$memcKey = 'jobqueue:dbs:v3';
$pendingDbInfo = $wgMemc->get( $memcKey );
- // If the cache entry wasn't present, or in 1% of cases otherwise,
- // regenerate the cache. Use any available stale cache if another
- // process is currently regenerating the pending DB information.
- if ( !$pendingDbInfo || mt_rand( 0, 100 ) == 0 ) {
- $lock = $wgMemc->add( 'jobqueue:dbs:v3:lock', 1, 1800 ); // lock
- if ( $lock ) {
+ // If the cache entry wasn't present, is stale, or in .1% of cases otherwise,
+ // regenerate the cache. Use any available stale cache if another process is
+ // currently regenerating the pending DB information.
+ if ( !is_array( $pendingDbInfo )
+ || ( time() - $pendingDbInfo['timestamp'] ) > 300 // 5 minutes
+ || mt_rand( 0, 999 ) == 0
+ ) {
+ if ( $wgMemc->add( "$memcKey:rebuild", 1, 1800 ) ) { // lock
$pendingDbInfo = array(
'pendingDBs' => $this->getPendingDbs(),
'timestamp' => time()
);
- $wgMemc->set( $memcKey, $pendingDbInfo );
- $wgMemc->delete( 'jobqueue:dbs:v3:lock' ); // unlock
+ for ( $attempts=1; $attempts <= 25; ++$attempts ) {
+ if ( $wgMemc->add( "$memcKey:lock", 1, 60 ) ) { // lock
+ $wgMemc->set( $memcKey, $pendingDbInfo );
+ $wgMemc->delete( "$memcKey:lock" ); // unlock
+ break;
+ }
+ }
+ $wgMemc->delete( "$memcKey:rebuild" ); // unlock
}
}
- if ( !$pendingDbInfo || !$pendingDbInfo['pendingDBs'] ) {
+ if ( !is_array( $pendingDbInfo ) || !$pendingDbInfo['pendingDBs'] ) {
return; // no DBs with jobs or cache is both empty and locked
}
- $pendingDBs = $pendingDbInfo['pendingDBs'];
+ $pendingDBs = $pendingDbInfo['pendingDBs']; // convenience
do {
$again = false;
// There are no jobs of this type available in the current database
$pendingDBs[$type] = array_diff( $pendingDBs[$type], array( $db ) );
}
- // Update the cache to remove the outdated information
+ // Update the cache to remove the outdated information.
+ // Make sure that this does not race (especially with full rebuilds).
$pendingDbInfo['pendingDBs'] = $pendingDBs;
- // @TODO: fix race condition with these updates
- $wgMemc->set( $memcKey, $pendingDbInfo );
+ if ( $wgMemc->add( "$memcKey:lock", 1, 60 ) ) { // lock
+ $curInfo = $wgMemc->get( $memcKey );
+ if ( $curInfo && $curInfo['timestamp'] === $pendingDbInfo['timestamp'] ) {
+ $wgMemc->set( $memcKey, $pendingDbInfo );
+ }
+ $wgMemc->delete( "$memcKey:lock" ); // unlock
+ }
$again = true;
}
} while ( $again );