includes/jobqueue/JobQueue.php

   1 <?php
   2 /**
   3  * Job queue base code.
   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  * @defgroup JobQueue JobQueue
  22  * @author Aaron Schulz
  23  */
  24 use MediaWiki\MediaWikiServices;
  25
  26 /**
  27  * Class to handle enqueueing and running of background jobs
  28  *
  29  * @ingroup JobQueue
  30  * @since 1.21
  31  */
  32 abstract class JobQueue {
  33         /** @var string Wiki ID */
  34         protected $wiki;
  35         /** @var string Job type */
  36         protected $type;
  37         /** @var string Job priority for pop() */
  38         protected $order;
  39         /** @var int Time to live in seconds */
  40         protected $claimTTL;
  41         /** @var int Maximum number of times to try a job */
  42         protected $maxTries;
  43         /** @var string|bool Read only rationale (or false if r/w) */
  44         protected $readOnlyReason;
  45
  46         /** @var BagOStuff */
  47         protected $dupCache;
  48         /** @var JobQueueAggregator */
  49         protected $aggr;
  50
  51         const QOS_ATOMIC = 1; // integer; "all-or-nothing" job insertions
  52
  53         const ROOTJOB_TTL = 2419200; // integer; seconds to remember root jobs (28 days)
  54
  55         /**
  56          * @param array $params
  57          * @throws MWException
  58          */
  59         protected function __construct( array $params ) {
  60                 $this->wiki = $params['wiki'];
  61                 $this->type = $params['type'];
  62                 $this->claimTTL = isset( $params['claimTTL'] ) ? $params['claimTTL'] : 0;
  63                 $this->maxTries = isset( $params['maxTries'] ) ? $params['maxTries'] : 3;
  64                 if ( isset( $params['order'] ) && $params['order'] !== 'any' ) {
  65                         $this->order = $params['order'];
  66                 } else {
  67                         $this->order = $this->optimalOrder();
  68                 }
  69                 if ( !in_array( $this->order, $this->supportedOrders() ) ) {
  70                         throw new MWException( __CLASS__ . " does not support '{$this->order}' order." );
  71                 }
  72                 $this->dupCache = wfGetCache( CACHE_ANYTHING );
  73                 $this->aggr = isset( $params['aggregator'] )
  74                         ? $params['aggregator']
  75                         : new JobQueueAggregatorNull( [] );
  76                 $this->readOnlyReason = isset( $params['readOnlyReason'] )
  77                         ? $params['readOnlyReason']
  78                         : false;
  79         }
  80
  81         /**
  82          * Get a job queue object of the specified type.
  83          * $params includes:
  84          *   - class      : What job class to use (determines job type)
  85          *   - wiki       : wiki ID of the wiki the jobs are for (defaults to current wiki)
  86          *   - type       : The name of the job types this queue handles
  87          *   - order      : Order that pop() selects jobs, one of "fifo", "timestamp" or "random".
  88          *                  If "fifo" is used, the queue will effectively be FIFO. Note that job
  89          *                  completion will not appear to be exactly FIFO if there are multiple
  90          *                  job runners since jobs can take different times to finish once popped.
  91          *                  If "timestamp" is used, the queue will at least be loosely ordered
  92          *                  by timestamp, allowing for some jobs to be popped off out of order.
  93          *                  If "random" is used, pop() will pick jobs in random order.
  94          *                  Note that it may only be weakly random (e.g. a lottery of the oldest X).
  95          *                  If "any" is choosen, the queue will use whatever order is the fastest.
  96          *                  This might be useful for improving concurrency for job acquisition.
  97          *   - claimTTL   : If supported, the queue will recycle jobs that have been popped
  98          *                  but not acknowledged as completed after this many seconds. Recycling
  99          *                  of jobs simply means re-inserting them into the queue. Jobs can be
 100          *                  attempted up to three times before being discarded.
 101          *   - readOnlyReason : Set this to a string to make the queue read-only.
 102          *
 103          * Queue classes should throw an exception if they do not support the options given.
 104          *
 105          * @param array $params
 106          * @return JobQueue
 107          * @throws MWException
 108          */
 109         final public static function factory( array $params ) {
 110                 $class = $params['class'];
 111                 if ( !class_exists( $class ) ) {
 112                         throw new MWException( "Invalid job queue class '$class'." );
 113                 }
 114                 $obj = new $class( $params );
 115                 if ( !( $obj instanceof self ) ) {
 116                         throw new MWException( "Class '$class' is not a " . __CLASS__ . " class." );
 117                 }
 118
 119                 return $obj;
 120         }
 121
 122         /**
 123          * @return string Wiki ID
 124          */
 125         final public function getWiki() {
 126                 return $this->wiki;
 127         }
 128
 129         /**
 130          * @return string Job type that this queue handles
 131          */
 132         final public function getType() {
 133                 return $this->type;
 134         }
 135
 136         /**
 137          * @return string One of (random, timestamp, fifo, undefined)
 138          */
 139         final public function getOrder() {
 140                 return $this->order;
 141         }
 142
 143         /**
 144          * Get the allowed queue orders for configuration validation
 145          *
 146          * @return array Subset of (random, timestamp, fifo, undefined)
 147          */
 148         abstract protected function supportedOrders();
 149
 150         /**
 151          * Get the default queue order to use if configuration does not specify one
 152          *
 153          * @return string One of (random, timestamp, fifo, undefined)
 154          */
 155         abstract protected function optimalOrder();
 156
 157         /**
 158          * Find out if delayed jobs are supported for configuration validation
 159          *
 160          * @return bool Whether delayed jobs are supported
 161          */
 162         protected function supportsDelayedJobs() {
 163                 return false; // not implemented
 164         }
 165
 166         /**
 167          * @return bool Whether delayed jobs are enabled
 168          * @since 1.22
 169          */
 170         final public function delayedJobsEnabled() {
 171                 return $this->supportsDelayedJobs();
 172         }
 173
 174         /**
 175          * @return string|bool Read-only rational or false if r/w
 176          * @since 1.27
 177          */
 178         public function getReadOnlyReason() {
 179                 return $this->readOnlyReason;
 180         }
 181
 182         /**
 183          * Quickly check if the queue has no available (unacquired, non-delayed) jobs.
 184          * Queue classes should use caching if they are any slower without memcached.
 185          *
 186          * If caching is used, this might return false when there are actually no jobs.
 187          * If pop() is called and returns false then it should correct the cache. Also,
 188          * calling flushCaches() first prevents this. However, this affect is typically
 189          * not distinguishable from the race condition between isEmpty() and pop().
 190          *
 191          * @return bool
 192          * @throws JobQueueError
 193          */
 194         final public function isEmpty() {
 195                 $res = $this->doIsEmpty();
 196
 197                 return $res;
 198         }
 199
 200         /**
 201          * @see JobQueue::isEmpty()
 202          * @return bool
 203          */
 204         abstract protected function doIsEmpty();
 205
 206         /**
 207          * Get the number of available (unacquired, non-delayed) jobs in the queue.
 208          * Queue classes should use caching if they are any slower without memcached.
 209          *
 210          * If caching is used, this number might be out of date for a minute.
 211          *
 212          * @return int
 213          * @throws JobQueueError
 214          */
 215         final public function getSize() {
 216                 $res = $this->doGetSize();
 217
 218                 return $res;
 219         }
 220
 221         /**
 222          * @see JobQueue::getSize()
 223          * @return int
 224          */
 225         abstract protected function doGetSize();
 226
 227         /**
 228          * Get the number of acquired jobs (these are temporarily out of the queue).
 229          * Queue classes should use caching if they are any slower without memcached.
 230          *
 231          * If caching is used, this number might be out of date for a minute.
 232          *
 233          * @return int
 234          * @throws JobQueueError
 235          */
 236         final public function getAcquiredCount() {
 237                 $res = $this->doGetAcquiredCount();
 238
 239                 return $res;
 240         }
 241
 242         /**
 243          * @see JobQueue::getAcquiredCount()
 244          * @return int
 245          */
 246         abstract protected function doGetAcquiredCount();
 247
 248         /**
 249          * Get the number of delayed jobs (these are temporarily out of the queue).
 250          * Queue classes should use caching if they are any slower without memcached.
 251          *
 252          * If caching is used, this number might be out of date for a minute.
 253          *
 254          * @return int
 255          * @throws JobQueueError
 256          * @since 1.22
 257          */
 258         final public function getDelayedCount() {
 259                 $res = $this->doGetDelayedCount();
 260
 261                 return $res;
 262         }
 263
 264         /**
 265          * @see JobQueue::getDelayedCount()
 266          * @return int
 267          */
 268         protected function doGetDelayedCount() {
 269                 return 0; // not implemented
 270         }
 271
 272         /**
 273          * Get the number of acquired jobs that can no longer be attempted.
 274          * Queue classes should use caching if they are any slower without memcached.
 275          *
 276          * If caching is used, this number might be out of date for a minute.
 277          *
 278          * @return int
 279          * @throws JobQueueError
 280          */
 281         final public function getAbandonedCount() {
 282                 $res = $this->doGetAbandonedCount();
 283
 284                 return $res;
 285         }
 286
 287         /**
 288          * @see JobQueue::getAbandonedCount()
 289          * @return int
 290          */
 291         protected function doGetAbandonedCount() {
 292                 return 0; // not implemented
 293         }
 294
 295         /**
 296          * Push one or more jobs into the queue.
 297          * This does not require $wgJobClasses to be set for the given job type.
 298          * Outside callers should use JobQueueGroup::push() instead of this function.
 299          *
 300          * @param IJobSpecification|IJobSpecification[] $jobs
 301          * @param int $flags Bitfield (supports JobQueue::QOS_ATOMIC)
 302          * @return void
 303          * @throws JobQueueError
 304          */
 305         final public function push( $jobs, $flags = 0 ) {
 306                 $jobs = is_array( $jobs ) ? $jobs : [ $jobs ];
 307                 $this->batchPush( $jobs, $flags );
 308         }
 309
 310         /**
 311          * Push a batch of jobs into the queue.
 312          * This does not require $wgJobClasses to be set for the given job type.
 313          * Outside callers should use JobQueueGroup::push() instead of this function.
 314          *
 315          * @param IJobSpecification[] $jobs
 316          * @param int $flags Bitfield (supports JobQueue::QOS_ATOMIC)
 317          * @return void
 318          * @throws MWException
 319          */
 320         final public function batchPush( array $jobs, $flags = 0 ) {
 321                 $this->assertNotReadOnly();
 322
 323                 if ( !count( $jobs ) ) {
 324                         return; // nothing to do
 325                 }
 326
 327                 foreach ( $jobs as $job ) {
 328                         if ( $job->getType() !== $this->type ) {
 329                                 throw new MWException(
 330                                         "Got '{$job->getType()}' job; expected a '{$this->type}' job." );
 331                         } elseif ( $job->getReleaseTimestamp() && !$this->supportsDelayedJobs() ) {
 332                                 throw new MWException(
 333                                         "Got delayed '{$job->getType()}' job; delays are not supported." );
 334                         }
 335                 }
 336
 337                 $this->doBatchPush( $jobs, $flags );
 338                 $this->aggr->notifyQueueNonEmpty( $this->wiki, $this->type );
 339
 340                 foreach ( $jobs as $job ) {
 341                         if ( $job->isRootJob() ) {
 342                                 $this->deduplicateRootJob( $job );
 343                         }
 344                 }
 345         }
 346
 347         /**
 348          * @see JobQueue::batchPush()
 349          * @param IJobSpecification[] $jobs
 350          * @param int $flags
 351          */
 352         abstract protected function doBatchPush( array $jobs, $flags );
 353
 354         /**
 355          * Pop a job off of the queue.
 356          * This requires $wgJobClasses to be set for the given job type.
 357          * Outside callers should use JobQueueGroup::pop() instead of this function.
 358          *
 359          * @throws MWException
 360          * @return Job|bool Returns false if there are no jobs
 361          */
 362         final public function pop() {
 363                 global $wgJobClasses;
 364
 365                 $this->assertNotReadOnly();
 366                 if ( $this->wiki !== wfWikiID() ) {
 367                         throw new MWException( "Cannot pop '{$this->type}' job off foreign wiki queue." );
 368                 } elseif ( !isset( $wgJobClasses[$this->type] ) ) {
 369                         // Do not pop jobs if there is no class for the queue type
 370                         throw new MWException( "Unrecognized job type '{$this->type}'." );
 371                 }
 372
 373                 $job = $this->doPop();
 374
 375                 if ( !$job ) {
 376                         $this->aggr->notifyQueueEmpty( $this->wiki, $this->type );
 377                 }
 378
 379                 // Flag this job as an old duplicate based on its "root" job...
 380                 try {
 381                         if ( $job && $this->isRootJobOldDuplicate( $job ) ) {
 382                                 JobQueue::incrStats( 'dupe_pops', $this->type );
 383                                 $job = DuplicateJob::newFromJob( $job ); // convert to a no-op
 384                         }
 385                 } catch ( Exception $e ) {
 386                         // don't lose jobs over this
 387                 }
 388
 389                 return $job;
 390         }
 391
 392         /**
 393          * @see JobQueue::pop()
 394          * @return Job|bool
 395          */
 396         abstract protected function doPop();
 397
 398         /**
 399          * Acknowledge that a job was completed.
 400          *
 401          * This does nothing for certain queue classes or if "claimTTL" is not set.
 402          * Outside callers should use JobQueueGroup::ack() instead of this function.
 403          *
 404          * @param Job $job
 405          * @return void
 406          * @throws MWException
 407          */
 408         final public function ack( Job $job ) {
 409                 $this->assertNotReadOnly();
 410                 if ( $job->getType() !== $this->type ) {
 411                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 412                 }
 413
 414                 $this->doAck( $job );
 415         }
 416
 417         /**
 418          * @see JobQueue::ack()
 419          * @param Job $job
 420          */
 421         abstract protected function doAck( Job $job );
 422
 423         /**
 424          * Register the "root job" of a given job into the queue for de-duplication.
 425          * This should only be called right *after* all the new jobs have been inserted.
 426          * This is used to turn older, duplicate, job entries into no-ops. The root job
 427          * information will remain in the registry until it simply falls out of cache.
 428          *
 429          * This requires that $job has two special fields in the "params" array:
 430          *   - rootJobSignature : hash (e.g. SHA1) that identifies the task
 431          *   - rootJobTimestamp : TS_MW timestamp of this instance of the task
 432          *
 433          * A "root job" is a conceptual job that consist of potentially many smaller jobs
 434          * that are actually inserted into the queue. For example, "refreshLinks" jobs are
 435          * spawned when a template is edited. One can think of the task as "update links
 436          * of pages that use template X" and an instance of that task as a "root job".
 437          * However, what actually goes into the queue are range and leaf job subtypes.
 438          * Since these jobs include things like page ID ranges and DB master positions,
 439          * and can morph into smaller jobs recursively, simple duplicate detection
 440          * for individual jobs being identical (like that of job_sha1) is not useful.
 441          *
 442          * In the case of "refreshLinks", if these jobs are still in the queue when the template
 443          * is edited again, we want all of these old refreshLinks jobs for that template to become
 444          * no-ops. This can greatly reduce server load, since refreshLinks jobs involves parsing.
 445          * Essentially, the new batch of jobs belong to a new "root job" and the older ones to a
 446          * previous "root job" for the same task of "update links of pages that use template X".
 447          *
 448          * This does nothing for certain queue classes.
 449          *
 450          * @param IJobSpecification $job
 451          * @throws MWException
 452          * @return bool
 453          */
 454         final public function deduplicateRootJob( IJobSpecification $job ) {
 455                 $this->assertNotReadOnly();
 456                 if ( $job->getType() !== $this->type ) {
 457                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 458                 }
 459
 460                 return $this->doDeduplicateRootJob( $job );
 461         }
 462
 463         /**
 464          * @see JobQueue::deduplicateRootJob()
 465          * @param IJobSpecification $job
 466          * @throws MWException
 467          * @return bool
 468          */
 469         protected function doDeduplicateRootJob( IJobSpecification $job ) {
 470                 if ( !$job->hasRootJobParams() ) {
 471                         throw new MWException( "Cannot register root job; missing parameters." );
 472                 }
 473                 $params = $job->getRootJobParams();
 474
 475                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 476                 // Callers should call batchInsert() and then this function so that if the insert
 477                 // fails, the de-duplication registration will be aborted. Since the insert is
 478                 // deferred till "transaction idle", do the same here, so that the ordering is
 479                 // maintained. Having only the de-duplication registration succeed would cause
 480                 // jobs to become no-ops without any actual jobs that made them redundant.
 481                 $timestamp = $this->dupCache->get( $key ); // current last timestamp of this job
 482                 if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 483                         return true; // a newer version of this root job was enqueued
 484                 }
 485
 486                 // Update the timestamp of the last root job started at the location...
 487                 return $this->dupCache->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
 488         }
 489
 490         /**
 491          * Check if the "root" job of a given job has been superseded by a newer one
 492          *
 493          * @param Job $job
 494          * @throws MWException
 495          * @return bool
 496          */
 497         final protected function isRootJobOldDuplicate( Job $job ) {
 498                 if ( $job->getType() !== $this->type ) {
 499                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 500                 }
 501                 $isDuplicate = $this->doIsRootJobOldDuplicate( $job );
 502
 503                 return $isDuplicate;
 504         }
 505
 506         /**
 507          * @see JobQueue::isRootJobOldDuplicate()
 508          * @param Job $job
 509          * @return bool
 510          */
 511         protected function doIsRootJobOldDuplicate( Job $job ) {
 512                 if ( !$job->hasRootJobParams() ) {
 513                         return false; // job has no de-deplication info
 514                 }
 515                 $params = $job->getRootJobParams();
 516
 517                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 518                 // Get the last time this root job was enqueued
 519                 $timestamp = $this->dupCache->get( $key );
 520
 521                 // Check if a new root job was started at the location after this one's...
 522                 return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
 523         }
 524
 525         /**
 526          * @param string $signature Hash identifier of the root job
 527          * @return string
 528          */
 529         protected function getRootJobCacheKey( $signature ) {
 530                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 531
 532                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
 533         }
 534
 535         /**
 536          * Deleted all unclaimed and delayed jobs from the queue
 537          *
 538          * @throws JobQueueError
 539          * @since 1.22
 540          * @return void
 541          */
 542         final public function delete() {
 543                 $this->assertNotReadOnly();
 544
 545                 $this->doDelete();
 546         }
 547
 548         /**
 549          * @see JobQueue::delete()
 550          * @throws MWException
 551          */
 552         protected function doDelete() {
 553                 throw new MWException( "This method is not implemented." );
 554         }
 555
 556         /**
 557          * Wait for any replica DBs or backup servers to catch up.
 558          *
 559          * This does nothing for certain queue classes.
 560          *
 561          * @return void
 562          * @throws JobQueueError
 563          */
 564         final public function waitForBackups() {
 565                 $this->doWaitForBackups();
 566         }
 567
 568         /**
 569          * @see JobQueue::waitForBackups()
 570          * @return void
 571          */
 572         protected function doWaitForBackups() {
 573         }
 574
 575         /**
 576          * Clear any process and persistent caches
 577          *
 578          * @return void
 579          */
 580         final public function flushCaches() {
 581                 $this->doFlushCaches();
 582         }
 583
 584         /**
 585          * @see JobQueue::flushCaches()
 586          * @return void
 587          */
 588         protected function doFlushCaches() {
 589         }
 590
 591         /**
 592          * Get an iterator to traverse over all available jobs in this queue.
 593          * This does not include jobs that are currently acquired or delayed.
 594          * Note: results may be stale if the queue is concurrently modified.
 595          *
 596          * @return Iterator
 597          * @throws JobQueueError
 598          */
 599         abstract public function getAllQueuedJobs();
 600
 601         /**
 602          * Get an iterator to traverse over all delayed jobs in this queue.
 603          * Note: results may be stale if the queue is concurrently modified.
 604          *
 605          * @return Iterator
 606          * @throws JobQueueError
 607          * @since 1.22
 608          */
 609         public function getAllDelayedJobs() {
 610                 return new ArrayIterator( [] ); // not implemented
 611         }
 612
 613         /**
 614          * Get an iterator to traverse over all claimed jobs in this queue
 615          *
 616          * Callers should be quick to iterator over it or few results
 617          * will be returned due to jobs being acknowledged and deleted
 618          *
 619          * @return Iterator
 620          * @throws JobQueueError
 621          * @since 1.26
 622          */
 623         public function getAllAcquiredJobs() {
 624                 return new ArrayIterator( [] ); // not implemented
 625         }
 626
 627         /**
 628          * Get an iterator to traverse over all abandoned jobs in this queue
 629          *
 630          * @return Iterator
 631          * @throws JobQueueError
 632          * @since 1.25
 633          */
 634         public function getAllAbandonedJobs() {
 635                 return new ArrayIterator( [] ); // not implemented
 636         }
 637
 638         /**
 639          * Do not use this function outside of JobQueue/JobQueueGroup
 640          *
 641          * @return string
 642          * @since 1.22
 643          */
 644         public function getCoalesceLocationInternal() {
 645                 return null;
 646         }
 647
 648         /**
 649          * Check whether each of the given queues are empty.
 650          * This is used for batching checks for queues stored at the same place.
 651          *
 652          * @param array $types List of queues types
 653          * @return array|null (list of non-empty queue types) or null if unsupported
 654          * @throws MWException
 655          * @since 1.22
 656          */
 657         final public function getSiblingQueuesWithJobs( array $types ) {
 658                 return $this->doGetSiblingQueuesWithJobs( $types );
 659         }
 660
 661         /**
 662          * @see JobQueue::getSiblingQueuesWithJobs()
 663          * @param array $types List of queues types
 664          * @return array|null (list of queue types) or null if unsupported
 665          */
 666         protected function doGetSiblingQueuesWithJobs( array $types ) {
 667                 return null; // not supported
 668         }
 669
 670         /**
 671          * Check the size of each of the given queues.
 672          * For queues not served by the same store as this one, 0 is returned.
 673          * This is used for batching checks for queues stored at the same place.
 674          *
 675          * @param array $types List of queues types
 676          * @return array|null (job type => whether queue is empty) or null if unsupported
 677          * @throws MWException
 678          * @since 1.22
 679          */
 680         final public function getSiblingQueueSizes( array $types ) {
 681                 return $this->doGetSiblingQueueSizes( $types );
 682         }
 683
 684         /**
 685          * @see JobQueue::getSiblingQueuesSize()
 686          * @param array $types List of queues types
 687          * @return array|null (list of queue types) or null if unsupported
 688          */
 689         protected function doGetSiblingQueueSizes( array $types ) {
 690                 return null; // not supported
 691         }
 692
 693         /**
 694          * @throws JobQueueReadOnlyError
 695          */
 696         protected function assertNotReadOnly() {
 697                 if ( $this->readOnlyReason !== false ) {
 698                         throw new JobQueueReadOnlyError( "Job queue is read-only: {$this->readOnlyReason}" );
 699                 }
 700         }
 701
 702         /**
 703          * Call wfIncrStats() for the queue overall and for the queue type
 704          *
 705          * @param string $key Event type
 706          * @param string $type Job type
 707          * @param int $delta
 708          * @since 1.22
 709          */
 710         public static function incrStats( $key, $type, $delta = 1 ) {
 711                 static $stats;
 712                 if ( !$stats ) {
 713                         $stats = MediaWikiServices::getInstance()->getStatsdDataFactory();
 714                 }
 715                 $stats->updateCount( "jobqueue.{$key}.all", $delta );
 716                 $stats->updateCount( "jobqueue.{$key}.{$type}", $delta );
 717         }
 718 }
 719
 720 /**
 721  * @ingroup JobQueue
 722  * @since 1.22
 723  */
 724 class JobQueueError extends MWException {
 725 }
 726
 727 class JobQueueConnectionError extends JobQueueError {
 728 }
 729
 730 class JobQueueReadOnlyError extends JobQueueError {
 731
 732 }