includes/JobQueue.php

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