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                 return $obj;
 110         }
 111
 112         /**
 113          * @return string Wiki ID
 114          */
 115         final public function getWiki() {
 116                 return $this->wiki;
 117         }
 118
 119         /**
 120          * @return string Job type that this queue handles
 121          */
 122         final public function getType() {
 123                 return $this->type;
 124         }
 125
 126         /**
 127          * @return string One of (random, timestamp, fifo, undefined)
 128          */
 129         final public function getOrder() {
 130                 return $this->order;
 131         }
 132
 133         /**
 134          * @return bool Whether delayed jobs are enabled
 135          * @since 1.22
 136          */
 137         final public function delayedJobsEnabled() {
 138                 return $this->checkDelay;
 139         }
 140
 141         /**
 142          * Get the allowed queue orders for configuration validation
 143          *
 144          * @return Array Subset of (random, timestamp, fifo, undefined)
 145          */
 146         abstract protected function supportedOrders();
 147
 148         /**
 149          * Get the default queue order to use if configuration does not specify one
 150          *
 151          * @return string One of (random, timestamp, fifo, undefined)
 152          */
 153         abstract protected function optimalOrder();
 154
 155         /**
 156          * Find out if delayed jobs are supported for configuration validation
 157          *
 158          * @return boolean Whether delayed jobs are supported
 159          */
 160         protected function supportsDelayedJobs() {
 161                 return false; // not implemented
 162         }
 163
 164         /**
 165          * Quickly check if the queue has no available (unacquired, non-delayed) jobs.
 166          * Queue classes should use caching if they are any slower without memcached.
 167          *
 168          * If caching is used, this might return false when there are actually no jobs.
 169          * If pop() is called and returns false then it should correct the cache. Also,
 170          * calling flushCaches() first prevents this. However, this affect is typically
 171          * not distinguishable from the race condition between isEmpty() and pop().
 172          *
 173          * @return bool
 174          * @throws JobQueueError
 175          */
 176         final public function isEmpty() {
 177                 wfProfileIn( __METHOD__ );
 178                 $res = $this->doIsEmpty();
 179                 wfProfileOut( __METHOD__ );
 180                 return $res;
 181         }
 182
 183         /**
 184          * @see JobQueue::isEmpty()
 185          * @return bool
 186          */
 187         abstract protected function doIsEmpty();
 188
 189         /**
 190          * Get the number of available (unacquired, non-delayed) jobs in the queue.
 191          * Queue classes should use caching if they are any slower without memcached.
 192          *
 193          * If caching is used, this number might be out of date for a minute.
 194          *
 195          * @return integer
 196          * @throws JobQueueError
 197          */
 198         final public function getSize() {
 199                 wfProfileIn( __METHOD__ );
 200                 $res = $this->doGetSize();
 201                 wfProfileOut( __METHOD__ );
 202                 return $res;
 203         }
 204
 205         /**
 206          * @see JobQueue::getSize()
 207          * @return integer
 208          */
 209         abstract protected function doGetSize();
 210
 211         /**
 212          * Get the number of acquired jobs (these are temporarily out of the queue).
 213          * Queue classes should use caching if they are any slower without memcached.
 214          *
 215          * If caching is used, this number might be out of date for a minute.
 216          *
 217          * @return integer
 218          * @throws JobQueueError
 219          */
 220         final public function getAcquiredCount() {
 221                 wfProfileIn( __METHOD__ );
 222                 $res = $this->doGetAcquiredCount();
 223                 wfProfileOut( __METHOD__ );
 224                 return $res;
 225         }
 226
 227         /**
 228          * @see JobQueue::getAcquiredCount()
 229          * @return integer
 230          */
 231         abstract protected function doGetAcquiredCount();
 232
 233         /**
 234          * Get the number of delayed jobs (these are temporarily out of the queue).
 235          * Queue classes should use caching if they are any slower without memcached.
 236          *
 237          * If caching is used, this number might be out of date for a minute.
 238          *
 239          * @return integer
 240          * @throws JobQueueError
 241          * @since 1.22
 242          */
 243         final public function getDelayedCount() {
 244                 wfProfileIn( __METHOD__ );
 245                 $res = $this->doGetDelayedCount();
 246                 wfProfileOut( __METHOD__ );
 247                 return $res;
 248         }
 249
 250         /**
 251          * @see JobQueue::getDelayedCount()
 252          * @return integer
 253          */
 254         protected function doGetDelayedCount() {
 255                 return 0; // not implemented
 256         }
 257
 258         /**
 259          * Get the number of acquired jobs that can no longer be attempted.
 260          * Queue classes should use caching if they are any slower without memcached.
 261          *
 262          * If caching is used, this number might be out of date for a minute.
 263          *
 264          * @return integer
 265          * @throws JobQueueError
 266          */
 267         final public function getAbandonedCount() {
 268                 wfProfileIn( __METHOD__ );
 269                 $res = $this->doGetAbandonedCount();
 270                 wfProfileOut( __METHOD__ );
 271                 return $res;
 272         }
 273
 274         /**
 275          * @see JobQueue::getAbandonedCount()
 276          * @return integer
 277          */
 278         protected function doGetAbandonedCount() {
 279                 return 0; // not implemented
 280         }
 281
 282         /**
 283          * Push a single jobs into the queue.
 284          * This does not require $wgJobClasses to be set for the given job type.
 285          * Outside callers should use JobQueueGroup::push() instead of this function.
 286          *
 287          * @param $jobs Job|Array
 288          * @param $flags integer Bitfield (supports JobQueue::QOS_ATOMIC)
 289          * @return bool Returns false on failure
 290          * @throws JobQueueError
 291          */
 292         final public function push( $jobs, $flags = 0 ) {
 293                 return $this->batchPush( is_array( $jobs ) ? $jobs : array( $jobs ), $flags );
 294         }
 295
 296         /**
 297          * Push a batch of jobs into the queue.
 298          * This does not require $wgJobClasses to be set for the given job type.
 299          * Outside callers should use JobQueueGroup::push() instead of this function.
 300          *
 301          * @param array $jobs List of Jobs
 302          * @param $flags integer Bitfield (supports JobQueue::QOS_ATOMIC)
 303          * @return bool Returns false on failure
 304          * @throws JobQueueError
 305          */
 306         final public function batchPush( array $jobs, $flags = 0 ) {
 307                 if ( !count( $jobs ) ) {
 308                         return true; // nothing to do
 309                 }
 310
 311                 foreach ( $jobs as $job ) {
 312                         if ( $job->getType() !== $this->type ) {
 313                                 throw new MWException(
 314                                         "Got '{$job->getType()}' job; expected a '{$this->type}' job." );
 315                         } elseif ( $job->getReleaseTimestamp() && !$this->checkDelay ) {
 316                                 throw new MWException(
 317                                         "Got delayed '{$job->getType()}' job; delays are not supported." );
 318                         }
 319                 }
 320
 321                 wfProfileIn( __METHOD__ );
 322                 $ok = $this->doBatchPush( $jobs, $flags );
 323                 wfProfileOut( __METHOD__ );
 324                 return $ok;
 325         }
 326
 327         /**
 328          * @see JobQueue::batchPush()
 329          * @return bool
 330          */
 331         abstract protected function doBatchPush( array $jobs, $flags );
 332
 333         /**
 334          * Pop a job off of the queue.
 335          * This requires $wgJobClasses to be set for the given job type.
 336          * Outside callers should use JobQueueGroup::pop() instead of this function.
 337          *
 338          * @return Job|bool Returns false if there are no jobs
 339          * @throws JobQueueError
 340          */
 341         final public function pop() {
 342                 global $wgJobClasses;
 343
 344                 if ( $this->wiki !== wfWikiID() ) {
 345                         throw new MWException( "Cannot pop '{$this->type}' job off foreign wiki queue." );
 346                 } elseif ( !isset( $wgJobClasses[$this->type] ) ) {
 347                         // Do not pop jobs if there is no class for the queue type
 348                         throw new MWException( "Unrecognized job type '{$this->type}'." );
 349                 }
 350
 351                 wfProfileIn( __METHOD__ );
 352                 $job = $this->doPop();
 353                 wfProfileOut( __METHOD__ );
 354
 355                 // Flag this job as an old duplicate based on its "root" job...
 356                 try {
 357                         if ( $job && $this->isRootJobOldDuplicate( $job ) ) {
 358                                 JobQueue::incrStats( 'job-pop-duplicate', $this->type );
 359                                 $job = DuplicateJob::newFromJob( $job ); // convert to a no-op
 360                         }
 361                 } catch ( MWException $e ) {} // don't lose jobs over this
 362
 363                 return $job;
 364         }
 365
 366         /**
 367          * @see JobQueue::pop()
 368          * @return Job
 369          */
 370         abstract protected function doPop();
 371
 372         /**
 373          * Acknowledge that a job was completed.
 374          *
 375          * This does nothing for certain queue classes or if "claimTTL" is not set.
 376          * Outside callers should use JobQueueGroup::ack() instead of this function.
 377          *
 378          * @param $job Job
 379          * @return bool
 380          * @throws JobQueueError
 381          */
 382         final public function ack( Job $job ) {
 383                 if ( $job->getType() !== $this->type ) {
 384                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 385                 }
 386                 wfProfileIn( __METHOD__ );
 387                 $ok = $this->doAck( $job );
 388                 wfProfileOut( __METHOD__ );
 389                 return $ok;
 390         }
 391
 392         /**
 393          * @see JobQueue::ack()
 394          * @return bool
 395          */
 396         abstract protected function doAck( Job $job );
 397
 398         /**
 399          * Register the "root job" of a given job into the queue for de-duplication.
 400          * This should only be called right *after* all the new jobs have been inserted.
 401          * This is used to turn older, duplicate, job entries into no-ops. The root job
 402          * information will remain in the registry until it simply falls out of cache.
 403          *
 404          * This requires that $job has two special fields in the "params" array:
 405          *   - rootJobSignature : hash (e.g. SHA1) that identifies the task
 406          *   - rootJobTimestamp : TS_MW timestamp of this instance of the task
 407          *
 408          * A "root job" is a conceptual job that consist of potentially many smaller jobs
 409          * that are actually inserted into the queue. For example, "refreshLinks" jobs are
 410          * spawned when a template is edited. One can think of the task as "update links
 411          * of pages that use template X" and an instance of that task as a "root job".
 412          * However, what actually goes into the queue are potentially many refreshLinks2 jobs.
 413          * Since these jobs include things like page ID ranges and DB master positions, and morph
 414          * into smaller refreshLinks2 jobs recursively, simple duplicate detection (like job_sha1)
 415          * for individual jobs being identical is not useful.
 416          *
 417          * In the case of "refreshLinks", if these jobs are still in the queue when the template
 418          * is edited again, we want all of these old refreshLinks jobs for that template to become
 419          * no-ops. This can greatly reduce server load, since refreshLinks jobs involves parsing.
 420          * Essentially, the new batch of jobs belong to a new "root job" and the older ones to a
 421          * previous "root job" for the same task of "update links of pages that use template X".
 422          *
 423          * This does nothing for certain queue classes.
 424          *
 425          * @param $job Job
 426          * @return bool
 427          * @throws JobQueueError
 428          */
 429         final public function deduplicateRootJob( Job $job ) {
 430                 if ( $job->getType() !== $this->type ) {
 431                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 432                 }
 433                 wfProfileIn( __METHOD__ );
 434                 $ok = $this->doDeduplicateRootJob( $job );
 435                 wfProfileOut( __METHOD__ );
 436                 return $ok;
 437         }
 438
 439         /**
 440          * @see JobQueue::deduplicateRootJob()
 441          * @param $job Job
 442          * @return bool
 443          */
 444         protected function doDeduplicateRootJob( Job $job ) {
 445                 if ( !$job->hasRootJobParams() ) {
 446                         throw new MWException( "Cannot register root job; missing parameters." );
 447                 }
 448                 $params = $job->getRootJobParams();
 449
 450                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 451                 // Callers should call batchInsert() and then this function so that if the insert
 452                 // fails, the de-duplication registration will be aborted. Since the insert is
 453                 // deferred till "transaction idle", do the same here, so that the ordering is
 454                 // maintained. Having only the de-duplication registration succeed would cause
 455                 // jobs to become no-ops without any actual jobs that made them redundant.
 456                 $timestamp = $this->dupCache->get( $key ); // current last timestamp of this job
 457                 if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 458                         return true; // a newer version of this root job was enqueued
 459                 }
 460
 461                 // Update the timestamp of the last root job started at the location...
 462                 return $this->dupCache->set( $key, $params['rootJobTimestamp'], JobQueueDB::ROOTJOB_TTL );
 463         }
 464
 465         /**
 466          * Check if the "root" job of a given job has been superseded by a newer one
 467          *
 468          * @param $job Job
 469          * @return bool
 470          * @throws JobQueueError
 471          */
 472         final protected function isRootJobOldDuplicate( Job $job ) {
 473                 if ( $job->getType() !== $this->type ) {
 474                         throw new MWException( "Got '{$job->getType()}' job; expected '{$this->type}'." );
 475                 }
 476                 wfProfileIn( __METHOD__ );
 477                 $isDuplicate = $this->doIsRootJobOldDuplicate( $job );
 478                 wfProfileOut( __METHOD__ );
 479                 return $isDuplicate;
 480         }
 481
 482         /**
 483          * @see JobQueue::isRootJobOldDuplicate()
 484          * @param Job $job
 485          * @return bool
 486          */
 487         protected function doIsRootJobOldDuplicate( Job $job ) {
 488                 if ( !$job->hasRootJobParams() ) {
 489                         return false; // job has no de-deplication info
 490                 }
 491                 $params = $job->getRootJobParams();
 492
 493                 $key = $this->getRootJobCacheKey( $params['rootJobSignature'] );
 494                 // Get the last time this root job was enqueued
 495                 $timestamp = $this->dupCache->get( $key );
 496
 497                 // Check if a new root job was started at the location after this one's...
 498                 return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
 499         }
 500
 501         /**
 502          * @param string $signature Hash identifier of the root job
 503          * @return string
 504          */
 505         protected function getRootJobCacheKey( $signature ) {
 506                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 507                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
 508         }
 509
 510         /**
 511          * Deleted all unclaimed and delayed jobs from the queue
 512          *
 513          * @return bool Success
 514          * @throws JobQueueError
 515          * @since 1.22
 516          */
 517         final public function delete() {
 518                 wfProfileIn( __METHOD__ );
 519                 $res = $this->doDelete();
 520                 wfProfileOut( __METHOD__ );
 521                 return $res;
 522         }
 523
 524         /**
 525          * @see JobQueue::delete()
 526          * @return bool Success
 527          */
 528         protected function doDelete() {
 529                 throw new MWException( "This method is not implemented." );
 530         }
 531
 532         /**
 533          * Wait for any slaves or backup servers to catch up.
 534          *
 535          * This does nothing for certain queue classes.
 536          *
 537          * @return void
 538          * @throws JobQueueError
 539          */
 540         final public function waitForBackups() {
 541                 wfProfileIn( __METHOD__ );
 542                 $this->doWaitForBackups();
 543                 wfProfileOut( __METHOD__ );
 544         }
 545
 546         /**
 547          * @see JobQueue::waitForBackups()
 548          * @return void
 549          */
 550         protected function doWaitForBackups() {}
 551
 552         /**
 553          * Return a map of task names to task definition maps.
 554          * A "task" is a fast periodic queue maintenance action.
 555          * Mutually exclusive tasks must implement their own locking in the callback.
 556          *
 557          * Each task value is an associative array with:
 558          *   - name     : the name of the task
 559          *   - callback : a PHP callable that performs the task
 560          *   - period   : the period in seconds corresponding to the task frequency
 561          *
 562          * @return Array
 563          */
 564         final public function getPeriodicTasks() {
 565                 $tasks = $this->doGetPeriodicTasks();
 566                 foreach ( $tasks as $name => &$def ) {
 567                         $def['name'] = $name;
 568                 }
 569                 return $tasks;
 570         }
 571
 572         /**
 573          * @see JobQueue::getPeriodicTasks()
 574          * @return Array
 575          */
 576         protected function doGetPeriodicTasks() {
 577                 return array();
 578         }
 579
 580         /**
 581          * Clear any process and persistent caches
 582          *
 583          * @return void
 584          */
 585         final public function flushCaches() {
 586                 wfProfileIn( __METHOD__ );
 587                 $this->doFlushCaches();
 588                 wfProfileOut( __METHOD__ );
 589         }
 590
 591         /**
 592          * @see JobQueue::flushCaches()
 593          * @return void
 594          */
 595         protected function doFlushCaches() {}
 596
 597         /**
 598          * Get an iterator to traverse over all available jobs in this queue.
 599          * This does not include jobs that are currently acquired or delayed.
 600          * Note: results may be stale if the queue is concurrently modified.
 601          *
 602          * @return Iterator
 603          * @throws JobQueueError
 604          */
 605         abstract public function getAllQueuedJobs();
 606
 607         /**
 608          * Get an iterator to traverse over all delayed jobs in this queue.
 609          * Note: results may be stale if the queue is concurrently modified.
 610          *
 611          * @return Iterator
 612          * @throws JobQueueError
 613          * @since 1.22
 614          */
 615         public function getAllDelayedJobs() {
 616                 return new ArrayIterator( array() ); // not implemented
 617         }
 618
 619         /**
 620          * Do not use this function outside of JobQueue/JobQueueGroup
 621          *
 622          * @return string
 623          * @since 1.22
 624          */
 625         public function getCoalesceLocationInternal() {
 626                 return null;
 627         }
 628
 629         /**
 630          * Check whether each of the given queues are empty.
 631          * This is used for batching checks for queues stored at the same place.
 632          *
 633          * @param array $types List of queues types
 634          * @return array|null (list of non-empty queue types) or null if unsupported
 635          * @throws MWException
 636          * @since 1.22
 637          */
 638         final public function getSiblingQueuesWithJobs( array $types ) {
 639                 $section = new ProfileSection( __METHOD__ );
 640                 return $this->doGetSiblingQueuesWithJobs( $types );
 641         }
 642
 643         /**
 644          * @see JobQueue::getSiblingQueuesWithJobs()
 645          * @param array $types List of queues types
 646          * @return array|null (list of queue types) or null if unsupported
 647          */
 648         protected function doGetSiblingQueuesWithJobs( array $types ) {
 649                 return null; // not supported
 650         }
 651
 652         /**
 653          * Check the size of each of the given queues.
 654          * For queues not served by the same store as this one, 0 is returned.
 655          * This is used for batching checks for queues stored at the same place.
 656          *
 657          * @param array $types List of queues types
 658          * @return array|null (job type => whether queue is empty) or null if unsupported
 659          * @throws MWException
 660          * @since 1.22
 661          */
 662         final public function getSiblingQueueSizes( array $types ) {
 663                 $section = new ProfileSection( __METHOD__ );
 664                 return $this->doGetSiblingQueueSizes( $types );
 665         }
 666
 667         /**
 668          * @see JobQueue::getSiblingQueuesSize()
 669          * @param array $types List of queues types
 670          * @return array|null (list of queue types) or null if unsupported
 671          */
 672         protected function doGetSiblingQueueSizes( array $types ) {
 673                 return null; // not supported
 674         }
 675
 676         /**
 677          * Call wfIncrStats() for the queue overall and for the queue type
 678          *
 679          * @param string $key Event type
 680          * @param string $type Job type
 681          * @param integer $delta
 682          * @since 1.22
 683          */
 684         public static function incrStats( $key, $type, $delta = 1 ) {
 685                 wfIncrStats( $key, $delta );
 686                 wfIncrStats( "{$key}-{$type}", $delta );
 687         }
 688
 689         /**
 690          * Namespace the queue with a key to isolate it for testing
 691          *
 692          * @param $key string
 693          * @return void
 694          * @throws MWException
 695          */
 696         public function setTestingPrefix( $key ) {
 697                 throw new MWException( "Queue namespacing not supported for this queue type." );
 698         }
 699 }
 700
 701 /**
 702  * @ingroup JobQueue
 703  * @since 1.22
 704  */
 705 class JobQueueError extends MWException {}
 706 class JobQueueConnectionError extends JobQueueError {}