includes/job/JobQueueRedis.php

   1 <?php
   2 /**
   3  * Redis-backed job queue 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  * @author Aaron Schulz
  22  */
  23
  24 /**
  25  * Class to handle job queues stored in Redis
  26  *
  27  * @ingroup JobQueue
  28  * @since 1.21
  29  */
  30 class JobQueueRedis extends JobQueue {
  31         /** @var RedisConnectionPool */
  32         protected $redisPool;
  33
  34         protected $server; // string; server address
  35
  36         const ROOTJOB_TTL = 1209600; // integer; seconds to remember root jobs (14 days)
  37         const MAX_AGE_PRUNE = 604800; // integer; seconds a job can live once claimed (7 days)
  38
  39         protected $key; // string; key to prefix the queue keys with (used for testing)
  40
  41         /**
  42          * @params include:
  43          *   - redisConfig : An array of parameters to RedisConnectionPool::__construct().
  44          *   - redisServer : A hostname/port combination or the absolute path of a UNIX socket.
  45          *                   If a hostname is specified but no port, the standard port number
  46          *                   6379 will be used. Required.
  47          * @param array $params
  48          */
  49         public function __construct( array $params ) {
  50                 parent::__construct( $params );
  51                 $this->server = $params['redisServer'];
  52                 $this->redisPool = RedisConnectionPool::singleton( $params['redisConfig'] );
  53         }
  54
  55         public function supportedOrders() {
  56                 return array( 'timestamp', 'fifo' );
  57         }
  58
  59         protected function optimalOrder() {
  60                 return 'fifo';
  61         }
  62
  63         /**
  64          * @see JobQueue::doIsEmpty()
  65          * @return bool
  66          * @throws MWException
  67          */
  68         protected function doIsEmpty() {
  69                 $conn = $this->getConnection();
  70                 try {
  71                         return ( $conn->lSize( $this->getQueueKey( 'l-unclaimed' ) ) == 0 );
  72                 } catch ( RedisException $e ) {
  73                         $this->throwRedisException( $this->server, $conn, $e );
  74                 }
  75         }
  76
  77         /**
  78          * @see JobQueue::doGetSize()
  79          * @return integer
  80          * @throws MWException
  81          */
  82         protected function doGetSize() {
  83                 $conn = $this->getConnection();
  84                 try {
  85                         return $conn->lSize( $this->getQueueKey( 'l-unclaimed' ) );
  86                 } catch ( RedisException $e ) {
  87                         $this->throwRedisException( $this->server, $conn, $e );
  88                 }
  89         }
  90
  91         /**
  92          * @see JobQueue::doGetAcquiredCount()
  93          * @return integer
  94          * @throws MWException
  95          */
  96         protected function doGetAcquiredCount() {
  97                 if ( $this->claimTTL <= 0 ) {
  98                         return 0; // no acknowledgements
  99                 }
 100                 $conn = $this->getConnection();
 101                 try {
 102                         return $conn->lSize( $this->getQueueKey( 'l-claimed' ) );
 103                 } catch ( RedisException $e ) {
 104                         $this->throwRedisException( $this->server, $conn, $e );
 105                 }
 106         }
 107
 108         /**
 109          * @see JobQueue::doBatchPush()
 110          * @param array $jobs
 111          * @param $flags
 112          * @return bool
 113          * @throws MWException
 114          */
 115         protected function doBatchPush( array $jobs, $flags ) {
 116                 if ( !count( $jobs ) ) {
 117                         return true;
 118                 }
 119
 120                 // Convert the jobs into a list of field maps
 121                 $items = array(); // (uid => job fields map)
 122                 foreach ( $jobs as $job ) {
 123                         $item = $this->getNewJobFields( $job );
 124                         $items[$item['uid']] = $item;
 125                 }
 126
 127                 $dedupUids = array(); // list of uids to check for duplicates
 128                 foreach ( $items as $item ) {
 129                         if ( $this->isHashUid( $item['uid'] ) ) { // hash identifier => de-duplicate
 130                                 $dedupUids[] = $item['uid'];
 131                         }
 132                 }
 133
 134                 $conn = $this->getConnection();
 135                 try {
 136                         // Find which of these jobs are duplicates of unclaimed jobs in the queue...
 137                         if ( count( $dedupUids ) ) {
 138                                 $conn->multi( Redis::PIPELINE );
 139                                 foreach ( $dedupUids as $uid ) { // check if job data exists
 140                                         $conn->exists( $this->prefixWithQueueKey( 'data', $uid ) );
 141                                 }
 142                                 if ( $this->claimTTL > 0 ) { // check which jobs were claimed
 143                                         foreach ( $dedupUids as $uid ) {
 144                                                 $conn->hExists( $this->prefixWithQueueKey( 'h-meta', $uid ), 'ctime' );
 145                                         }
 146                                         list( $exists, $claimed ) = array_chunk( $conn->exec(), count( $dedupUids ) );
 147                                 } else {
 148                                         $exists = $conn->exec();
 149                                         $claimed = array(); // no claim system
 150                                 }
 151                                 // Remove the duplicate jobs to cut down on pushing duplicate uids...
 152                                 foreach ( $dedupUids as $k => $uid ) {
 153                                         if ( $exists[$k] && empty( $claimed[$k] ) ) {
 154                                                 unset( $items[$uid] );
 155                                         }
 156                                 }
 157                         }
 158                         // Actually push the non-duplicate jobs into the queue...
 159                         if ( count( $items ) ) {
 160                                 $uids = array_keys( $items );
 161                                 $conn->multi( Redis::MULTI ); // begin (atomic trx)
 162                                 $conn->mSet( $this->prefixKeysWithQueueKey( 'data', $items ) );
 163                                 call_user_func_array(
 164                                         array( $conn, 'lPush' ),
 165                                         array_merge( array( $this->getQueueKey( 'l-unclaimed' ) ), $uids )
 166                                 );
 167                                 $res = $conn->exec(); // commit (atomic trx)
 168                                 if ( in_array( false, $res, true ) ) {
 169                                         wfDebugLog( 'JobQueueRedis', "Could not insert {$this->type} job(s)." );
 170                                         return false;
 171                                 }
 172                         }
 173                         wfIncrStats( 'job-insert', count( $items ) );
 174                         wfIncrStats( 'job-insert-duplicate', count( $jobs ) - count( $items ) );
 175                 } catch ( RedisException $e ) {
 176                         $this->throwRedisException( $this->server, $conn, $e );
 177                 }
 178
 179                 return true;
 180         }
 181
 182         /**
 183          * @see JobQueue::doPop()
 184          * @return Job|bool
 185          * @throws MWException
 186          */
 187         protected function doPop() {
 188                 $job = false;
 189
 190                 if ( $this->claimTTL <= 0 && mt_rand( 0, 99 ) == 0 ) {
 191                         $this->cleanupClaimedJobs(); // prune jobs and IDs from the "garbage" list
 192                 }
 193
 194                 $conn = $this->getConnection();
 195                 try {
 196                         do {
 197                                 // Atomically pop an item off the queue and onto the "claimed" list
 198                                 $uid = $conn->rpoplpush(
 199                                         $this->getQueueKey( 'l-unclaimed' ),
 200                                         $this->getQueueKey( 'l-claimed' )
 201                                 );
 202                                 if ( $uid === false ) {
 203                                         break; // no jobs; nothing to do
 204                                 }
 205
 206                                 wfIncrStats( 'job-pop' );
 207                                 $conn->multi( Redis::PIPELINE );
 208                                 $conn->get( $this->prefixWithQueueKey( 'data', $uid ) );
 209                                 if ( $this->claimTTL > 0 ) {
 210                                         // Set the claim timestamp metadata. If this step fails, then
 211                                         // the timestamp will be assumed to be the current timestamp by
 212                                         // recycleAndDeleteStaleJobs() as of the next time that it runs.
 213                                         // If two runners claim duplicate jobs, one will abort here.
 214                                         $conn->hSetNx( $this->prefixWithQueueKey( 'h-meta', $uid ), 'ctime', time() );
 215                                 } else {
 216                                         // If this fails, the message key will be deleted in cleanupClaimedJobs().
 217                                         // If two runners claim duplicate jobs, one of them will abort here.
 218                                         $conn->delete(
 219                                                 $this->prefixWithQueueKey( 'h-meta', $uid ),
 220                                                 $this->prefixWithQueueKey( 'data', $uid ) );
 221                                 }
 222                                 list( $item, $ok ) = $conn->exec();
 223                                 if ( $item === false || ( $this->claimTTL && !$ok ) ) {
 224                                         wfDebug( "Could not find or delete job $uid; probably was a duplicate." );
 225                                         continue; // job was probably a duplicate
 226                                 }
 227
 228                                 // If $item is invalid, recycleAndDeleteStaleJobs() will cleanup as needed
 229                                 $job = $this->getJobFromFields( $item ); // may be false
 230                         } while ( !$job ); // job may be false if invalid
 231                 } catch ( RedisException $e ) {
 232                         $this->throwRedisException( $this->server, $conn, $e );
 233                 }
 234
 235                 // Flag this job as an old duplicate based on its "root" job...
 236                 try {
 237                         if ( $job && $this->isRootJobOldDuplicate( $job ) ) {
 238                                 wfIncrStats( 'job-pop-duplicate' );
 239                                 return DuplicateJob::newFromJob( $job ); // convert to a no-op
 240                         }
 241                 } catch ( MWException $e ) {} // don't lose jobs over this
 242
 243                 return $job;
 244         }
 245
 246         /**
 247          * @see JobQueue::doAck()
 248          * @param Job $job
 249          * @return Job|bool
 250          * @throws MWException
 251          */
 252         protected function doAck( Job $job ) {
 253                 if ( $this->claimTTL > 0 ) {
 254                         $conn = $this->getConnection();
 255                         try {
 256                                 // Get the exact field map this Job came from, regardless of whether
 257                                 // the job was transformed into a DuplicateJob or anything of the sort.
 258                                 $item = $job->metadata['sourceFields'];
 259
 260                                 $conn->multi( Redis::MULTI ); // begin (atomic trx)
 261                                 // Remove the first instance of this job scanning right-to-left.
 262                                 // This is O(N) in the worst case, but is likely to be much faster since
 263                                 // jobs are pushed to the left and we are starting from the right, where
 264                                 // the longest running jobs are likely to be. These should be the first
 265                                 // jobs to be acknowledged assuming that job run times are roughly equal.
 266                                 $conn->lRem( $this->getQueueKey( 'l-claimed' ), $item['uid'], -1 );
 267                                 // Delete the job data and its claim metadata
 268                                 $conn->delete(
 269                                         $this->prefixWithQueueKey( 'h-meta', $item['uid'] ),
 270                                         $this->prefixWithQueueKey( 'data', $item['uid'] ) );
 271                                 $res = $conn->exec(); // commit (atomic trx)
 272
 273                                 if ( in_array( false, $res, true ) ) {
 274                                         wfDebugLog( 'JobQueueRedis', "Could not acknowledge {$this->type} job." );
 275                                         return false;
 276                                 }
 277                         } catch ( RedisException $e ) {
 278                                 $this->throwRedisException( $this->server, $conn, $e );
 279                         }
 280                 }
 281                 return true;
 282         }
 283
 284         /**
 285          * @see JobQueue::doDeduplicateRootJob()
 286          * @param Job $job
 287          * @return bool
 288          * @throws MWException
 289          */
 290         protected function doDeduplicateRootJob( Job $job ) {
 291                 $params = $job->getParams();
 292                 if ( !isset( $params['rootJobSignature'] ) ) {
 293                         throw new MWException( "Cannot register root job; missing 'rootJobSignature'." );
 294                 } elseif ( !isset( $params['rootJobTimestamp'] ) ) {
 295                         throw new MWException( "Cannot register root job; missing 'rootJobTimestamp'." );
 296                 }
 297                 $key = $this->getRootJobKey( $params['rootJobSignature'] );
 298
 299                 $conn = $this->getConnection();
 300                 try {
 301                         $timestamp = $conn->get( $key ); // current last timestamp of this job
 302                         if ( $timestamp && $timestamp >= $params['rootJobTimestamp'] ) {
 303                                 return true; // a newer version of this root job was enqueued
 304                         }
 305                         // Update the timestamp of the last root job started at the location...
 306                         return $conn->set( $key, $params['rootJobTimestamp'], self::ROOTJOB_TTL ); // 2 weeks
 307                 } catch ( RedisException $e ) {
 308                         $this->throwRedisException( $this->server, $conn, $e );
 309                 }
 310         }
 311
 312         /**
 313          * Check if the "root" job of a given job has been superseded by a newer one
 314          *
 315          * @param $job Job
 316          * @return bool
 317          * @throws MWException
 318          */
 319         protected function isRootJobOldDuplicate( Job $job ) {
 320                 $params = $job->getParams();
 321                 if ( !isset( $params['rootJobSignature'] ) ) {
 322                         return false; // job has no de-deplication info
 323                 } elseif ( !isset( $params['rootJobTimestamp'] ) ) {
 324                         wfDebugLog( 'JobQueueRedis', "Cannot check root job; missing 'rootJobTimestamp'." );
 325                         return false;
 326                 }
 327
 328                 $conn = $this->getConnection();
 329                 try {
 330                         // Get the last time this root job was enqueued
 331                         $timestamp = $conn->get( $this->getRootJobKey( $params['rootJobSignature'] ) );
 332                 } catch ( RedisException $e ) {
 333                         $this->throwRedisException( $this->server, $conn, $e );
 334                 }
 335
 336                 // Check if a new root job was started at the location after this one's...
 337                 return ( $timestamp && $timestamp > $params['rootJobTimestamp'] );
 338         }
 339
 340         /**
 341          * @see JobQueue::getAllQueuedJobs()
 342          * @return Iterator
 343          */
 344         public function getAllQueuedJobs() {
 345                 $conn = $this->getConnection();
 346                 if ( !$conn ) {
 347                         throw new MWException( "Unable to connect to redis server." );
 348                 }
 349                 try {
 350                         $that = $this;
 351                         return new MappedIterator(
 352                                 $conn->lRange( $this->getQueueKey( 'l-unclaimed' ), 0, -1 ),
 353                                 function( $uid ) use ( $that, $conn ) {
 354                                         return $that->getJobFromUidInternal( $uid, $conn );
 355                                 }
 356                         );
 357                 } catch ( RedisException $e ) {
 358                         $this->throwRedisException( $this->server, $conn, $e );
 359                 }
 360         }
 361
 362         /**
 363          * This function should not be called outside RedisJobQueue
 364          *
 365          * @param $uid string
 366          * @param $conn RedisConnRef
 367          * @return Job
 368          * @throws MWException
 369          */
 370         public function getJobFromUidInternal( $uid, RedisConnRef $conn ) {
 371                 try {
 372                         $fields = $conn->get( $this->prefixWithQueueKey( 'data', $uid ) );
 373                         if ( !is_array( $fields ) ) { // wtf?
 374                                 $conn->delete( $this->prefixWithQueueKey( 'data', $uid ) );
 375                                 throw new MWException( "Could not find job with UID '$uid'." );
 376                         }
 377                         $title = Title::makeTitle( $fields['namespace'], $fields['title'] );
 378                         $job = Job::factory( $fields['type'], $title, $fields['params'] );
 379                         $job->metadata['sourceFields'] = $fields;
 380                         return $job;
 381                 } catch ( RedisException $e ) {
 382                         $this->throwRedisException( $this->server, $conn, $e );
 383                 }
 384         }
 385
 386         /**
 387          * Recycle or destroy any jobs that have been claimed for too long
 388          *
 389          * @return integer Number of jobs recycled/deleted
 390          * @throws MWException
 391          */
 392         public function recycleAndDeleteStaleJobs() {
 393                 if ( $this->claimTTL <= 0 ) { // sanity
 394                         throw new MWException( "Cannot recycle jobs since acknowledgements are disabled." );
 395                 }
 396                 $count = 0;
 397                 // For each job item that can be retried, we need to add it back to the
 398                 // main queue and remove it from the list of currenty claimed job items.
 399                 $conn = $this->getConnection();
 400                 try {
 401                         // Avoid duplicate insertions of items to be re-enqueued
 402                         $conn->multi( Redis::MULTI );
 403                         $conn->setnx( $this->getQueueKey( 'lock' ), 1 );
 404                         $conn->expire( $this->getQueueKey( 'lock' ), 3600 );
 405                         if ( $conn->exec() !== array( true, true ) ) { // lock
 406                                 return $count; // already in progress
 407                         }
 408
 409                         $now = time();
 410                         $claimCutoff = $now - $this->claimTTL;
 411                         $pruneCutoff = $now - self::MAX_AGE_PRUNE;
 412
 413                         // Get the list of all claimed jobs
 414                         $claimedUids = $conn->lRange( $this->getQueueKey( 'l-claimed' ), 0, -1 );
 415                         // Get a map of (uid => claim metadata) for all claimed jobs
 416                         $metadata = $conn->mGet( $this->prefixValuesWithQueueKey( 'h-meta', $claimedUids ) );
 417
 418                         $uidsPush = array(); // items IDs to move to the "unclaimed" queue
 419                         $uidsRemove = array(); // item IDs to remove from "claimed" queue
 420                         foreach ( $claimedUids as $i => $uid ) { // all claimed items
 421                                 $info = $metadata[$i] ? $metadata[$i] : array();
 422                                 if ( isset( $info['ctime'] ) || isset( $info['rctime'] ) ) {
 423                                         // Prefer "ctime" (set by pop()) over "rctime" (set by this function)
 424                                         $ctime = isset( $info['ctime'] ) ? $info['ctime'] : $info['rctime'];
 425                                         // Claimed job claimed for too long?
 426                                         if ( $ctime < $claimCutoff ) {
 427                                                 // Get the number of failed attempts
 428                                                 $attempts = isset( $info['attempts'] ) ? $info['attempts'] : 0;
 429                                                 if ( $attempts < $this->maxTries ) {
 430                                                         $uidsPush[] = $uid; // retry it
 431                                                 } elseif ( $ctime < $pruneCutoff ) {
 432                                                         $uidsRemove[] = $uid; // just remove it
 433                                                 }
 434                                         }
 435                                 } else {
 436                                         // If pop() failed to set the claim timestamp, set it to the current time.
 437                                         // Since that function sets this non-atomically *after* moving the job to
 438                                         // the "claimed" queue, it may be the case that it just didn't set it yet.
 439                                         $conn->hSet( $this->prefixWithQueueKey( 'h-meta', $uid ), 'rctime', $now );
 440                                 }
 441                         }
 442
 443                         $conn->multi( Redis::MULTI ); // begin (atomic trx)
 444                         if ( count( $uidsPush ) ) { // move from "l-claimed" to "l-unclaimed"
 445                                 call_user_func_array(
 446                                         array( $conn, 'lPush' ),
 447                                         array_merge( array( $this->getQueueKey( 'l-unclaimed' ) ), $uidsPush )
 448                                 );
 449                                 foreach ( $uidsPush as $uid ) {
 450                                         $conn->lRem( $this->getQueueKey( 'l-claimed' ), $uid, -1 );
 451                                         $conn->hDel( $this->prefixWithQueueKey( 'h-meta', $uid ), 'ctime', 'rctime' );
 452                                         $conn->hIncrBy( $this->prefixWithQueueKey( 'h-meta', $uid ), 'attempts', 1 );
 453                                 }
 454                         }
 455                         foreach ( $uidsRemove as $uid ) { // remove from "l-claimed"
 456                                 $conn->lRem( $this->getQueueKey( 'l-claimed' ), $uid, -1 );
 457                                 $conn->delete( // delete job data and metadata
 458                                         $this->prefixWithQueueKey( 'h-meta', $uid ),
 459                                         $this->prefixWithQueueKey( 'data', $uid ) );
 460                         }
 461                         $res = $conn->exec(); // commit (atomic trx)
 462
 463                         if ( in_array( false, $res, true ) ) {
 464                                 wfDebugLog( 'JobQueueRedis', "Could not recycle {$this->type} job(s)." );
 465                         } else {
 466                                 $count += ( count( $uidsPush ) + count( $uidsRemove ) );
 467                                 wfIncrStats( 'job-recycle', count( $uidsPush ) );
 468                         }
 469
 470                         $conn->delete( $this->getQueueKey( 'lock' ) ); // unlock
 471                 } catch ( RedisException $e ) {
 472                         $this->throwRedisException( $this->server, $conn, $e );
 473                 }
 474
 475                 return $count;
 476         }
 477
 478         /**
 479          * Destroy any jobs that have been claimed
 480          *
 481          * @return integer Number of jobs deleted
 482          * @throws MWException
 483          */
 484         protected function cleanupClaimedJobs() {
 485                 $count = 0;
 486                 // Make sure the message for claimed jobs was deleted
 487                 // and remove the claimed job IDs from the "claimed" list.
 488                 $conn = $this->getConnection();
 489                 try {
 490                         // Avoid races and duplicate effort
 491                         $conn->multi( Redis::MULTI );
 492                         $conn->setnx( $this->getQueueKey( 'lock' ), 1 );
 493                         $conn->expire( $this->getQueueKey( 'lock' ), 3600 );
 494                         if ( $conn->exec() !== array( true, true ) ) { // lock
 495                                 return $count; // already in progress
 496                         }
 497                         // Get the list of all claimed jobs
 498                         $uids = $conn->lRange( $this->getQueueKey( 'l-claimed' ), 0, -1 );
 499                         if ( count( $uids ) ) {
 500                                 // Delete the message keys and delist the corresponding ids.
 501                                 // Since the only other changes to "l-claimed" are left pushes, we can just strip
 502                                 // off the elements read here using a right trim based on the number of ids read.
 503                                 $conn->multi( Redis::MULTI ); // begin (atomic trx)
 504                                 $conn->lTrim( $this->getQueueKey( 'l-claimed' ), 0, -count( $uids ) - 1 );
 505                                 $conn->delete( array_merge(
 506                                         $this->prefixValuesWithQueueKey( 'h-meta', $uids ),
 507                                         $this->prefixValuesWithQueueKey( 'data', $uids )
 508                                 ) );
 509                                 $res = $conn->exec(); // commit (atomic trx)
 510
 511                                 if ( in_array( false, $res, true ) ) {
 512                                         wfDebugLog( 'JobQueueRedis', "Could not purge {$this->type} job(s)." );
 513                                 } else {
 514                                         $count += count( $uids );
 515                                 }
 516                         }
 517                         $conn->delete( $this->getQueueKey( 'lock' ) ); // unlock
 518                 } catch ( RedisException $e ) {
 519                         $this->throwRedisException( $this->server, $conn, $e );
 520                 }
 521
 522                 return $count;
 523         }
 524
 525         /**
 526          * @return Array
 527          */
 528         protected function doGetPeriodicTasks() {
 529                 if ( $this->claimTTL > 0 ) {
 530                         return array(
 531                                 'recycleAndDeleteStaleJobs' => array(
 532                                         'callback' => array( $this, 'recycleAndDeleteStaleJobs' ),
 533                                         'period'   => ceil( $this->claimTTL / 2 )
 534                                 )
 535                         );
 536                 } else {
 537                         return array();
 538                 }
 539         }
 540
 541         /**
 542          * @param $job Job
 543          * @return array
 544          */
 545         protected function getNewJobFields( Job $job ) {
 546                 return array(
 547                         // Fields that describe the nature of the job
 548                         'type'      => $job->getType(),
 549                         'namespace' => $job->getTitle()->getNamespace(),
 550                         'title'     => $job->getTitle()->getDBkey(),
 551                         'params'    => $job->getParams(),
 552                         // Additional metadata
 553                         'uid'       => $job->ignoreDuplicates()
 554                                 ? wfBaseConvert( sha1( serialize( $job->getDeduplicationInfo() ) ), 16, 36, 31 )
 555                                 : wfRandomString( 32 ),
 556                         'timestamp' => time() // UNIX timestamp
 557                 );
 558         }
 559
 560         /**
 561          * @param $fields array
 562          * @return Job|bool
 563          */
 564         protected function getJobFromFields( array $fields ) {
 565                 $title = Title::makeTitleSafe( $fields['namespace'], $fields['title'] );
 566                 if ( $title ) {
 567                         $job = Job::factory( $fields['type'], $title, $fields['params'] );
 568                         $job->metadata['sourceFields'] = $fields;
 569                         return $job;
 570                 }
 571                 return false;
 572         }
 573
 574         /**
 575          * @param $uid string Job UID
 576          * @return bool Whether $uid is a SHA-1 hash based identifier for de-duplication
 577          */
 578         protected function isHashUid( $uid ) {
 579                 return strlen( $uid ) == 31;
 580         }
 581
 582         /**
 583          * Get a connection to the server that handles all sub-queues for this queue
 584          *
 585          * @return Array (server name, Redis instance)
 586          * @throws MWException
 587          */
 588         protected function getConnection() {
 589                 $conn = $this->redisPool->getConnection( $this->server );
 590                 if ( !$conn ) {
 591                         throw new MWException( "Unable to connect to redis server." );
 592                 }
 593                 return $conn;
 594         }
 595
 596         /**
 597          * @param $server string
 598          * @param $conn RedisConnRef
 599          * @param $e RedisException
 600          * @throws MWException
 601          */
 602         protected function throwRedisException( $server, RedisConnRef $conn, $e ) {
 603                 $this->redisPool->handleException( $server, $conn, $e );
 604                 throw new MWException( "Redis server error: {$e->getMessage()}\n" );
 605         }
 606
 607         /**
 608          * @param $prop string
 609          * @return string
 610          */
 611         private function getQueueKey( $prop ) {
 612                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 613                 if ( strlen( $this->key ) ) { // namespaced queue (for testing)
 614                         return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, $this->key, $prop );
 615                 } else {
 616                         return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, $prop );
 617                 }
 618         }
 619
 620         /**
 621          * @param string $signature Hash identifier of the root job
 622          * @return string
 623          */
 624         private function getRootJobKey( $signature ) {
 625                 list( $db, $prefix ) = wfSplitWikiID( $this->wiki );
 626                 return wfForeignMemcKey( $db, $prefix, 'jobqueue', $this->type, 'rootjob', $signature );
 627         }
 628
 629         /**
 630          * @param $prop string
 631          * @param $string string
 632          * @return string
 633          */
 634         private function prefixWithQueueKey( $prop, $string ) {
 635                 return $this->getQueueKey( $prop ) . ':' . $string;
 636         }
 637
 638         /**
 639          * @param $prop string
 640          * @param $items array
 641          * @return Array
 642          */
 643         private function prefixValuesWithQueueKey( $prop, array $items ) {
 644                 $res = array();
 645                 foreach ( $items as $item ) {
 646                         $res[] = $this->prefixWithQueueKey( $prop, $item );
 647                 }
 648                 return $res;
 649         }
 650
 651         /**
 652          * @param $prop string
 653          * @param $items array
 654          * @return Array
 655          */
 656         private function prefixKeysWithQueueKey( $prop, array $items ) {
 657                 $res = array();
 658                 foreach ( $items as $key => $item ) {
 659                         $res[$this->prefixWithQueueKey( $prop, $key )] = $item;
 660                 }
 661                 return $res;
 662         }
 663
 664         /**
 665          * @param $key string
 666          * @return void
 667          */
 668         public function setTestingPrefix( $key ) {
 669                 $this->key = $key;
 670         }
 671 }