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