WANObjectCacheReaper.php

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<?php
use Psr\Log\LoggerAwareInterface;
use Psr\Log\LoggerInterface;
use Psr\Log\NullLogger;
use Wikimedia\ScopedCallback;
 
class WANObjectCacheReaper implements LoggerAwareInterface {
    protected $cache;
    protected $store;
    protected $logChunkCallback;
    protected $keyListCallback;
    protected $logger;
 
    protected $channel;
    protected $initialStartWindow;
 
    public function __construct(
        WANObjectCache $cache,
        BagOStuff $store,
        callable $logCallback,
        callable $keyCallback,
        array $params
    ) {
        $this->cache = $cache;
        $this->store = $store;
 
        $this->logChunkCallback = $logCallback;
        $this->keyListCallback = $keyCallback;
        if ( isset( $params['channel'] ) ) {
            $this->channel = $params['channel'];
        } else {
            throw new UnexpectedValueException( "No channel specified." );
        }
 
        $this->initialStartWindow = $params['initialStartWindow'] ?? 3600;
        $this->logger = $params['logger'] ?? new NullLogger();
    }
 
    public function setLogger( LoggerInterface $logger ) {
        $this->logger = $logger;
    }
 
    final public function invoke( $n = 100 ) {
        $posKey = $this->store->makeGlobalKey( 'WANCache', 'reaper', $this->channel );
        $scopeLock = $this->store->getScopedLock( "$posKey:busy", 0 );
        if ( !$scopeLock ) {
            return 0;
        }
 
        $now = time();
        $status = $this->store->get( $posKey );
        if ( !$status ) {
            $status = [ 'pos' => $now - $this->initialStartWindow, 'id' => null ];
        }
 
        // Get events for entities who's keys tombstones/hold-off should have expired by now
        $events = call_user_func_array(
            $this->logChunkCallback,
            [ $status['pos'], $status['id'], $now - WANObjectCache::HOLDOFF_TTL - 1, $n ]
        );
 
        $event = null;
        $keyEvents = [];
        foreach ( $events as $event ) {
            $keys = call_user_func_array(
                $this->keyListCallback,
                [ $this->cache, $event['item'] ]
            );
            foreach ( $keys as $key ) {
                unset( $keyEvents[$key] ); // use only the latest per key
                $keyEvents[$key] = [
                    'pos' => $event['pos'],
                    'id' => $event['id']
                ];
            }
        }
 
        $purgeCount = 0;
        $lastOkEvent = null;
        foreach ( $keyEvents as $key => $keyEvent ) {
            if ( !$this->cache->reap( $key, $keyEvent['pos'] ) ) {
                break;
            }
            ++$purgeCount;
            $lastOkEvent = $event;
        }
 
        if ( $lastOkEvent ) {
            $ok = $this->store->merge(
                $posKey,
                function ( $bag, $key, $curValue ) use ( $lastOkEvent ) {
                    if ( !$curValue ) {
                        // Use new position
                    } else {
                        $curCoord = [ $curValue['pos'], $curValue['id'] ];
                        $newCoord = [ $lastOkEvent['pos'], $lastOkEvent['id'] ];
                        if ( $newCoord < $curCoord ) {
                            // Keep prior position instead of rolling it back
                            return $curValue;
                        }
                    }
 
                    return [
                        'pos' => $lastOkEvent['pos'],
                        'id' => $lastOkEvent['id'],
                        'ctime' => $curValue ? $curValue['ctime'] : date( 'c' )
                    ];
                },
                BagOStuff::TTL_INDEFINITE
            );
 
            $pos = $lastOkEvent['pos'];
            $id = $lastOkEvent['id'];
            if ( $ok ) {
                $this->logger->info( "Updated cache reap position ($pos, $id)." );
            } else {
                $this->logger->error( "Could not update cache reap position ($pos, $id)." );
            }
        }
 
        ScopedCallback::consume( $scopeLock );
 
        return $purgeCount;
    }
 
    public function getState() {
        $posKey = $this->store->makeGlobalKey( 'WANCache', 'reaper', $this->channel );
 
        return $this->store->get( $posKey );
    }
}