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' ), "job_id >= $offset", __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                 $dbw->delete( 'job', $job->insertFields(), __METHOD__ );
 167
 168                 wfProfileOut( __METHOD__ );
 169                 return $job;
 170         }
 171
 172         /**
 173          * Create the appropriate object to handle a specific job
 174          *
 175          * @param $command String: Job command
 176          * @param $title Title: Associated title
 177          * @param $params Array: Job parameters
 178          * @param $id Int: Job identifier
 179          * @return Job
 180          */
 181         static function factory( $command, $title, $params = false, $id = 0 ) {
 182                 global $wgJobClasses;
 183                 if( isset( $wgJobClasses[$command] ) ) {
 184                         $class = $wgJobClasses[$command];
 185                         return new $class( $title, $params, $id );
 186                 }
 187                 throw new MWException( "Invalid job command `{$command}`" );
 188         }
 189
 190         static function makeBlob( $params ) {
 191                 if ( $params !== false ) {
 192                         return serialize( $params );
 193                 } else {
 194                         return '';
 195                 }
 196         }
 197
 198         static function extractBlob( $blob ) {
 199                 if ( (string)$blob !== '' ) {
 200                         return unserialize( $blob );
 201                 } else {
 202                         return false;
 203                 }
 204         }
 205
 206         /**
 207          * Batch-insert a group of jobs into the queue.
 208          * This will be wrapped in a transaction with a forced commit.
 209          *
 210          * This may add duplicate at insert time, but they will be
 211          * removed later on, when the first one is popped.
 212          *
 213          * @param $jobs array of Job objects
 214          */
 215         static function batchInsert( $jobs ) {
 216                 if( count( $jobs ) ) {
 217                         $dbw = wfGetDB( DB_MASTER );
 218                         $dbw->begin();
 219                         foreach( $jobs as $job ) {
 220                                 $rows[] = $job->insertFields();
 221                         }
 222                         $dbw->insert( 'job', $rows, __METHOD__, 'IGNORE' );
 223                         $dbw->commit();
 224                 }
 225         }
 226
 227         /*-------------------------------------------------------------------------
 228          * Non-static functions
 229          *------------------------------------------------------------------------*/
 230
 231         function __construct( $command, $title, $params = false, $id = 0 ) {
 232                 $this->command = $command;
 233                 $this->title = $title;
 234                 $this->params = $params;
 235                 $this->id = $id;
 236
 237                 // A bit of premature generalisation
 238                 // Oh well, the whole class is premature generalisation really
 239                 $this->removeDuplicates = true;
 240         }
 241
 242         /**
 243          * Insert a single job into the queue.
 244          */
 245         function insert() {
 246                 $fields = $this->insertFields();
 247
 248                 $dbw = wfGetDB( DB_MASTER );
 249
 250                 if ( $this->removeDuplicates ) {
 251                         $res = $dbw->select( 'job', array( '1' ), $fields, __METHOD__ );
 252                         if ( $dbw->numRows( $res ) ) {
 253                                 return;
 254                         }
 255                 }
 256                 $fields['job_id'] = $dbw->nextSequenceValue( 'job_job_id_seq' );
 257                 $dbw->insert( 'job', $fields, __METHOD__ );
 258         }
 259
 260         protected function insertFields() {
 261                 return array(
 262                         'job_cmd' => $this->command,
 263                         'job_namespace' => $this->title->getNamespace(),
 264                         'job_title' => $this->title->getDBkey(),
 265                         'job_params' => Job::makeBlob( $this->params )
 266                 );
 267         }
 268
 269         function toString() {
 270                 $paramString = '';
 271                 if ( $this->params ) {
 272                         foreach ( $this->params as $key => $value ) {
 273                                 if ( $paramString != '' ) {
 274                                         $paramString .= ' ';
 275                                 }
 276                                 $paramString .= "$key=$value";
 277                         }
 278                 }
 279
 280                 if ( is_object( $this->title ) ) {
 281                         $s = "{$this->command} " . $this->title->getPrefixedDBkey();
 282                         if ( $paramString !== '' ) {
 283                                 $s .= ' ' . $paramString;
 284                         }
 285                         return $s;
 286                 } else {
 287                         return "{$this->command} $paramString";
 288                 }
 289         }
 290
 291         function getLastError() {
 292                 return $this->error;
 293         }
 294 }