includes/job/JobQueue.php

   1 <?php
   2 /**
   3  * Job queue base code
   4  *
   5  * @file
   6  * @defgroup JobQueue JobQueue
   7  */
   8
   9 if ( !defined( 'MEDIAWIKI' ) ) {
  10         die( "This file is part of MediaWiki, it is not a valid entry point\n" );
  11 }
  12
  13 /**
  14  * Class to both describe a background job and handle jobs.
  15  *
  16  * @ingroup JobQueue
  17  */
  18 abstract class Job {
  19
  20         /**
  21          * @var Title
  22          */
  23         var $title;
  24
  25         var $command,
  26                 $params,
  27                 $id,
  28                 $removeDuplicates,
  29                 $error;
  30
  31         /*-------------------------------------------------------------------------
  32          * Abstract functions
  33          *------------------------------------------------------------------------*/
  34
  35         /**
  36          * Run the job
  37          * @return boolean success
  38          */
  39         abstract function run();
  40
  41         /*-------------------------------------------------------------------------
  42          * Static functions
  43          *------------------------------------------------------------------------*/
  44
  45         /**
  46          * Pop a job of a certain type.  This tries less hard than pop() to
  47          * actually find a job; it may be adversely affected by concurrent job
  48          * runners.
  49          */
  50         static function pop_type( $type ) {
  51                 wfProfilein( __METHOD__ );
  52
  53                 $dbw = wfGetDB( DB_MASTER );
  54
  55                 $row = $dbw->selectRow(
  56                         'job',
  57                         '*',
  58                         array( 'job_cmd' => $type ),
  59                         __METHOD__,
  60                         array( 'LIMIT' => 1 )
  61                 );
  62
  63                 if ( $row === false ) {
  64                         wfProfileOut( __METHOD__ );
  65                         return false;
  66                 }
  67
  68                 /* Ensure we "own" this row */
  69                 $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
  70                 $affected = $dbw->affectedRows();
  71
  72                 if ( $affected == 0 ) {
  73                         wfProfileOut( __METHOD__ );
  74                         return false;
  75                 }
  76
  77                 wfIncrStats( 'job-pop' );
  78                 $namespace = $row->job_namespace;
  79                 $dbkey = $row->job_title;
  80                 $title = Title::makeTitleSafe( $namespace, $dbkey );
  81                 $job = Job::factory( $row->job_cmd, $title, Job::extractBlob( $row->job_params ),
  82                         $row->job_id );
  83
  84                 $dbw->delete( 'job', $job->insertFields(), __METHOD__ );
  85                 $dbw->commit();
  86
  87                 wfProfileOut( __METHOD__ );
  88                 return $job;
  89         }
  90
  91         /**
  92          * Pop a job off the front of the queue
  93          *
  94          * @param $offset Integer: Number of jobs to skip
  95          * @return Job or false if there's no jobs
  96          */
  97         static function pop( $offset = 0 ) {
  98                 wfProfileIn( __METHOD__ );
  99
 100                 $dbr = wfGetDB( DB_SLAVE );
 101
 102                 /* Get a job from the slave, start with an offset,
 103                         scan full set afterwards, avoid hitting purged rows
 104
 105                         NB: If random fetch previously was used, offset
 106                                 will always be ahead of few entries
 107                 */
 108
 109                 $row = $dbr->selectRow( 'job', '*', "job_id >= ${offset}", __METHOD__,
 110                         array( 'ORDER BY' => 'job_id', 'LIMIT' => 1 ) );
 111
 112                 // Refetching without offset is needed as some of job IDs could have had delayed commits
 113                 // and have lower IDs than jobs already executed, blame concurrency :)
 114                 //
 115                 if ( $row === false ) {
 116                         if ( $offset != 0 ) {
 117                                 $row = $dbr->selectRow( 'job', '*', '', __METHOD__,
 118                                         array( 'ORDER BY' => 'job_id', 'LIMIT' => 1 ) );
 119                         }
 120
 121                         if ( $row === false ) {
 122                                 wfProfileOut( __METHOD__ );
 123                                 return false;
 124                         }
 125                 }
 126
 127                 // Try to delete it from the master
 128                 $dbw = wfGetDB( DB_MASTER );
 129                 $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 130                 $affected = $dbw->affectedRows();
 131                 $dbw->commit();
 132
 133                 if ( !$affected ) {
 134                         // Failed, someone else beat us to it
 135                         // Try getting a random row
 136                         $row = $dbw->selectRow( 'job', array( 'MIN(job_id) as minjob',
 137                                 'MAX(job_id) as maxjob' ), '1=1', __METHOD__ );
 138                         if ( $row === false || is_null( $row->minjob ) || is_null( $row->maxjob ) ) {
 139                                 // No jobs to get
 140                                 wfProfileOut( __METHOD__ );
 141                                 return false;
 142                         }
 143                         // Get the random row
 144                         $row = $dbw->selectRow( 'job', '*',
 145                                 'job_id >= ' . mt_rand( $row->minjob, $row->maxjob ), __METHOD__ );
 146                         if ( $row === false ) {
 147                                 // Random job gone before we got the chance to select it
 148                                 // Give up
 149                                 wfProfileOut( __METHOD__ );
 150                                 return false;
 151                         }
 152                         // Delete the random row
 153                         $dbw->delete( 'job', array( 'job_id' => $row->job_id ), __METHOD__ );
 154                         $affected = $dbw->affectedRows();
 155                         $dbw->commit();
 156
 157                         if ( !$affected ) {
 158                                 // Random job gone before we exclusively deleted it
 159                                 // Give up
 160                                 wfProfileOut( __METHOD__ );
 161                                 return false;
 162                         }
 163                 }
 164
 165                 // If execution got to here, there's a row in $row that has been deleted from the database
 166                 // by this thread. Hence the concurrent pop was successful.
 167                 wfIncrStats( 'job-pop' );
 168                 $namespace = $row->job_namespace;
 169                 $dbkey = $row->job_title;
 170                 $title = Title::makeTitleSafe( $namespace, $dbkey );
 171                 $job = Job::factory( $row->job_cmd, $title, Job::extractBlob( $row->job_params ), $row->job_id );
 172
 173                 // Remove any duplicates it may have later in the queue
 174                 // Deadlock prone section
 175                 $dbw->begin();
 176                 $dbw->delete( 'job', $job->insertFields(), __METHOD__ );
 177                 $dbw->commit();
 178
 179                 wfProfileOut( __METHOD__ );
 180                 return $job;
 181         }
 182
 183         /**
 184          * Create the appropriate object to handle a specific job
 185          *
 186          * @param $command String: Job command
 187          * @param $title Title: Associated title
 188          * @param $params Array: Job parameters
 189          * @param $id Int: Job identifier
 190          * @return Job
 191          */
 192         static function factory( $command, $title, $params = false, $id = 0 ) {
 193                 global $wgJobClasses;
 194                 if( isset( $wgJobClasses[$command] ) ) {
 195                         $class = $wgJobClasses[$command];
 196                         return new $class( $title, $params, $id );
 197                 }
 198                 throw new MWException( "Invalid job command `{$command}`" );
 199         }
 200
 201         static function makeBlob( $params ) {
 202                 if ( $params !== false ) {
 203                         return serialize( $params );
 204                 } else {
 205                         return '';
 206                 }
 207         }
 208
 209         static function extractBlob( $blob ) {
 210                 if ( (string)$blob !== '' ) {
 211                         return unserialize( $blob );
 212                 } else {
 213                         return false;
 214                 }
 215         }
 216
 217         /**
 218          * Batch-insert a group of jobs into the queue.
 219          * This will be wrapped in a transaction with a forced commit.
 220          *
 221          * This may add duplicate at insert time, but they will be
 222          * removed later on, when the first one is popped.
 223          *
 224          * @param $jobs array of Job objects
 225          */
 226         static function batchInsert( $jobs ) {
 227                 if( !count( $jobs ) ) {
 228                         return;
 229                 }
 230                 $dbw = wfGetDB( DB_MASTER );
 231                 $rows = array();
 232                 foreach( $jobs as $job ) {
 233                         $rows[] = $job->insertFields();
 234                         if ( count( $rows ) >= 50 ) {
 235                                 # Do a small transaction to avoid slave lag
 236                                 $dbw->begin();
 237                                 $dbw->insert( 'job', $rows, __METHOD__, 'IGNORE' );
 238                                 $dbw->commit();
 239                                 $rows = array();
 240                         }
 241                 }
 242                 if ( $rows ) {
 243                         wfIncrStats( 'job-insert', count( $rows ) );
 244                         $dbw->begin();
 245                         $dbw->insert( 'job', $rows, __METHOD__, 'IGNORE' );
 246                         $dbw->commit();
 247                 }
 248         }
 249
 250         /*-------------------------------------------------------------------------
 251          * Non-static functions
 252          *------------------------------------------------------------------------*/
 253
 254         /**
 255          * @param $command
 256          * @param $title
 257          * @param $params array
 258          * @param int $id
 259          */
 260         function __construct( $command, $title, $params = false, $id = 0 ) {
 261                 $this->command = $command;
 262                 $this->title = $title;
 263                 $this->params = $params;
 264                 $this->id = $id;
 265
 266                 // A bit of premature generalisation
 267                 // Oh well, the whole class is premature generalisation really
 268                 $this->removeDuplicates = true;
 269         }
 270
 271         /**
 272          * Insert a single job into the queue.
 273          * @return bool true on success
 274          */
 275         function insert() {
 276                 $fields = $this->insertFields();
 277
 278                 $dbw = wfGetDB( DB_MASTER );
 279
 280                 if ( $this->removeDuplicates ) {
 281                         $res = $dbw->select( 'job', array( '1' ), $fields, __METHOD__ );
 282                         if ( $dbw->numRows( $res ) ) {
 283                                 return;
 284                         }
 285                 }
 286                 wfIncrStats( 'job-insert' );
 287                 return $dbw->insert( 'job', $fields, __METHOD__ );
 288         }
 289
 290         protected function insertFields() {
 291                 $dbw = wfGetDB( DB_MASTER );
 292                 return array(
 293                         'job_id' => $dbw->nextSequenceValue( 'job_job_id_seq' ),
 294                         'job_cmd' => $this->command,
 295                         'job_namespace' => $this->title->getNamespace(),
 296                         'job_title' => $this->title->getDBkey(),
 297                         'job_params' => Job::makeBlob( $this->params )
 298                 );
 299         }
 300
 301         function toString() {
 302                 $paramString = '';
 303                 if ( $this->params ) {
 304                         foreach ( $this->params as $key => $value ) {
 305                                 if ( $paramString != '' ) {
 306                                         $paramString .= ' ';
 307                                 }
 308                                 $paramString .= "$key=$value";
 309                         }
 310                 }
 311
 312                 if ( is_object( $this->title ) ) {
 313                         $s = "{$this->command} " . $this->title->getPrefixedDBkey();
 314                         if ( $paramString !== '' ) {
 315                                 $s .= ' ' . $paramString;
 316                         }
 317                         return $s;
 318                 } else {
 319                         return "{$this->command} $paramString";
 320                 }
 321         }
 322
 323         protected function setLastError( $error ) {
 324                 $this->error = $error;
 325         }
 326
 327         function getLastError() {
 328                 return $this->error;
 329         }
 330 }