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