includes/job/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         protected $wiki; // string; wiki ID
  33         protected $type; // string; job type
  34         protected $order; // string; job priority for pop()
  35         protected $claimTTL; // integer; seconds
  36         protected $maxTries; // integer; maximum number of times to try a job
  37         protected $checkDelay; // boolean; allow delayed jobs
  38
  39         /** @var BagOStuff */
  40         protected $dupCache;
  41
  42         const QOS_ATOMIC = 1; // integer; "all-or-nothing" job insertions
  43
  44         const ROOTJOB_TTL = 2419200; // integer; seconds to remember root jobs (28 days)
  45
  46         /**
  47          * @param $params array
  48          */
  49         protected function __construct( array $params ) {
  50                 $this->wiki = $params['wiki'];
  51                 $this->type = $params['type'];
  52                 $this->claimTTL = isset( $params['claimTTL'] ) ? $params['claimTTL'] : 0;
  53                 $this->maxTries = isset( $params['maxTries'] ) ? $params['maxTries'] : 3;
  54                 if ( isset( $params['order'] ) && $params['order'] !== 'any' ) {
  55                         $this->order = $params['order'];
  56                 } else {
  57                         $this->order = $this->optimalOrder();
  58                 }
  59                 if ( !in_array( $this->order, $this->supportedOrders() ) ) {
  60                         throw new MWException( __CLASS__ . " does not support '{$this->order}' order." );
  61                 }
  62                 $this->checkDelay = !empty( $params['checkDelay'] );
  63                 if ( $this->checkDelay && !$this->supportsDelayedJobs() ) {
  64                         throw new MWException( __CLASS__ . " does not support delayed jobs." );
  65                 }
  66                 $this->dupCache = wfGetCache( CACHE_ANYTHING );
  67         }
  68
  69         /**
  70          * Get a job queue object of the specified type.
  71          * $params includes:
  72          *   - class      : What job class to use (determines job type)
  73          *   - wiki       : wiki ID of the wiki the jobs are for (defaults to current wiki)
  74          *   - type       : The name of the job types this queue handles
  75          *   - order      : Order that pop() selects jobs, one of "fifo", "timestamp" or "random".
  76          *                  If "fifo" is used, the queue will effectively be FIFO. Note that job
  77          *                  completion will not appear to be exactly FIFO if there are multiple
  78          *                  job runners since jobs can take different times to finish once popped.
  79          *                  If "timestamp" is used, the queue will at least be loosely ordered
  80          *                  by timestamp, allowing for some jobs to be popped off out of order.
  81          *                  If "random" is used, pop() will pick jobs in random order.
  82          *                  Note that it may only be weakly random (e.g. a lottery of the oldest X).
  83          *                  If "any" is choosen, the queue will use whatever order is the fastest.
  84          *                  This might be useful for improving concurrency for job acquisition.
  85          *   - claimTTL   : If supported, the queue will recycle jobs that have been popped
  86          *                  but not acknowledged as completed after this many seconds. Recycling
  87          *                  of jobs simple means re-inserting them into the queue. Jobs can be
  88          *                  attempted up to three times before being discarded.
  89          *   - checkDelay : If supported, respect Job::getReleaseTimestamp() in the push functions.
  90          *                  This lets delayed jobs wait in a staging area until a given timestamp is
  91          *                  reached, at which point they will enter the queue. If this is not enabled
  92          *                  or not supported, an exception will be thrown on delayed job insertion.
  93          *
  94          * Queue classes should throw an exception if they do not support the options given.
  95          *
  96          * @param $params array
  97          * @return JobQueue
  98          * @throws MWException
  99          */
 100         final public static function factory( array $params ) {
 101                 $class = $params['class'];
 102                 if ( !class_exists( $class ) ) {
 103                         throw new MWException( "Invalid job queue class '$class'." );
 104                 }
 105                 $obj = new $class( $params );
 106                 if ( !( $obj instanceof self ) ) {
 107                         throw new MWException( "Class '$class' is not a " . __CLASS__ . " class." );
 108                 }
 109
 110                 return $obj;
 111         }
 112
 113         /**
 114          * @return string Wiki ID
 115          */
 116         final public function getWiki() {
 117                 return $this->wiki;
 118         }
 119
 120         /**
 121          * @return string Job type that this queue handles
 122          */
 123         final public function getType() {
 124                 return $this->type;
 125         }
 126
 127         /**
 128          * @return string One of (random, timestamp, fifo, undefined)
 129          */
 130         final public function getOrder() {
 131                 return $this->order;
 132         }
 133
 134         /**
 135          * @return bool Whether delayed jobs are enabled
 136          * @since 1.22
 137          */
 138         final public function delayedJobsEnabled() {
 139                 return $this->checkDelay;
 140         }
 141
 142         /**
 143          * Get the allowed queue orders for configuration validation
 144          *
 145          * @return Array Subset of (random, timestamp, fifo, undefined)
 146          */
 147         abstract protected function supportedOrders();
 148
 149         /**
 150          * Get the default queue order to use if configuration does not specify one
 151          *
 152          * @return string One of (random, timestamp, fifo, undefined)
 153          */
 154         abstract protected function optimalOrder();
 155
 156         /**
 157          * Find out if delayed jobs are supported for configuration validation
 158          *
 159          * @return boolean Whether delayed jobs are supported
 160          */
 161         protected function supportsDelayedJobs() {
 162                 return false; // not implemented
 163         }
 164
 165         /**
 166          * Quickly check if the queue has no available (unacquired, non-delayed) jobs.
 167          * Queue classes should use caching if they are any slower without memcached.
 168          *
 169          * If caching is used, this might return false when there are actually no jobs.
 170          * If pop() is called and returns false then it should correct the cache. Also,
 171          * calling flushCaches() first prevents this. However, this affect is typically
 172          * not distinguishable from the race condition between isEmpty() and pop().
 173          *
 174          * @return bool
 175          * @throws JobQueueError
 176          */
 177         final public function isEmpty() {
 178                 wfProfileIn( __METHOD__ );
 179                 $res = $this->doIsEmpty();
 180                 wfProfileOut( __METHOD__ );
 181
 182                 return $res;
 183         }
 184
 185         /**
 186          * @see JobQueue::isEmpty()
 187          * @return bool
 188          */
 189         abstract protected function doIsEmpty();
 190
 191         /**
 192          * Get the number of available (unacquired, non-delayed) jobs in the queue.
 193          * Queue classes should use caching if they are any slower without memcached.
 194          *
 195          * If caching is used, this number might be out of date for a minute.
 196          *
 197          * @return integer
 198          * @throws JobQueueError
 199          */
 200         final public function getSize() {
 201                 wfProfileIn( __METHOD__ );
 202                 $res = $this->doGetSize();
 203                 wfProfileOut( __METHOD__ );
 204
 205                 return $res;
 206         }
 207
 208         /**
 209          * @see JobQueue::getSize()
 210          * @return integer
 211          */
 212         abstract protected function doGetSize();
 213
 214         /**
 215          * Get the number of acquired jobs (these are temporarily out of the queue).
 216          * Queue classes should use caching if they are any slower without memcached.
 217          *
 218          * If caching is used, this number might be out of date for a minute.
 219          *
 220          * @return integer
 221          * @throws JobQueueError
 222          */
 223         final public function getAcquiredCount() {
 224                 wfProfileIn( __METHOD__ );
 225                 $res = $this->doGetAcquiredCount();
 226                 wfProfileOut( __METHOD__ );
 227
 228                 return $res;
 229         }
 230
 231         /**
 232          * @see JobQueue::getAcquiredCount()
 233          * @return integer
 234          */
 235         abstract protected function doGetAcquiredCount();
 236
 237         /**
 238          * Get the number of delayed jobs (these are temporarily out of the queue).
 239          * Queue classes should use caching if they are any slower without memcached.
 240          *
 241          * If caching is used, this number might be out of date for a minute.
 242          *
 243          * @return integer
 244          * @throws JobQueueError
 245          * @since 1.22
 246          */
 247         final public function getDelayedCount() {
 248                 wfProfileIn( __METHOD__ );
 249                 $res = $this->doGetDelayedCount();
 250                 wfProfileOut( __METHOD__ );
 251
 252                 return $res;
 253         }
 254
 255         /**
 256          * @see JobQueue::getDelayedCount()
 257          * @return integer
 258          */
 259         protected function doGetDelayedCount() {
 260                 return 0; // not implemented
 261         }
 262
 263         /**
 264          * Get the number of acquired jobs that can no longer be attempted.
 265          * Queue classes should use caching if they are any slower without memcached.
 266          *
 267          * If caching is used, this number might be out of date for a minute.
 268          *
 269          * @return integer
 270          * @throws JobQueueError
 271          */
 272         final public function getAbandonedCount() {
 273                 wfProfileIn( __METHOD__ );
 274                 $res = $this->doGetAbandonedCount();
 275                 wfProfileOut( __METHOD__ );
 276
 277                 return $res;
 278         }
 279
 280         /**
 281          * @see JobQueue::getAbandonedCount()
 282          * @return integer
 283          */
 284         protected function doGetAbandonedCount() {
 285                 return 0; // not implemented
 286         }
 287
 288         /**
 289          * Push a single jobs into the queue.
 290          * This does not require $wgJobClasses to be set for the given job type.
 291          * Outside callers should use JobQueueGroup::push() instead of this function.
 292          *
 293          * @param $jobs Job|Array
 294          * @param $flags integer Bitfield (supports JobQueue::QOS_ATOMIC)
 295          * @return bool Returns false on failure
 296          * @throws JobQueueError
 297          */
 298         final public function push( $jobs, $flags = 0 ) {
 299                 return $this->batchPush( is_array( $jobs ) ? $jobs : array( $jobs ), $flags );
 300         }
 301
 302         /**
 303          * Push a batch of jobs into the queue.
 304          * This does not require $wgJobClasses to be set for the given job type.
 305          * Outside callers should use JobQueueGroup::push() instead of this function.
 306          *
 307          * @param array $jobs List of Jobs
 308          * @param $flags integer Bitfield (supports JobQueue::QOS_ATOMIC)
 309          * @return bool Returns false on failure
 310          * @throws JobQueueError
 311          */
 312         final public function batchPush( array $jobs, $flags = 0 ) {
 313                 if ( !count( $jobs ) ) {
 314                         return true; // nothing to do
 315                 }
 316
 317                 foreach ( $jobs as $job ) {
 318                         if ( $job->getType() !== $this->type ) {
 319                                 throw new MWException(
 320                                         "Got '{$job->getType()}' job; expected a '{$this->type}' job." );
 321                         } elseif ( $job->getReleaseTimestamp() && !$this->checkDelay ) {
 322                                 throw new MWException(
 323                                         "Got delayed '{$job->getType()}' job; delays are not supported." );
 324                         }
 325                 }
 326
 327                 wfProfileIn( __METHOD__ );
 328                 $ok = $this->doBatchPush( $jobs, $flags );
 329                 wfProfileOut( __METHOD__ );
 330
 331                 return $ok;
 332         }
 333
 334         /**
 335          * @see JobQueue::batchPush()
 336          * @return bool
 337          */
 338         abstract protected function doBatchPush( array $jobs, $flags );
 339
 340         /**
 341          * Pop a job off of the queue.
 342          * This requires $wgJobClasses to be set for the given job type.
 343          * Outside callers should use JobQueueGroup::pop() instead of this function.
 344          *
 345          * @return Job|bool Returns false if there are no jobs
 346          * @throws JobQueueError
 347          */
 348         final public function pop() {
 349                 global $wgJobClasses;
 350
 351                 if ( $this->wiki !== wfWikiID() ) {
 352                         throw new MWException( "Cannot pop '{$this->type}' job off foreign wiki queue." );
 353                 } elseif ( !isset( $wgJobClasses[$this->type] ) ) {
 354                         // Do not pop jobs if there is no class for the queue type
 355                         throw new MWException( "Unrecognized job type '{$this->type}'." );
 356                 }
 357
 358                 wfProfileIn( __METHOD__ );
 359                 $job = $this->doPop();
 360                 wfProfileOut( __METHOD__ );
 361
 362                 // Flag this job as an old duplicate based on its "root" job...
 363                 try {
 364                         if ( $job && $this->isRootJobOldDuplicate( $job ) ) {
 365                                 JobQueue::incrStats( 'job-pop-duplicate', $this->type );
 366                                 $job = DuplicateJob::newFromJob( $job ); // convert to a no-op
 367                         }
 368                 } catch ( MWException $e ) {
 369                         // don't lose jobs over this
 370                 }
 371
 372                 return $job;
 373         }
 374
 375         /**
 376          * @see JobQueue::pop()
 377          * @return Job
 378          */
 379         abstract protected function doPop();
 380
 381         /**
 382          * Acknowledge that a job was completed.
 383          *
 384          * This does nothing for certain queue classes or if "claimTTL" is not set.
 385          * Outside callers should use JobQueueGroup::ack() instead of this function.
 386          *
 387          * @param $job Job
 388          * @return bool
 389          * @throws JobQueueError
 390          */
 391         final public function ack( Job $job ) {
 392                 if ( $job->getType() !== $this->type ) {
 393                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 394                 }
 395                 wfProfileIn( __METHOD__ );
 396                 $ok = $this->doAck( $job );
 397                 wfProfileOut( __METHOD__ );
 398
 399                 return $ok;
 400         }
 401
 402         /**
 403          * @see JobQueue::ack()
 404          * @return bool
 405          */
 406         abstract protected function doAck( Job $job );
 407
 408         /**
 409          * Register the "root job" of a given job into the queue for de-duplication.
 410          * This should only be called right *after* all the new jobs have been inserted.
 411          * This is used to turn older, duplicate, job entries into no-ops. The root job
 412          * information will remain in the registry until it simply falls out of cache.
 413          *
 414          * This requires that $job has two special fields in the "params" array:
 415          *   - rootJobSignature : hash (e.g. SHA1) that identifies the task
 416          *   - rootJobTimestamp : TS_MW timestamp of this instance of the task
 417          *
 418          * A "root job" is a conceptual job that consist of potentially many smaller jobs
 419          * that are actually inserted into the queue. For example, "refreshLinks" jobs are
 420          * spawned when a template is edited. One can think of the task as "update links
 421          * of pages that use template X" and an instance of that task as a "root job".
 422          * However, what actually goes into the queue are potentially many refreshLinks2 jobs.
 423          * Since these jobs include things like page ID ranges and DB master positions, and morph
 424          * into smaller refreshLinks2 jobs recursively, simple duplicate detection (like job_sha1)
 425          * for individual jobs being identical is not useful.
 426          *
 427          * In the case of "refreshLinks", if these jobs are still in the queue when the template
 428          * is edited again, we want all of these old refreshLinks jobs for that template to become
 429          * no-ops. This can greatly reduce server load, since refreshLinks jobs involves parsing.
 430          * Essentially, the new batch of jobs belong to a new "root job" and the older ones to a
 431          * previous "root job" for the same task of "update links of pages that use template X".
 432          *
 433          * This does nothing for certain queue classes.
 434          *
 435          * @param $job Job
 436          * @return bool
 437          * @throws JobQueueError
 438          */
 439         final public function deduplicateRootJob( Job $job ) {
 440                 if ( $job->getType() !== $this->type ) {
 441                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 442                 }
 443                 wfProfileIn( __METHOD__ );
 444                 $ok = $this->doDeduplicateRootJob( $job );
 445                 wfProfileOut( __METHOD__ );
 446
 447                 return $ok;
 448         }
 449
 450         /**
 451          * @see JobQueue::deduplicateRootJob()
 452          * @param $job Job
 453          * @return bool
 454          */
 455         protected function doDeduplicateRootJob( Job $job ) {
 456                 if ( !$job->hasRootJobParams() ) {
 457                         throw new MWException( "Cannot register root job; missing parameters." );
 458                 }
 459                 $params = $job->getRootJobParams();
 460
 461                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 462                 // Callers should call batchInsert() and then this function so that if the insert
 463                 // fails, the de-duplication registration will be aborted. Since the insert is
 464                 // deferred till "transaction idle", do the same here, so that the ordering is
 465                 // maintained. Having only the de-duplication registration succeed would cause
 466                 // jobs to become no-ops without any actual jobs that made them redundant.
 467                 $timestamp = $this->dupCache->get( $key ); // current last timestamp of this job
 468                 if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 469                         return true; // a newer version of this root job was enqueued
 470                 }
 471
 472                 // Update the timestamp of the last root job started at the location...
 473                 return $this->dupCache->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
 474         }
 475
 476         /**
 477          * Check if the "root" job of a given job has been superseded by a newer one
 478          *
 479          * @param $job Job
 480          * @return bool
 481          * @throws JobQueueError
 482          */
 483         final protected function isRootJobOldDuplicate( Job $job ) {
 484                 if ( $job->getType() !== $this->type ) {
 485                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 486                 }
 487                 wfProfileIn( __METHOD__ );
 488                 $isDuplicate = $this->doIsRootJobOldDuplicate( $job );
 489                 wfProfileOut( __METHOD__ );
 490
 491                 return $isDuplicate;
 492         }
 493
 494         /**
 495          * @see JobQueue::isRootJobOldDuplicate()
 496          * @param Job $job
 497          * @return bool
 498          */
 499         protected function doIsRootJobOldDuplicate( Job $job ) {
 500                 if ( !$job->hasRootJobParams() ) {
 501                         return false; // job has no de-deplication info
 502                 }
 503                 $params = $job->getRootJobParams();
 504
 505                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 506                 // Get the last time this root job was enqueued
 507                 $timestamp = $this->dupCache->get( $key );
 508
 509                 // Check if a new root job was started at the location after this one's...
 510                 return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
 511         }
 512
 513         /**
 514          * @param string $signature Hash identifier of the root job
 515          * @return string
 516          */
 517         protected function getRootJobCacheKey( $signature ) {
 518                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 519
 520                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
 521         }
 522
 523         /**
 524          * Deleted all unclaimed and delayed jobs from the queue
 525          *
 526          * @return bool Success
 527          * @throws JobQueueError
 528          * @since 1.22
 529          */
 530         final public function delete() {
 531                 wfProfileIn( __METHOD__ );
 532                 $res = $this->doDelete();
 533                 wfProfileOut( __METHOD__ );
 534
 535                 return $res;
 536         }
 537
 538         /**
 539          * @see JobQueue::delete()
 540          * @return bool Success
 541          */
 542         protected function doDelete() {
 543                 throw new MWException( "This method is not implemented." );
 544         }
 545
 546         /**
 547          * Wait for any slaves or backup servers to catch up.
 548          *
 549          * This does nothing for certain queue classes.
 550          *
 551          * @return void
 552          * @throws JobQueueError
 553          */
 554         final public function waitForBackups() {
 555                 wfProfileIn( __METHOD__ );
 556                 $this->doWaitForBackups();
 557                 wfProfileOut( __METHOD__ );
 558         }
 559
 560         /**
 561          * @see JobQueue::waitForBackups()
 562          * @return void
 563          */
 564         protected function doWaitForBackups() {
 565         }
 566
 567         /**
 568          * Return a map of task names to task definition maps.
 569          * A "task" is a fast periodic queue maintenance action.
 570          * Mutually exclusive tasks must implement their own locking in the callback.
 571          *
 572          * Each task value is an associative array with:
 573          *   - name     : the name of the task
 574          *   - callback : a PHP callable that performs the task
 575          *   - period   : the period in seconds corresponding to the task frequency
 576          *
 577          * @return Array
 578          */
 579         final public function getPeriodicTasks() {
 580                 $tasks = $this->doGetPeriodicTasks();
 581                 foreach ( $tasks as $name => &$def ) {
 582                         $def['name'] = $name;
 583                 }
 584
 585                 return $tasks;
 586         }
 587
 588         /**
 589          * @see JobQueue::getPeriodicTasks()
 590          * @return Array
 591          */
 592         protected function doGetPeriodicTasks() {
 593                 return array();
 594         }
 595
 596         /**
 597          * Clear any process and persistent caches
 598          *
 599          * @return void
 600          */
 601         final public function flushCaches() {
 602                 wfProfileIn( __METHOD__ );
 603                 $this->doFlushCaches();
 604                 wfProfileOut( __METHOD__ );
 605         }
 606
 607         /**
 608          * @see JobQueue::flushCaches()
 609          * @return void
 610          */
 611         protected function doFlushCaches() {
 612         }
 613
 614         /**
 615          * Get an iterator to traverse over all available jobs in this queue.
 616          * This does not include jobs that are currently acquired or delayed.
 617          * Note: results may be stale if the queue is concurrently modified.
 618          *
 619          * @return Iterator
 620          * @throws JobQueueError
 621          */
 622         abstract public function getAllQueuedJobs();
 623
 624         /**
 625          * Get an iterator to traverse over all delayed jobs in this queue.
 626          * Note: results may be stale if the queue is concurrently modified.
 627          *
 628          * @return Iterator
 629          * @throws JobQueueError
 630          * @since 1.22
 631          */
 632         public function getAllDelayedJobs() {
 633                 return new ArrayIterator( array() ); // not implemented
 634         }
 635
 636         /**
 637          * Do not use this function outside of JobQueue/JobQueueGroup
 638          *
 639          * @return string
 640          * @since 1.22
 641          */
 642         public function getCoalesceLocationInternal() {
 643                 return null;
 644         }
 645
 646         /**
 647          * Check whether each of the given queues are empty.
 648          * This is used for batching checks for queues stored at the same place.
 649          *
 650          * @param array $types List of queues types
 651          * @return array|null (list of non-empty queue types) or null if unsupported
 652          * @throws MWException
 653          * @since 1.22
 654          */
 655         final public function getSiblingQueuesWithJobs( array $types ) {
 656                 $section = new ProfileSection( __METHOD__ );
 657
 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                 $section = new ProfileSection( __METHOD__ );
 682
 683                 return $this->doGetSiblingQueueSizes( $types );
 684         }
 685
 686         /**
 687          * @see JobQueue::getSiblingQueuesSize()
 688          * @param array $types List of queues types
 689          * @return array|null (list of queue types) or null if unsupported
 690          */
 691         protected function doGetSiblingQueueSizes( array $types ) {
 692                 return null; // not supported
 693         }
 694
 695         /**
 696          * Call wfIncrStats() for the queue overall and for the queue type
 697          *
 698          * @param string $key Event type
 699          * @param string $type Job type
 700          * @param integer $delta
 701          * @since 1.22
 702          */
 703         public static function incrStats( $key, $type, $delta = 1 ) {
 704                 wfIncrStats( $key, $delta );
 705                 wfIncrStats( "{$key}-{$type}", $delta );
 706         }
 707
 708         /**
 709          * Namespace the queue with a key to isolate it for testing
 710          *
 711          * @param $key string
 712          * @return void
 713          * @throws MWException
 714          */
 715         public function setTestingPrefix( $key ) {
 716                 throw new MWException( "Queue namespacing not supported for this queue type." );
 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 }