Different pop method

diff --git a/includes/JobQueue.php b/includes/JobQueue.php
index 8874f49..17ef11d 100644 (file)
--- a/includes/JobQueue.php
+++ b/includes/JobQueue.php
@@ -38,44 +38,63 @@ class Job {
                $fname = 'Job::pop';
                wfProfileIn( $fname );
 
-               // First check to see if there are any jobs in the slave DB
                $dbr =& wfGetDB( DB_SLAVE );
-               $id = $dbr->selectField( 'job', 'job_id', '', $fname, array( 'LIMIT' => 1 ) );
-               if ( $id === false ) {
+
+               // Get a job from the slave
+               $row = $dbr->selectRow( 'job', '*', '', $fname, 
+                       array( 'ORDER BY' => 'job_id', 'LIMIT' => 1 )
+               );
+
+               if ( $row === false ) {
                        wfProfileOut( $fname );
                        return false;
                }
 
-               // Pop an item off the front of the queue
-               // Method due to Domas, may not work on all DBMSes
+               // Try to delete it from the master
                $dbw =& wfGetDB( DB_MASTER );
-               $jobTable = $dbw->tableName( 'job' );
-               $dbw->query( "DELETE FROM $jobTable WHERE " .
-                       '(job_cmd = @job_cmd := job_cmd) AND ' .
-                       '(job_namespace = @job_namespace := job_namespace) AND ' .
-                       '(job_title = @job_title := job_title) AND ' .
-                       '(job_params = @job_params := job_params) ' .
-                       'LIMIT 1', $fname );
+               $dbw->delete( 'job', array( 'job_id' => $row->job_id ), $fname );
                $affected = $dbw->affectedRows();
-               // Commit now before 100 other threads pile up behind us
                $dbw->immediateCommit();
-               if ( !$affected ) {
-                       wfProfileOut( $fname );
-                       return false;
-               }
 
-               $res = $dbw->query( "SELECT @job_cmd, @job_namespace, @job_title, @job_params", $fname );
-               $row = $dbw->fetchRow( $res );
-               if ( !$row ) {
-                       wfProfileOut( $fname );
-                       return false;
+               if ( !$affected ) {
+                       // Failed, someone else beat us to it
+                       // Try getting a random row
+                       $row = $dbw->selectRow( 'job', array( 'MIN(job_id) as minjob', 
+                               'MAX(job_id) as maxjob' ), $fname );
+                       if ( $row === false || is_null( $row->minjob ) || is_null( $row->maxjob ) ) {
+                               // No jobs to get
+                               wfProfileOut( $fname );
+                               return false;
+                       }
+                       // Get the random row
+                       $row = $dbw->selectRow( 'job', '*', 
+                               array( 'job_id' => mt_rand( $row->minjob, $row->maxjob ) ),     $fname );
+                       if ( $row === false ) {
+                               // Random job gone before we got the chance to select it
+                               // Give up
+                               wfProfileOut( $fname );
+                               return false;
+                       }
+                       // Delete the random row
+                       $dbw->delete( 'job', array( 'job_id' => $row->job_id ), $fname );
+                       $affected = $dbw->affectedRows();
+                       $dbw->immediateCommit();
+                       
+                       if ( !$affected ) {
+                               // Random job gone before we exclusively deleted it
+                               // Give up
+                               wfProfileOut( $fname );
+                               return false;
+                       }                               
                }
-
-               $command = $row['@job_cmd'];
-               $namespace = $row['@job_namespace'];
-               $dbkey = $row['@job_title'];
+               
+               // If execution got to here, there's a row in $row that has been deleted from the database
+               // by this thread. Hence the concurrent pop was successful.
+               $command = $row->job_cmd;
+               $namespace = $row->job_namespace;
+               $dbkey = $row->job_title;
                $title = Title::makeTitleSafe( $namespace, $dbkey );
-               $params = $row['@job_params'];
+               $params = $row->job_params;
                $job = new Job( $command, $title, $params );
                wfProfileOut( $fname );
                return $job;