includes/job/JobQueue.php

   1 <?php
   2 /**
   3  * Job queue base code
   4  *
   5  * @file
   6  * @defgroup JobQueue JobQueue
   7  */
   8
   9 if ( !defined( 'MEDIAWIKI' ) ) {
  10         die( "This file is part of MediaWiki, it is not a valid entry point\n" );
  11 }
  12
  13 /**
  14  * Class to both describe a background job and handle jobs.
  15  *
  16  * @ingroup JobQueue
  17  */
  18 abstract class Job {
  19
  20         /**
  21          * @var Title
  22          */
  23         var $title;
  24
  25         var $command,
  26                 $params,
  27                 $id,
  28                 $removeDuplicates,
  29                 $error;
  30
  31         /*-------------------------------------------------------------------------
  32          * Abstract functions
  33          *------------------------------------------------------------------------*/
  34
  35         /**
  36          * Run the job
  37          * @return boolean success
  38          */
  39         abstract function run();
  40
  41         /*-------------------------------------------------------------------------
  42          * Static functions
  43          *------------------------------------------------------------------------*/
  44
  45         /**
  46          * Pop a job of a certain type.  This tries less hard than pop() to
  47          * actually find a job; it may be adversely affected by concurrent job
  48          * runners.
  49          */
  50         static function pop_type( $type ) {
  51                 wfProfilein( __METHOD__ );
  52
  53                 $dbw = wfGetDB( DB_MASTER );
  54
  55                 $row = $dbw->selectRow(
  56                         'job',
  57                         '*',
  58                         array( 'job_cmd' => $type ),
  59                         __METHOD__,
  60                         array( 'LIMIT' => 1 )
  61                 );
  62
  63                 if ( $row === false ) {
  64                         wfProfileOut( __METHOD__ );
  65                         return false;
  66                 }
  67
  68                 /* Ensure we "own" this row */
  69                 $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
  70                 $affected = $dbw->affectedRows();
  71
  72                 if ( $affected == 0 ) {
  73                         wfProfileOut( __METHOD__ );
  74                         return false;
  75                 }
  76
  77                 $namespace = $row->job_namespace;
  78                 $dbkey = $row->job_title;
  79                 $title = Title::makeTitleSafe( $namespace, $dbkey );
  80                 $job = Job::factory( $row->job_cmd, $title, Job::extractBlob( $row->job_params ),
  81                         $row->job_id );
  82
  83                 $dbw->delete( 'job', $job->insertFields(), __METHOD__ );
  84                 $dbw->commit();
  85
  86                 wfProfileOut( __METHOD__ );
  87                 return $job;
  88         }
  89
  90         /**
  91          * Pop a job off the front of the queue
  92          *
  93          * @param $offset Integer: Number of jobs to skip
  94          * @return Job or false if there's no jobs
  95          */
  96         static function pop( $offset = 0 ) {
  97                 wfProfileIn( __METHOD__ );
  98
  99                 $dbr = wfGetDB( DB_SLAVE );
 100
 101                 /* Get a job from the slave, start with an offset,
 102                         scan full set afterwards, avoid hitting purged rows
 103
 104                         NB: If random fetch previously was used, offset
 105                                 will always be ahead of few entries
 106                 */
 107
 108                 $row = $dbr->selectRow( 'job', '*', "job_id >= ${offset}", __METHOD__,
 109                         array( 'ORDER BY' => 'job_id', 'LIMIT' => 1 ) );
 110
 111                 // Refetching without offset is needed as some of job IDs could have had delayed commits
 112                 // and have lower IDs than jobs already executed, blame concurrency :)
 113                 //
 114                 if ( $row === false ) {
 115                         if ( $offset != 0 ) {
 116                                 $row = $dbr->selectRow( 'job', '*', '', __METHOD__,
 117                                         array( 'ORDER BY' => 'job_id', 'LIMIT' => 1 ) );
 118                         }
 119
 120                         if ( $row === false ) {
 121                                 wfProfileOut( __METHOD__ );
 122                                 return false;
 123                         }
 124                 }
 125
 126                 // Try to delete it from the master
 127                 $dbw = wfGetDB( DB_MASTER );
 128                 $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 129                 $affected = $dbw->affectedRows();
 130                 $dbw->commit();
 131
 132                 if ( !$affected ) {
 133                         // Failed, someone else beat us to it
 134                         // Try getting a random row
 135                         $row = $dbw->selectRow( 'job', array( 'MIN(job_id) as minjob',
 136                                 'MAX(job_id) as maxjob' ), '1=1', __METHOD__ );
 137                         if ( $row === false || is_null( $row->minjob ) || is_null( $row->maxjob ) ) {
 138                                 // No jobs to get
 139                                 wfProfileOut( __METHOD__ );
 140                                 return false;
 141                         }
 142                         // Get the random row
 143                         $row = $dbw->selectRow( 'job', '*',
 144                                 'job_id >= ' . mt_rand( $row->minjob, $row->maxjob ), __METHOD__ );
 145                         if ( $row === false ) {
 146                                 // Random job gone before we got the chance to select it
 147                                 // Give up
 148                                 wfProfileOut( __METHOD__ );
 149                                 return false;
 150                         }
 151                         // Delete the random row
 152                         $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 153                         $affected = $dbw->affectedRows();
 154                         $dbw->commit();
 155
 156                         if ( !$affected ) {
 157                                 // Random job gone before we exclusively deleted it
 158                                 // Give up
 159                                 wfProfileOut( __METHOD__ );
 160                                 return false;
 161                         }
 162                 }
 163
 164                 // If execution got to here, there's a row in $row that has been deleted from the database
 165                 // by this thread. Hence the concurrent pop was successful.
 166                 $namespace = $row->job_namespace;
 167                 $dbkey = $row->job_title;
 168                 $title = Title::makeTitleSafe( $namespace, $dbkey );
 169                 $job = Job::factory( $row->job_cmd, $title, Job::extractBlob( $row->job_params ), $row->job_id );
 170
 171                 // Remove any duplicates it may have later in the queue
 172                 // Deadlock prone section
 173                 $dbw->begin();
 174                 $dbw->delete( 'job', $job->insertFields(), __METHOD__ );
 175                 $dbw->commit();
 176
 177                 wfProfileOut( __METHOD__ );
 178                 return $job;
 179         }
 180
 181         /**
 182          * Create the appropriate object to handle a specific job
 183          *
 184          * @param $command String: Job command
 185          * @param $title Title: Associated title
 186          * @param $params Array: Job parameters
 187          * @param $id Int: Job identifier
 188          * @return Job
 189          */
 190         static function factory( $command, $title, $params = false, $id = 0 ) {
 191                 global $wgJobClasses;
 192                 if( isset( $wgJobClasses[$command] ) ) {
 193                         $class = $wgJobClasses[$command];
 194                         return new $class( $title, $params, $id );
 195                 }
 196                 throw new MWException( "Invalid job command `{$command}`" );
 197         }
 198
 199         static function makeBlob( $params ) {
 200                 if ( $params !== false ) {
 201                         return serialize( $params );
 202                 } else {
 203                         return '';
 204                 }
 205         }
 206
 207         static function extractBlob( $blob ) {
 208                 if ( (string)$blob !== '' ) {
 209                         return unserialize( $blob );
 210                 } else {
 211                         return false;
 212                 }
 213         }
 214
 215         /**
 216          * Batch-insert a group of jobs into the queue.
 217          * This will be wrapped in a transaction with a forced commit.
 218          *
 219          * This may add duplicate at insert time, but they will be
 220          * removed later on, when the first one is popped.
 221          *
 222          * @param $jobs array of Job objects
 223          */
 224         static function batchInsert( $jobs ) {
 225                 if( !count( $jobs ) ) {
 226                         return;
 227                 }
 228                 $dbw = wfGetDB( DB_MASTER );
 229                 $rows = array();
 230                 foreach( $jobs as $job ) {
 231                         $rows[] = $job->insertFields();
 232                         if ( count( $rows ) >= 50 ) {
 233                                 # Do a small transaction to avoid slave lag
 234                                 $dbw->begin();
 235                                 $dbw->insert( 'job', $rows, __METHOD__, 'IGNORE' );
 236                                 $dbw->commit();
 237                                 $rows = array();
 238                         }
 239                 }
 240                 if ( $rows ) {
 241                         $dbw->begin();
 242                         $dbw->insert( 'job', $rows, __METHOD__, 'IGNORE' );
 243                         $dbw->commit();
 244                 }
 245         }
 246
 247         /*-------------------------------------------------------------------------
 248          * Non-static functions
 249          *------------------------------------------------------------------------*/
 250
 251         /**
 252          * @param $command
 253          * @param $title
 254          * @param $params array
 255          * @param int $id
 256          */
 257         function __construct( $command, $title, $params = false, $id = 0 ) {
 258                 $this->command = $command;
 259                 $this->title = $title;
 260                 $this->params = $params;
 261                 $this->id = $id;
 262
 263                 // A bit of premature generalisation
 264                 // Oh well, the whole class is premature generalisation really
 265                 $this->removeDuplicates = true;
 266         }
 267
 268         /**
 269          * Insert a single job into the queue.
 270          * @return bool true on success
 271          */
 272         function insert() {
 273                 $fields = $this->insertFields();
 274
 275                 $dbw = wfGetDB( DB_MASTER );
 276
 277                 if ( $this->removeDuplicates ) {
 278                         $res = $dbw->select( 'job', array( '1' ), $fields, __METHOD__ );
 279                         if ( $dbw->numRows( $res ) ) {
 280                                 return;
 281                         }
 282                 }
 283                 return $dbw->insert( 'job', $fields, __METHOD__ );
 284         }
 285
 286         protected function insertFields() {
 287                 $dbw = wfGetDB( DB_MASTER );
 288                 return array(
 289                         'job_id' => $dbw->nextSequenceValue( 'job_job_id_seq' ),
 290                         'job_cmd' => $this->command,
 291                         'job_namespace' => $this->title->getNamespace(),
 292                         'job_title' => $this->title->getDBkey(),
 293                         'job_params' => Job::makeBlob( $this->params )
 294                 );
 295         }
 296
 297         function toString() {
 298                 $paramString = '';
 299                 if ( $this->params ) {
 300                         foreach ( $this->params as $key => $value ) {
 301                                 if ( $paramString != '' ) {
 302                                         $paramString .= ' ';
 303                                 }
 304                                 $paramString .= "$key=$value";
 305                         }
 306                 }
 307
 308                 if ( is_object( $this->title ) ) {
 309                         $s = "{$this->command} " . $this->title->getPrefixedDBkey();
 310                         if ( $paramString !== '' ) {
 311                                 $s .= ' ' . $paramString;
 312                         }
 313                         return $s;
 314                 } else {
 315                         return "{$this->command} $paramString";
 316                 }
 317         }
 318
 319         protected function setLastError( $error ) {
 320                 $this->error = $error;
 321         }
 322
 323         function getLastError() {
 324                 return $this->error;
 325         }
 326 }