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