includes/JobQueue.php

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