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