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
  53         const QOS_ATOMIC = 1; // integer; "all-or-nothing" job insertions
  54
  55         const ROOTJOB_TTL = 2419200; // integer; seconds to remember root jobs (28 days)
  56
  57         /**
  58          * @param array $params
  59          * @throws MWException
  60          */
  61         protected function __construct( array $params ) {
  62                 $this->wiki = $params['wiki'];
  63                 $this->type = $params['type'];
  64                 $this->claimTTL = isset( $params['claimTTL'] ) ? $params['claimTTL'] : 0;
  65                 $this->maxTries = isset( $params['maxTries'] ) ? $params['maxTries'] : 3;
  66                 if ( isset( $params['order'] ) && $params['order'] !== 'any' ) {
  67                         $this->order = $params['order'];
  68                 } else {
  69                         $this->order = $this->optimalOrder();
  70                 }
  71                 if ( !in_array( $this->order, $this->supportedOrders() ) ) {
  72                         throw new MWException( __CLASS__ . " does not support '{$this->order}' order." );
  73                 }
  74                 $this->checkDelay = !empty( $params['checkDelay'] );
  75                 if ( $this->checkDelay && !$this->supportsDelayedJobs() ) {
  76                         throw new MWException( __CLASS__ . " does not support delayed jobs." );
  77                 }
  78                 $this->dupCache = wfGetCache( CACHE_ANYTHING );
  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 simple means re-inserting them into the queue. Jobs can be
 100          *                  attempted up to three times before being discarded.
 101          *   - checkDelay : If supported, respect Job::getReleaseTimestamp() in the push functions.
 102          *                  This lets delayed jobs wait in a staging area until a given timestamp is
 103          *                  reached, at which point they will enter the queue. If this is not enabled
 104          *                  or not supported, an exception will be thrown on delayed job insertion.
 105          *
 106          * Queue classes should throw an exception if they do not support the options given.
 107          *
 108          * @param array $params
 109          * @return JobQueue
 110          * @throws MWException
 111          */
 112         final public static function factory( array $params ) {
 113                 $class = $params['class'];
 114                 if ( !class_exists( $class ) ) {
 115                         throw new MWException( "Invalid job queue class '$class'." );
 116                 }
 117                 $obj = new $class( $params );
 118                 if ( !( $obj instanceof self ) ) {
 119                         throw new MWException( "Class '$class' is not a " . __CLASS__ . " class." );
 120                 }
 121
 122                 return $obj;
 123         }
 124
 125         /**
 126          * @return string Wiki ID
 127          */
 128         final public function getWiki() {
 129                 return $this->wiki;
 130         }
 131
 132         /**
 133          * @return string Job type that this queue handles
 134          */
 135         final public function getType() {
 136                 return $this->type;
 137         }
 138
 139         /**
 140          * @return string One of (random, timestamp, fifo, undefined)
 141          */
 142         final public function getOrder() {
 143                 return $this->order;
 144         }
 145
 146         /**
 147          * @return bool Whether delayed jobs are enabled
 148          * @since 1.22
 149          */
 150         final public function delayedJobsEnabled() {
 151                 return $this->checkDelay;
 152         }
 153
 154         /**
 155          * Get the allowed queue orders for configuration validation
 156          *
 157          * @return array Subset of (random, timestamp, fifo, undefined)
 158          */
 159         abstract protected function supportedOrders();
 160
 161         /**
 162          * Get the default queue order to use if configuration does not specify one
 163          *
 164          * @return string One of (random, timestamp, fifo, undefined)
 165          */
 166         abstract protected function optimalOrder();
 167
 168         /**
 169          * Find out if delayed jobs are supported for configuration validation
 170          *
 171          * @return bool Whether delayed jobs are supported
 172          */
 173         protected function supportsDelayedJobs() {
 174                 return false; // not implemented
 175         }
 176
 177         /**
 178          * Quickly check if the queue has no available (unacquired, non-delayed) jobs.
 179          * Queue classes should use caching if they are any slower without memcached.
 180          *
 181          * If caching is used, this might return false when there are actually no jobs.
 182          * If pop() is called and returns false then it should correct the cache. Also,
 183          * calling flushCaches() first prevents this. However, this affect is typically
 184          * not distinguishable from the race condition between isEmpty() and pop().
 185          *
 186          * @return bool
 187          * @throws JobQueueError
 188          */
 189         final public function isEmpty() {
 190                 wfProfileIn( __METHOD__ );
 191                 $res = $this->doIsEmpty();
 192                 wfProfileOut( __METHOD__ );
 193
 194                 return $res;
 195         }
 196
 197         /**
 198          * @see JobQueue::isEmpty()
 199          * @return bool
 200          */
 201         abstract protected function doIsEmpty();
 202
 203         /**
 204          * Get the number of available (unacquired, non-delayed) jobs in the queue.
 205          * Queue classes should use caching if they are any slower without memcached.
 206          *
 207          * If caching is used, this number might be out of date for a minute.
 208          *
 209          * @return int
 210          * @throws JobQueueError
 211          */
 212         final public function getSize() {
 213                 wfProfileIn( __METHOD__ );
 214                 $res = $this->doGetSize();
 215                 wfProfileOut( __METHOD__ );
 216
 217                 return $res;
 218         }
 219
 220         /**
 221          * @see JobQueue::getSize()
 222          * @return int
 223          */
 224         abstract protected function doGetSize();
 225
 226         /**
 227          * Get the number of acquired jobs (these are temporarily out of the queue).
 228          * Queue classes should use caching if they are any slower without memcached.
 229          *
 230          * If caching is used, this number might be out of date for a minute.
 231          *
 232          * @return int
 233          * @throws JobQueueError
 234          */
 235         final public function getAcquiredCount() {
 236                 wfProfileIn( __METHOD__ );
 237                 $res = $this->doGetAcquiredCount();
 238                 wfProfileOut( __METHOD__ );
 239
 240                 return $res;
 241         }
 242
 243         /**
 244          * @see JobQueue::getAcquiredCount()
 245          * @return int
 246          */
 247         abstract protected function doGetAcquiredCount();
 248
 249         /**
 250          * Get the number of delayed jobs (these are temporarily out of the queue).
 251          * Queue classes should use caching if they are any slower without memcached.
 252          *
 253          * If caching is used, this number might be out of date for a minute.
 254          *
 255          * @return int
 256          * @throws JobQueueError
 257          * @since 1.22
 258          */
 259         final public function getDelayedCount() {
 260                 wfProfileIn( __METHOD__ );
 261                 $res = $this->doGetDelayedCount();
 262                 wfProfileOut( __METHOD__ );
 263
 264                 return $res;
 265         }
 266
 267         /**
 268          * @see JobQueue::getDelayedCount()
 269          * @return int
 270          */
 271         protected function doGetDelayedCount() {
 272                 return 0; // not implemented
 273         }
 274
 275         /**
 276          * Get the number of acquired jobs that can no longer be attempted.
 277          * Queue classes should use caching if they are any slower without memcached.
 278          *
 279          * If caching is used, this number might be out of date for a minute.
 280          *
 281          * @return int
 282          * @throws JobQueueError
 283          */
 284         final public function getAbandonedCount() {
 285                 wfProfileIn( __METHOD__ );
 286                 $res = $this->doGetAbandonedCount();
 287                 wfProfileOut( __METHOD__ );
 288
 289                 return $res;
 290         }
 291
 292         /**
 293          * @see JobQueue::getAbandonedCount()
 294          * @return int
 295          */
 296         protected function doGetAbandonedCount() {
 297                 return 0; // not implemented
 298         }
 299
 300         /**
 301          * Push one or more jobs into the queue.
 302          * This does not require $wgJobClasses to be set for the given job type.
 303          * Outside callers should use JobQueueGroup::push() instead of this function.
 304          *
 305          * @param Job|array $jobs A single job or an array of Jobs
 306          * @param int $flags Bitfield (supports JobQueue::QOS_ATOMIC)
 307          * @return void
 308          * @throws JobQueueError
 309          */
 310         final public function push( $jobs, $flags = 0 ) {
 311                 $this->batchPush( is_array( $jobs ) ? $jobs : array( $jobs ), $flags );
 312         }
 313
 314         /**
 315          * Push a batch of jobs into the queue.
 316          * This does not require $wgJobClasses to be set for the given job type.
 317          * Outside callers should use JobQueueGroup::push() instead of this function.
 318          *
 319          * @param array $jobs List of Jobs
 320          * @param int $flags Bitfield (supports JobQueue::QOS_ATOMIC)
 321          * @return void
 322          * @throws MWException
 323          */
 324         final public function batchPush( array $jobs, $flags = 0 ) {
 325                 if ( !count( $jobs ) ) {
 326                         return; // nothing to do
 327                 }
 328
 329                 foreach ( $jobs as $job ) {
 330                         if ( $job->getType() !== $this->type ) {
 331                                 throw new MWException(
 332                                         "Got '{$job->getType()}' job; expected a '{$this->type}' job." );
 333                         } elseif ( $job->getReleaseTimestamp() && !$this->checkDelay ) {
 334                                 throw new MWException(
 335                                         "Got delayed '{$job->getType()}' job; delays are not supported." );
 336                         }
 337                 }
 338
 339                 wfProfileIn( __METHOD__ );
 340                 $this->doBatchPush( $jobs, $flags );
 341                 wfProfileOut( __METHOD__ );
 342         }
 343
 344         /**
 345          * @see JobQueue::batchPush()
 346          * @param array $jobs
 347          * @param int $flags
 348          */
 349         abstract protected function doBatchPush( array $jobs, $flags );
 350
 351         /**
 352          * Pop a job off of the queue.
 353          * This requires $wgJobClasses to be set for the given job type.
 354          * Outside callers should use JobQueueGroup::pop() instead of this function.
 355          *
 356          * @throws MWException
 357          * @return Job|bool Returns false if there are no jobs
 358          */
 359         final public function pop() {
 360                 global $wgJobClasses;
 361
 362                 if ( $this->wiki !== wfWikiID() ) {
 363                         throw new MWException( "Cannot pop '{$this->type}' job off foreign wiki queue." );
 364                 } elseif ( !isset( $wgJobClasses[$this->type] ) ) {
 365                         // Do not pop jobs if there is no class for the queue type
 366                         throw new MWException( "Unrecognized job type '{$this->type}'." );
 367                 }
 368
 369                 wfProfileIn( __METHOD__ );
 370                 $job = $this->doPop();
 371                 wfProfileOut( __METHOD__ );
 372
 373                 // Flag this job as an old duplicate based on its "root" job...
 374                 try {
 375                         if ( $job && $this->isRootJobOldDuplicate( $job ) ) {
 376                                 JobQueue::incrStats( 'job-pop-duplicate', $this->type, 1, $this->wiki );
 377                                 $job = DuplicateJob::newFromJob( $job ); // convert to a no-op
 378                         }
 379                 } catch ( MWException $e ) {
 380                         // don't lose jobs over this
 381                 }
 382
 383                 return $job;
 384         }
 385
 386         /**
 387          * @see JobQueue::pop()
 388          * @return Job
 389          */
 390         abstract protected function doPop();
 391
 392         /**
 393          * Acknowledge that a job was completed.
 394          *
 395          * This does nothing for certain queue classes or if "claimTTL" is not set.
 396          * Outside callers should use JobQueueGroup::ack() instead of this function.
 397          *
 398          * @param Job $job
 399          * @return void
 400          * @throws MWException
 401          */
 402         final public function ack( Job $job ) {
 403                 if ( $job->getType() !== $this->type ) {
 404                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 405                 }
 406                 wfProfileIn( __METHOD__ );
 407                 $this->doAck( $job );
 408                 wfProfileOut( __METHOD__ );
 409         }
 410
 411         /**
 412          * @see JobQueue::ack()
 413          * @param Job $job
 414          */
 415         abstract protected function doAck( Job $job );
 416
 417         /**
 418          * Register the "root job" of a given job into the queue for de-duplication.
 419          * This should only be called right *after* all the new jobs have been inserted.
 420          * This is used to turn older, duplicate, job entries into no-ops. The root job
 421          * information will remain in the registry until it simply falls out of cache.
 422          *
 423          * This requires that $job has two special fields in the "params" array:
 424          *   - rootJobSignature : hash (e.g. SHA1) that identifies the task
 425          *   - rootJobTimestamp : TS_MW timestamp of this instance of the task
 426          *
 427          * A "root job" is a conceptual job that consist of potentially many smaller jobs
 428          * that are actually inserted into the queue. For example, "refreshLinks" jobs are
 429          * spawned when a template is edited. One can think of the task as "update links
 430          * of pages that use template X" and an instance of that task as a "root job".
 431          * However, what actually goes into the queue are range and leaf job subtypes.
 432          * Since these jobs include things like page ID ranges and DB master positions,
 433          * and can morph into smaller jobs recursively, simple duplicate detection
 434          * for individual jobs being identical (like that of job_sha1) is not useful.
 435          *
 436          * In the case of "refreshLinks", if these jobs are still in the queue when the template
 437          * is edited again, we want all of these old refreshLinks jobs for that template to become
 438          * no-ops. This can greatly reduce server load, since refreshLinks jobs involves parsing.
 439          * Essentially, the new batch of jobs belong to a new "root job" and the older ones to a
 440          * previous "root job" for the same task of "update links of pages that use template X".
 441          *
 442          * This does nothing for certain queue classes.
 443          *
 444          * @param Job $job
 445          * @throws MWException
 446          * @return bool
 447          */
 448         final public function deduplicateRootJob( Job $job ) {
 449                 if ( $job->getType() !== $this->type ) {
 450                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 451                 }
 452                 wfProfileIn( __METHOD__ );
 453                 $ok = $this->doDeduplicateRootJob( $job );
 454                 wfProfileOut( __METHOD__ );
 455
 456                 return $ok;
 457         }
 458
 459         /**
 460          * @see JobQueue::deduplicateRootJob()
 461          * @param Job $job
 462          * @throws MWException
 463          * @return bool
 464          */
 465         protected function doDeduplicateRootJob( Job $job ) {
 466                 if ( !$job->hasRootJobParams() ) {
 467                         throw new MWException( "Cannot register root job; missing parameters." );
 468                 }
 469                 $params = $job->getRootJobParams();
 470
 471                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 472                 // Callers should call batchInsert() and then this function so that if the insert
 473                 // fails, the de-duplication registration will be aborted. Since the insert is
 474                 // deferred till "transaction idle", do the same here, so that the ordering is
 475                 // maintained. Having only the de-duplication registration succeed would cause
 476                 // jobs to become no-ops without any actual jobs that made them redundant.
 477                 $timestamp = $this->dupCache->get( $key ); // current last timestamp of this job
 478                 if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 479                         return true; // a newer version of this root job was enqueued
 480                 }
 481
 482                 // Update the timestamp of the last root job started at the location...
 483                 return $this->dupCache->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
 484         }
 485
 486         /**
 487          * Check if the "root" job of a given job has been superseded by a newer one
 488          *
 489          * @param Job $job
 490          * @throws MWException
 491          * @return bool
 492          */
 493         final protected function isRootJobOldDuplicate( Job $job ) {
 494                 if ( $job->getType() !== $this->type ) {
 495                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 496                 }
 497                 wfProfileIn( __METHOD__ );
 498                 $isDuplicate = $this->doIsRootJobOldDuplicate( $job );
 499                 wfProfileOut( __METHOD__ );
 500
 501                 return $isDuplicate;
 502         }
 503
 504         /**
 505          * @see JobQueue::isRootJobOldDuplicate()
 506          * @param Job $job
 507          * @return bool
 508          */
 509         protected function doIsRootJobOldDuplicate( Job $job ) {
 510                 if ( !$job->hasRootJobParams() ) {
 511                         return false; // job has no de-deplication info
 512                 }
 513                 $params = $job->getRootJobParams();
 514
 515                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 516                 // Get the last time this root job was enqueued
 517                 $timestamp = $this->dupCache->get( $key );
 518
 519                 // Check if a new root job was started at the location after this one's...
 520                 return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
 521         }
 522
 523         /**
 524          * @param string $signature Hash identifier of the root job
 525          * @return string
 526          */
 527         protected function getRootJobCacheKey( $signature ) {
 528                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 529
 530                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
 531         }
 532
 533         /**
 534          * Deleted all unclaimed and delayed jobs from the queue
 535          *
 536          * @throws JobQueueError
 537          * @since 1.22
 538          * @return void
 539          */
 540         final public function delete() {
 541                 wfProfileIn( __METHOD__ );
 542                 $this->doDelete();
 543                 wfProfileOut( __METHOD__ );
 544         }
 545
 546         /**
 547          * @see JobQueue::delete()
 548          * @throws MWException
 549          */
 550         protected function doDelete() {
 551                 throw new MWException( "This method is not implemented." );
 552         }
 553
 554         /**
 555          * Wait for any slaves or backup servers to catch up.
 556          *
 557          * This does nothing for certain queue classes.
 558          *
 559          * @return void
 560          * @throws JobQueueError
 561          */
 562         final public function waitForBackups() {
 563                 wfProfileIn( __METHOD__ );
 564                 $this->doWaitForBackups();
 565                 wfProfileOut( __METHOD__ );
 566         }
 567
 568         /**
 569          * @see JobQueue::waitForBackups()
 570          * @return void
 571          */
 572         protected function doWaitForBackups() {
 573         }
 574
 575         /**
 576          * Return a map of task names to task definition maps.
 577          * A "task" is a fast periodic queue maintenance action.
 578          * Mutually exclusive tasks must implement their own locking in the callback.
 579          *
 580          * Each task value is an associative array with:
 581          *   - name     : the name of the task
 582          *   - callback : a PHP callable that performs the task
 583          *   - period   : the period in seconds corresponding to the task frequency
 584          *
 585          * @return array
 586          */
 587         final public function getPeriodicTasks() {
 588                 $tasks = $this->doGetPeriodicTasks();
 589                 foreach ( $tasks as $name => &$def ) {
 590                         $def['name'] = $name;
 591                 }
 592
 593                 return $tasks;
 594         }
 595
 596         /**
 597          * @see JobQueue::getPeriodicTasks()
 598          * @return array
 599          */
 600         protected function doGetPeriodicTasks() {
 601                 return array();
 602         }
 603
 604         /**
 605          * Clear any process and persistent caches
 606          *
 607          * @return void
 608          */
 609         final public function flushCaches() {
 610                 wfProfileIn( __METHOD__ );
 611                 $this->doFlushCaches();
 612                 wfProfileOut( __METHOD__ );
 613         }
 614
 615         /**
 616          * @see JobQueue::flushCaches()
 617          * @return void
 618          */
 619         protected function doFlushCaches() {
 620         }
 621
 622         /**
 623          * Get an iterator to traverse over all available jobs in this queue.
 624          * This does not include jobs that are currently acquired or delayed.
 625          * Note: results may be stale if the queue is concurrently modified.
 626          *
 627          * @return Iterator
 628          * @throws JobQueueError
 629          */
 630         abstract public function getAllQueuedJobs();
 631
 632         /**
 633          * Get an iterator to traverse over all delayed jobs in this queue.
 634          * Note: results may be stale if the queue is concurrently modified.
 635          *
 636          * @return Iterator
 637          * @throws JobQueueError
 638          * @since 1.22
 639          */
 640         public function getAllDelayedJobs() {
 641                 return new ArrayIterator( array() ); // not implemented
 642         }
 643
 644         /**
 645          * Do not use this function outside of JobQueue/JobQueueGroup
 646          *
 647          * @return string
 648          * @since 1.22
 649          */
 650         public function getCoalesceLocationInternal() {
 651                 return null;
 652         }
 653
 654         /**
 655          * Check whether each of the given queues are empty.
 656          * This is used for batching checks for queues stored at the same place.
 657          *
 658          * @param array $types List of queues types
 659          * @return array|null (list of non-empty queue types) or null if unsupported
 660          * @throws MWException
 661          * @since 1.22
 662          */
 663         final public function getSiblingQueuesWithJobs( array $types ) {
 664                 $section = new ProfileSection( __METHOD__ );
 665
 666                 return $this->doGetSiblingQueuesWithJobs( $types );
 667         }
 668
 669         /**
 670          * @see JobQueue::getSiblingQueuesWithJobs()
 671          * @param array $types List of queues types
 672          * @return array|null (list of queue types) or null if unsupported
 673          */
 674         protected function doGetSiblingQueuesWithJobs( array $types ) {
 675                 return null; // not supported
 676         }
 677
 678         /**
 679          * Check the size of each of the given queues.
 680          * For queues not served by the same store as this one, 0 is returned.
 681          * This is used for batching checks for queues stored at the same place.
 682          *
 683          * @param array $types List of queues types
 684          * @return array|null (job type => whether queue is empty) or null if unsupported
 685          * @throws MWException
 686          * @since 1.22
 687          */
 688         final public function getSiblingQueueSizes( array $types ) {
 689                 $section = new ProfileSection( __METHOD__ );
 690
 691                 return $this->doGetSiblingQueueSizes( $types );
 692         }
 693
 694         /**
 695          * @see JobQueue::getSiblingQueuesSize()
 696          * @param array $types List of queues types
 697          * @return array|null (list of queue types) or null if unsupported
 698          */
 699         protected function doGetSiblingQueueSizes( array $types ) {
 700                 return null; // not supported
 701         }
 702
 703         /**
 704          * Call wfIncrStats() for the queue overall and for the queue type
 705          *
 706          * @param string $key Event type
 707          * @param string $type Job type
 708          * @param int $delta
 709          * @param string $wiki Wiki ID (added in 1.23)
 710          * @since 1.22
 711          */
 712         public static function incrStats( $key, $type, $delta = 1, $wiki = null ) {
 713                 wfIncrStats( $key, $delta );
 714                 wfIncrStats( "{$key}-{$type}", $delta );
 715                 if ( $wiki !== null ) {
 716                         wfIncrStats( "{$key}-{$type}-{$wiki}", $delta );
 717                 }
 718         }
 719
 720         /**
 721          * Namespace the queue with a key to isolate it for testing
 722          *
 723          * @param string $key
 724          * @return void
 725          * @throws MWException
 726          */
 727         public function setTestingPrefix( $key ) {
 728                 throw new MWException( "Queue namespacing not supported for this queue type." );
 729         }
 730 }
 731
 732 /**
 733  * @ingroup JobQueue
 734  * @since 1.22
 735  */
 736 class JobQueueError extends MWException {
 737 }
 738
 739 class JobQueueConnectionError extends JobQueueError {
 740 }