->getLinkCache()->clear();
 318                 $timeMs = intval( ( microtime( true ) - $jobStartTime ) * 1000 );
 319                 $rssEnd = $this->getMaxRssKb();
 320
 321                 // Record how long jobs wait before getting popped
 322                 $readyTs = $job->getReadyTimestamp();
 323                 if ( $readyTs ) {
 324                         $pickupDelay = max( 0, $popTime - $readyTs );
 325                         $stats->timing( 'jobqueue.pickup_delay.all', 1000 * $pickupDelay );
 326                         $stats->timing( "jobqueue.pickup_delay.$jType", 1000 * $pickupDelay );
 327                 }
 328                 // Record root job age for jobs being run
 329                 $rootTimestamp = $job->getRootJobParams()['rootJobTimestamp'];
 330                 if ( $rootTimestamp ) {
 331                         $age = max( 0, $popTime - wfTimestamp( TS_UNIX, $rootTimestamp ) );
 332                         $stats->timing( "jobqueue.pickup_root_age.$jType", 1000 * $age );
 333                 }
 334                 // Track the execution time for jobs
 335                 $stats->timing( "jobqueue.run.$jType", $timeMs );
 336                 // Track RSS increases for jobs (in case of memory leaks)
 337                 if ( $rssStart && $rssEnd ) {
 338                         $stats->updateCount( "jobqueue.rss_delta.$jType", $rssEnd - $rssStart );
 339                 }
 340
 341                 if ( $status === false ) {
 342                         $msg = $job->toString() . " t=$timeMs error={$error}";
 343                         $this->logger->error( $msg );
 344                         $this->debugCallback( $msg );
 345                 } else {
 346                         $msg = $job->toString() . " t=$timeMs good";
 347                         $this->logger->info( $msg );
 348                         $this->debugCallback( $msg );
 349                 }
 350
 351                 return [ 'status' => $status, 'error' => $error, 'timeMs' => $timeMs ];
 352         }
 353
 354         /**
 355          * @return int|null Max memory RSS in kilobytes
 356          */
 357         private function getMaxRssKb() {
 358                 $info = wfGetRusage() ?: [];
 359                 // see https://linux.die.net/man/2/getrusage
 360                 return isset( $info['ru_maxrss'] ) ? (int)$info['ru_maxrss'] : null;
 361         }
 362
 363         /**
 364          * @param Job $job
 365          * @return int Seconds for this runner to avoid doing more jobs of this type
 366          * @see $wgJobBackoffThrottling
 367          */
 368         private function getBackoffTimeToWait( Job $job ) {
 369                 $throttling = $this->config->get( 'JobBackoffThrottling' );
 370
 371                 if ( !isset( $throttling[$job->getType()] ) || $job instanceof DuplicateJob ) {
 372                         return 0; // not throttled
 373                 }
 374
 375                 $itemsPerSecond = $throttling[$job->getType()];
 376                 if ( $itemsPerSecond <= 0 ) {
 377                         return 0; // not throttled
 378                 }
 379
 380                 $seconds = 0;
 381                 if ( $job->workItemCount() > 0 ) {
 382                         $exactSeconds = $job->workItemCount() / $itemsPerSecond;
 383                         // use randomized rounding
 384                         $seconds = floor( $exactSeconds );
 385                         $remainder = $exactSeconds - $seconds;
 386                         $seconds += ( mt_rand() / mt_getrandmax() < $remainder ) ? 1 : 0;
 387                 }
 388
 389                 return (int)$seconds;
 390         }
 391
 392         /**
 393          * Get the previous backoff expiries from persistent storage
 394          * On I/O or lock acquisition failure this returns the original $backoffs.
 395          *
 396          * @param array $backoffs Map of (job type => UNIX timestamp)
 397          * @param string $mode Lock wait mode - "wait" or "nowait"
 398          * @return array Map of (job type => backoff expiry timestamp)
 399          */
 400         private function loadBackoffs( array $backoffs, $mode = 'wait' ) {
 401                 $file = wfTempDir() . '/mw-runJobs-backoffs.json';
 402                 if ( is_file( $file ) ) {
 403                         $noblock = ( $mode === 'nowait' ) ? LOCK_NB : 0;
 404                         $handle = fopen( $file, 'rb' );
 405                         if ( !flock( $handle, LOCK_SH | $noblock ) ) {
 406                                 fclose( $handle );
 407                                 return $backoffs; // don't wait on lock
 408                         }
 409                         $content = stream_get_contents( $handle );
 410                         flock( $handle, LOCK_UN );
 411                         fclose( $handle );
 412                         $ctime = microtime( true );
 413                         $cBackoffs = json_decode( $content, true ) ?: [];
 414                         foreach ( $cBackoffs as $type => $timestamp ) {
 415                                 if ( $timestamp < $ctime ) {
 416                                         unset( $cBackoffs[$type] );
 417                                 }
 418                         }
 419                 } else {
 420                         $cBackoffs = [];
 421                 }
 422
 423                 return $cBackoffs;
 424         }
 425
 426         /**
 427          * Merge the current backoff expiries from persistent storage
 428          *
 429          * The $deltas map is set to an empty array on success.
 430          * On I/O or lock acquisition failure this returns the original $backoffs.
 431          *
 432          * @param array $backoffs Map of (job type => UNIX timestamp)
 433          * @param array $deltas Map of (job type => seconds)
 434          * @param string $mode Lock wait mode - "wait" or "nowait"
 435          * @return array The new backoffs account for $backoffs and the latest file data
 436          */
 437         private function syncBackoffDeltas( array $backoffs, array &$deltas, $mode = 'wait' ) {
 438                 if ( !$deltas ) {
 439                         return $this->loadBackoffs( $backoffs, $mode );
 440                 }
 441
 442                 $noblock = ( $mode === 'nowait' ) ? LOCK_NB : 0;
 443                 $file = wfTempDir() . '/mw-runJobs-backoffs.json';
 444                 $handle = fopen( $file, 'wb+' );
 445                 if ( !flock( $handle, LOCK_EX | $noblock ) ) {
 446                         fclose( $handle );
 447                         return $backoffs; // don't wait on lock
 448                 }
 449                 $ctime = microtime( true );
 450                 $content = stream_get_contents( $handle );
 451                 $cBackoffs = json_decode( $content, true ) ?: [];
 452                 foreach ( $deltas as $type => $seconds ) {
 453                         $cBackoffs[$type] = isset( $cBackoffs[$type] ) && $cBackoffs[$type] >= $ctime
 454                                 ? $cBackoffs[$type] + $seconds
 455                                 : $ctime + $seconds;
 456                 }
 457                 foreach ( $cBackoffs as $type => $timestamp ) {
 458                         if ( $timestamp < $ctime ) {
 459                                 unset( $cBackoffs[$type] );
 460                         }
 461                 }
 462                 ftruncate( $handle, 0 );
 463                 fwrite( $handle, json_encode( $cBackoffs ) );
 464                 flock( $handle, LOCK_UN );
 465                 fclose( $handle );
 466
 467                 $deltas = [];
 468
 469                 return $cBackoffs;
 470         }
 471
 472         /**
 473          * Make sure that this script is not too close to the memory usage limit.
 474          * It is better to die in between jobs than OOM right in the middle of one.
 475          * @return bool
 476          */
 477         private function checkMemoryOK() {
 478                 static $maxBytes = null;
 479                 if ( $maxBytes === null ) {
 480                         $m = [];
 481                         if ( preg_match( '!^(\d+)(k|m|g|)$!i', ini_get( 'memory_limit' ), $m ) ) {
 482                                 list( , $num, $unit ) = $m;
 483                                 $conv = [ 'g' => 1073741824, 'm' => 1048576, 'k' => 1024, '' => 1 ];
 484                                 $maxBytes = $num * $conv[strtolower( $unit )];
 485                         } else {
 486                                 $maxBytes = 0;
 487                         }
 488                 }
 489                 $usedBytes = memory_get_usage();
 490                 if ( $maxBytes && $usedBytes >= 0.95 * $maxBytes ) {
 491                         $msg = "Detected excessive memory usage ($usedBytes/$maxBytes).";
 492                         $this->debugCallback( $msg );
 493                         $this->logger->error( $msg );
 494
 495                         return false;
 496                 }
 497
 498                 return true;
 499         }
 500
 501         /**
 502          * Log the job message
 503          * @param string $msg The message to log
 504          */
 505         private function debugCallback( $msg ) {
 506                 if ( $this->debug ) {
 507                         call_user_func_array( $this->debug, [ wfTimestamp( TS_DB ) . " $msg\n" ] );
 508                 }
 509         }
 510
 511         /**
 512          * Issue a commit on all masters who are currently in a transaction and have
 513          * made changes to the database. It also supports sometimes waiting for the
 514          * local wiki's replica DBs to catch up. See the documentation for
 515          * $wgJobSerialCommitThreshold for more.
 516          *
 517          * @param LBFactory $lbFactory
 518          * @param Job $job
 519          * @param string $fnameTrxOwner
 520          * @throws DBError
 521          */
 522         private function commitMasterChanges( LBFactory $lbFactory, Job $job, $fnameTrxOwner ) {
 523                 $syncThreshold = $this->config->get( 'JobSerialCommitThreshold' );
 524
 525                 $time = false;
 526                 $lb = $lbFactory->getMainLB( wfWikiID() );
 527                 if ( $syncThreshold !== false && $lb->getServerCount() > 1 ) {
 528                         // Generally, there is one master connection to the local DB
 529                         $dbwSerial = $lb->getAnyOpenConnection( $lb->getWriterIndex() );
 530                         // We need natively blocking fast locks
 531                         if ( $dbwSerial && $dbwSerial->namedLocksEnqueue() ) {
 532                                 $time = $dbwSerial->pendingWriteQueryDuration( $dbwSerial::ESTIMATE_DB_APPLY );
 533                                 if ( $time < $syncThreshold ) {
 534                                         $dbwSerial = false;
 535                                 }
 536                         } else {
 537                                 $dbwSerial = false;
 538                         }
 539                 } else {
 540                         // There are no replica DBs or writes are all to foreign DB (we don't handle that)
 541                         $dbwSerial = false;
 542                 }
 543
 544                 if ( !$dbwSerial ) {
 545                         $lbFactory->commitMasterChanges(
 546                                 $fnameTrxOwner,
 547                                 // Abort if any transaction was too big
 548                                 [ 'maxWriteDuration' => $this->config->get( 'MaxJobDBWriteDuration' ) ]
 549                         );
 550
 551                         return;
 552                 }
 553
 554                 $ms = intval( 1000 * $time );
 555                 $msg = $job->toString() . " COMMIT ENQUEUED [{$ms}ms of writes]";
 556                 $this->logger->info( $msg );
 557                 $this->debugCallback( $msg );
 558
 559                 // Wait for an exclusive lock to commit
 560                 if ( !$dbwSerial->lock( 'jobrunner-serial-commit', __METHOD__, 30 ) ) {
 561                         // This will trigger a rollback in the main loop
 562                         throw new DBError( $dbwSerial, "Timed out waiting on commit queue." );
 563                 }
 564                 $unlocker = new ScopedCallback( function () use ( $dbwSerial ) {
 565                         $dbwSerial->unlock( 'jobrunner-serial-commit', __METHOD__ );
 566                 } );
 567
 568                 // Wait for the replica DBs to catch up
 569                 $pos = $lb->getMasterPos();
 570                 if ( $pos ) {
 571                         $lb->waitForAll( $pos );
 572                 }
 573
 574                 // Actually commit the DB master changes
 575                 $lbFactory->commitMasterChanges(
 576                         $fnameTrxOwner,
 577                         // Abort if any transaction was too big
 578                         [ 'maxWriteDuration' => $this->config->get( 'MaxJobDBWriteDuration' ) ]
 579                 );
 580                 ScopedCallback::consume( $unlocker );
 581         }
 582 }