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
  25 /**
  26  * Class to handle enqueueing and running of background jobs
  27  *
  28  * @ingroup JobQueue
  29  * @since 1.21
  30  */
  31 abstract class JobQueue {
  32         /** @var string Wiki ID */
  33         protected $wiki;
  34
  35         /** @var string Job type */
  36         protected $type;
  37
  38         /** @var string Job priority for pop() */
  39         protected $order;
  40
  41         /** @var int Time to live in seconds */
  42         protected $claimTTL;
  43
  44         /** @var int Maximum number of times to try a job */
  45         protected $maxTries;
  46
  47         /** @var bool Allow delayed jobs */
  48         protected $checkDelay;
  49
  50         /** @var BagOStuff */
  51         protected $dupCache;
  52         /** @var JobQueueAggregator */
  53         protected $aggr;
  54
  55         const QOS_ATOMIC = 1; // integer; "all-or-nothing" job insertions
  56
  57         const ROOTJOB_TTL = 2419200; // integer; seconds to remember root jobs (28 days)
  58
  59         /**
  60          * @param array $params
  61          * @throws MWException
  62          */
  63         protected function __construct( array $params ) {
  64                 $this->wiki = $params['wiki'];
  65                 $this->type = $params['type'];
  66                 $this->claimTTL = isset( $params['claimTTL'] ) ? $params['claimTTL'] : 0;
  67                 $this->maxTries = isset( $params['maxTries'] ) ? $params['maxTries'] : 3;
  68                 if ( isset( $params['order'] ) && $params['order'] !== 'any' ) {
  69                         $this->order = $params['order'];
  70                 } else {
  71                         $this->order = $this->optimalOrder();
  72                 }
  73                 if ( !in_array( $this->order, $this->supportedOrders() ) ) {
  74                         throw new MWException( __CLASS__ . " does not support '{$this->order}' order." );
  75                 }
  76                 $this->checkDelay = !empty( $params['checkDelay'] );
  77                 if ( $this->checkDelay && !$this->supportsDelayedJobs() ) {
  78                         throw new MWException( __CLASS__ . " does not support delayed jobs." );
  79                 }
  80                 $this->dupCache = wfGetCache( CACHE_ANYTHING );
  81                 $this->aggr = isset( $params['aggregator'] )
  82                         ? $params['aggregator']
  83                         : new JobQueueAggregatorNull( array() );
  84         }
  85
  86         /**
  87          * Get a job queue object of the specified type.
  88          * $params includes:
  89          *   - class      : What job class to use (determines job type)
  90          *   - wiki       : wiki ID of the wiki the jobs are for (defaults to current wiki)
  91          *   - type       : The name of the job types this queue handles
  92          *   - order      : Order that pop() selects jobs, one of "fifo", "timestamp" or "random".
  93          *                  If "fifo" is used, the queue will effectively be FIFO. Note that job
  94          *                  completion will not appear to be exactly FIFO if there are multiple
  95          *                  job runners since jobs can take different times to finish once popped.
  96          *                  If "timestamp" is used, the queue will at least be loosely ordered
  97          *                  by timestamp, allowing for some jobs to be popped off out of order.
  98          *                  If "random" is used, pop() will pick jobs in random order.
  99          *                  Note that it may only be weakly random (e.g. a lottery of the oldest X).
 100          *                  If "any" is choosen, the queue will use whatever order is the fastest.
 101          *                  This might be useful for improving concurrency for job acquisition.
 102          *   - claimTTL   : If supported, the queue will recycle jobs that have been popped
 103          *                  but not acknowledged as completed after this many seconds. Recycling
 104          *                  of jobs simple means re-inserting them into the queue. Jobs can be
 105          *                  attempted up to three times before being discarded.
 106          *   - checkDelay : If supported, respect Job::getReleaseTimestamp() in the push functions.
 107          *                  This lets delayed jobs wait in a staging area until a given timestamp is
 108          *                  reached, at which point they will enter the queue. If this is not enabled
 109          *                  or not supported, an exception will be thrown on delayed job insertion.
 110          *
 111          * Queue classes should throw an exception if they do not support the options given.
 112          *
 113          * @param array $params
 114          * @return JobQueue
 115          * @throws MWException
 116          */
 117         final public static function factory( array $params ) {
 118                 $class = $params['class'];
 119                 if ( !class_exists( $class ) ) {
 120                         throw new MWException( "Invalid job queue class '$class'." );
 121                 }
 122                 $obj = new $class( $params );
 123                 if ( !( $obj instanceof self ) ) {
 124                         throw new MWException( "Class '$class' is not a " . __CLASS__ . " class." );
 125                 }
 126
 127                 return $obj;
 128         }
 129
 130         /**
 131          * @return string Wiki ID
 132          */
 133         final public function getWiki() {
 134                 return $this->wiki;
 135         }
 136
 137         /**
 138          * @return string Job type that this queue handles
 139          */
 140         final public function getType() {
 141                 return $this->type;
 142         }
 143
 144         /**
 145          * @return string One of (random, timestamp, fifo, undefined)
 146          */
 147         final public function getOrder() {
 148                 return $this->order;
 149         }
 150
 151         /**
 152          * @return bool Whether delayed jobs are enabled
 153          * @since 1.22
 154          */
 155         final public function delayedJobsEnabled() {
 156                 return $this->checkDelay;
 157         }
 158
 159         /**
 160          * Get the allowed queue orders for configuration validation
 161          *
 162          * @return array Subset of (random, timestamp, fifo, undefined)
 163          */
 164         abstract protected function supportedOrders();
 165
 166         /**
 167          * Get the default queue order to use if configuration does not specify one
 168          *
 169          * @return string One of (random, timestamp, fifo, undefined)
 170          */
 171         abstract protected function optimalOrder();
 172
 173         /**
 174          * Find out if delayed jobs are supported for configuration validation
 175          *
 176          * @return bool Whether delayed jobs are supported
 177          */
 178         protected function supportsDelayedJobs() {
 179                 return false; // not implemented
 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 Job|array $jobs A single job or an array of 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 : array( $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 array $jobs List of 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                 if ( !count( $jobs ) ) {
 322                         return; // nothing to do
 323                 }
 324
 325                 foreach ( $jobs as $job ) {
 326                         if ( $job->getType() !== $this->type ) {
 327                                 throw new MWException(
 328                                         "Got '{$job->getType()}' job; expected a '{$this->type}' job." );
 329                         } elseif ( $job->getReleaseTimestamp() && !$this->checkDelay ) {
 330                                 throw new MWException(
 331                                         "Got delayed '{$job->getType()}' job; delays are not supported." );
 332                         }
 333                 }
 334
 335                 $this->doBatchPush( $jobs, $flags );
 336                 $this->aggr->notifyQueueNonEmpty( $this->wiki, $this->type );
 337         }
 338
 339         /**
 340          * @see JobQueue::batchPush()
 341          * @param array $jobs
 342          * @param int $flags
 343          */
 344         abstract protected function doBatchPush( array $jobs, $flags );
 345
 346         /**
 347          * Pop a job off of the queue.
 348          * This requires $wgJobClasses to be set for the given job type.
 349          * Outside callers should use JobQueueGroup::pop() instead of this function.
 350          *
 351          * @throws MWException
 352          * @return Job|bool Returns false if there are no jobs
 353          */
 354         final public function pop() {
 355                 global $wgJobClasses;
 356
 357                 if ( $this->wiki !== wfWikiID() ) {
 358                         throw new MWException( "Cannot pop '{$this->type}' job off foreign wiki queue." );
 359                 } elseif ( !isset( $wgJobClasses[$this->type] ) ) {
 360                         // Do not pop jobs if there is no class for the queue type
 361                         throw new MWException( "Unrecognized job type '{$this->type}'." );
 362                 }
 363
 364                 $job = $this->doPop();
 365
 366                 if ( !$job ) {
 367                         $this->aggr->notifyQueueEmpty( $this->wiki, $this->type );
 368                 }
 369
 370                 // Flag this job as an old duplicate based on its "root" job...
 371                 try {
 372                         if ( $job && $this->isRootJobOldDuplicate( $job ) ) {
 373                                 JobQueue::incrStats( 'job-pop-duplicate', $this->type, 1, $this->wiki );
 374                                 $job = DuplicateJob::newFromJob( $job ); // convert to a no-op
 375                         }
 376                 } catch ( Exception $e ) {
 377                         // don't lose jobs over this
 378                 }
 379
 380                 return $job;
 381         }
 382
 383         /**
 384          * @see JobQueue::pop()
 385          * @return Job
 386          */
 387         abstract protected function doPop();
 388
 389         /**
 390          * Acknowledge that a job was completed.
 391          *
 392          * This does nothing for certain queue classes or if "claimTTL" is not set.
 393          * Outside callers should use JobQueueGroup::ack() instead of this function.
 394          *
 395          * @param Job $job
 396          * @return void
 397          * @throws MWException
 398          */
 399         final public function ack( Job $job ) {
 400                 if ( $job->getType() !== $this->type ) {
 401                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 402                 }
 403                 $this->doAck( $job );
 404         }
 405
 406         /**
 407          * @see JobQueue::ack()
 408          * @param Job $job
 409          */
 410         abstract protected function doAck( Job $job );
 411
 412         /**
 413          * Register the "root job" of a given job into the queue for de-duplication.
 414          * This should only be called right *after* all the new jobs have been inserted.
 415          * This is used to turn older, duplicate, job entries into no-ops. The root job
 416          * information will remain in the registry until it simply falls out of cache.
 417          *
 418          * This requires that $job has two special fields in the "params" array:
 419          *   - rootJobSignature : hash (e.g. SHA1) that identifies the task
 420          *   - rootJobTimestamp : TS_MW timestamp of this instance of the task
 421          *
 422          * A "root job" is a conceptual job that consist of potentially many smaller jobs
 423          * that are actually inserted into the queue. For example, "refreshLinks" jobs are
 424          * spawned when a template is edited. One can think of the task as "update links
 425          * of pages that use template X" and an instance of that task as a "root job".
 426          * However, what actually goes into the queue are range and leaf job subtypes.
 427          * Since these jobs include things like page ID ranges and DB master positions,
 428          * and can morph into smaller jobs recursively, simple duplicate detection
 429          * for individual jobs being identical (like that of job_sha1) is not useful.
 430          *
 431          * In the case of "refreshLinks", if these jobs are still in the queue when the template
 432          * is edited again, we want all of these old refreshLinks jobs for that template to become
 433          * no-ops. This can greatly reduce server load, since refreshLinks jobs involves parsing.
 434          * Essentially, the new batch of jobs belong to a new "root job" and the older ones to a
 435          * previous "root job" for the same task of "update links of pages that use template X".
 436          *
 437          * This does nothing for certain queue classes.
 438          *
 439          * @param Job $job
 440          * @throws MWException
 441          * @return bool
 442          */
 443         final public function deduplicateRootJob( Job $job ) {
 444                 if ( $job->getType() !== $this->type ) {
 445                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 446                 }
 447                 $ok = $this->doDeduplicateRootJob( $job );
 448
 449                 return $ok;
 450         }
 451
 452         /**
 453          * @see JobQueue::deduplicateRootJob()
 454          * @param Job $job
 455          * @throws MWException
 456          * @return bool
 457          */
 458         protected function doDeduplicateRootJob( Job $job ) {
 459                 if ( !$job->hasRootJobParams() ) {
 460                         throw new MWException( "Cannot register root job; missing parameters." );
 461                 }
 462                 $params = $job->getRootJobParams();
 463
 464                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 465                 // Callers should call batchInsert() and then this function so that if the insert
 466                 // fails, the de-duplication registration will be aborted. Since the insert is
 467                 // deferred till "transaction idle", do the same here, so that the ordering is
 468                 // maintained. Having only the de-duplication registration succeed would cause
 469                 // jobs to become no-ops without any actual jobs that made them redundant.
 470                 $timestamp = $this->dupCache->get( $key ); // current last timestamp of this job
 471                 if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 472                         return true; // a newer version of this root job was enqueued
 473                 }
 474
 475                 // Update the timestamp of the last root job started at the location...
 476                 return $this->dupCache->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
 477         }
 478
 479         /**
 480          * Check if the "root" job of a given job has been superseded by a newer one
 481          *
 482          * @param Job $job
 483          * @throws MWException
 484          * @return bool
 485          */
 486         final protected function isRootJobOldDuplicate( Job $job ) {
 487                 if ( $job->getType() !== $this->type ) {
 488                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 489                 }
 490                 $isDuplicate = $this->doIsRootJobOldDuplicate( $job );
 491
 492                 return $isDuplicate;
 493         }
 494
 495         /**
 496          * @see JobQueue::isRootJobOldDuplicate()
 497          * @param Job $job
 498          * @return bool
 499          */
 500         protected function doIsRootJobOldDuplicate( Job $job ) {
 501                 if ( !$job->hasRootJobParams() ) {
 502                         return false; // job has no de-deplication info
 503                 }
 504                 $params = $job->getRootJobParams();
 505
 506                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 507                 // Get the last time this root job was enqueued
 508                 $timestamp = $this->dupCache->get( $key );
 509
 510                 // Check if a new root job was started at the location after this one's...
 511                 return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
 512         }
 513
 514         /**
 515          * @param string $signature Hash identifier of the root job
 516          * @return string
 517          */
 518         protected function getRootJobCacheKey( $signature ) {
 519                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 520
 521                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
 522         }
 523
 524         /**
 525          * Deleted all unclaimed and delayed jobs from the queue
 526          *
 527          * @throws JobQueueError
 528          * @since 1.22
 529          * @return void
 530          */
 531         final public function delete() {
 532                 $this->doDelete();
 533         }
 534
 535         /**
 536          * @see JobQueue::delete()
 537          * @throws MWException
 538          */
 539         protected function doDelete() {
 540                 throw new MWException( "This method is not implemented." );
 541         }
 542
 543         /**
 544          * Wait for any slaves or backup servers to catch up.
 545          *
 546          * This does nothing for certain queue classes.
 547          *
 548          * @return void
 549          * @throws JobQueueError
 550          */
 551         final public function waitForBackups() {
 552                 $this->doWaitForBackups();
 553         }
 554
 555         /**
 556          * @see JobQueue::waitForBackups()
 557          * @return void
 558          */
 559         protected function doWaitForBackups() {
 560         }
 561
 562         /**
 563          * Return a map of task names to task definition maps.
 564          * A "task" is a fast periodic queue maintenance action.
 565          * Mutually exclusive tasks must implement their own locking in the callback.
 566          *
 567          * Each task value is an associative array with:
 568          *   - name     : the name of the task
 569          *   - callback : a PHP callable that performs the task
 570          *   - period   : the period in seconds corresponding to the task frequency
 571          *
 572          * @return array
 573          */
 574         final public function getPeriodicTasks() {
 575                 $tasks = $this->doGetPeriodicTasks();
 576                 foreach ( $tasks as $name => &$def ) {
 577                         $def['name'] = $name;
 578                 }
 579
 580                 return $tasks;
 581         }
 582
 583         /**
 584          * @see JobQueue::getPeriodicTasks()
 585          * @return array
 586          */
 587         protected function doGetPeriodicTasks() {
 588                 return array();
 589         }
 590
 591         /**
 592          * Clear any process and persistent caches
 593          *
 594          * @return void
 595          */
 596         final public function flushCaches() {
 597                 $this->doFlushCaches();
 598         }
 599
 600         /**
 601          * @see JobQueue::flushCaches()
 602          * @return void
 603          */
 604         protected function doFlushCaches() {
 605         }
 606
 607         /**
 608          * Get an iterator to traverse over all available jobs in this queue.
 609          * This does not include jobs that are currently acquired or delayed.
 610          * Note: results may be stale if the queue is concurrently modified.
 611          *
 612          * @return Iterator
 613          * @throws JobQueueError
 614          */
 615         abstract public function getAllQueuedJobs();
 616
 617         /**
 618          * Get an iterator to traverse over all delayed jobs in this queue.
 619          * Note: results may be stale if the queue is concurrently modified.
 620          *
 621          * @return Iterator
 622          * @throws JobQueueError
 623          * @since 1.22
 624          */
 625         public function getAllDelayedJobs() {
 626                 return new ArrayIterator( array() ); // not implemented
 627         }
 628
 629         /**
 630          * Do not use this function outside of JobQueue/JobQueueGroup
 631          *
 632          * @return string
 633          * @since 1.22
 634          */
 635         public function getCoalesceLocationInternal() {
 636                 return null;
 637         }
 638
 639         /**
 640          * Check whether each of the given queues are empty.
 641          * This is used for batching checks for queues stored at the same place.
 642          *
 643          * @param array $types List of queues types
 644          * @return array|null (list of non-empty queue types) or null if unsupported
 645          * @throws MWException
 646          * @since 1.22
 647          */
 648         final public function getSiblingQueuesWithJobs( array $types ) {
 649
 650                 return $this->doGetSiblingQueuesWithJobs( $types );
 651         }
 652
 653         /**
 654          * @see JobQueue::getSiblingQueuesWithJobs()
 655          * @param array $types List of queues types
 656          * @return array|null (list of queue types) or null if unsupported
 657          */
 658         protected function doGetSiblingQueuesWithJobs( array $types ) {
 659                 return null; // not supported
 660         }
 661
 662         /**
 663          * Check the size of each of the given queues.
 664          * For queues not served by the same store as this one, 0 is returned.
 665          * This is used for batching checks for queues stored at the same place.
 666          *
 667          * @param array $types List of queues types
 668          * @return array|null (job type => whether queue is empty) or null if unsupported
 669          * @throws MWException
 670          * @since 1.22
 671          */
 672         final public function getSiblingQueueSizes( array $types ) {
 673
 674                 return $this->doGetSiblingQueueSizes( $types );
 675         }
 676
 677         /**
 678          * @see JobQueue::getSiblingQueuesSize()
 679          * @param array $types List of queues types
 680          * @return array|null (list of queue types) or null if unsupported
 681          */
 682         protected function doGetSiblingQueueSizes( array $types ) {
 683                 return null; // not supported
 684         }
 685
 686         /**
 687          * Call wfIncrStats() for the queue overall and for the queue type
 688          *
 689          * @param string $key Event type
 690          * @param string $type Job type
 691          * @param int $delta
 692          * @param string $wiki Wiki ID (added in 1.23)
 693          * @since 1.22
 694          */
 695         public static function incrStats( $key, $type, $delta = 1, $wiki = null ) {
 696                 wfIncrStats( $key, $delta );
 697                 wfIncrStats( "{$key}-{$type}", $delta );
 698                 if ( $wiki !== null ) {
 699                         wfIncrStats( "{$key}-{$type}-{$wiki}", $delta );
 700                 }
 701         }
 702
 703         /**
 704          * Namespace the queue with a key to isolate it for testing
 705          *
 706          * @param string $key
 707          * @return void
 708          * @throws MWException
 709          */
 710         public function setTestingPrefix( $key ) {
 711                 throw new MWException( "Queue namespacing not supported for this queue type." );
 712         }
 713 }
 714
 715 /**
 716  * @ingroup JobQueue
 717  * @since 1.22
 718  */
 719 class JobQueueError extends MWException {
 720 }
 721
 722 class JobQueueConnectionError extends JobQueueError {
 723 }