MultiWriteBagOStuff.php

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<?php
class MultiWriteBagOStuff extends BagOStuff {
    protected $caches;
    protected $asyncWrites = false;

    const ALL = INF;

    const UPGRADE_TTL = 3600; // TTL when a key is copied to a higher cache tier

    public function __construct( $params ) {
        parent::__construct( $params );

        if ( empty( $params['caches'] ) || !is_array( $params['caches'] ) ) {
            throw new InvalidArgumentException(
                __METHOD__ . ': "caches" parameter must be an array of caches'
            );
        }

        $this->caches = [];
        foreach ( $params['caches'] as $cacheInfo ) {
            if ( $cacheInfo instanceof BagOStuff ) {
                $this->caches[] = $cacheInfo;
            } else {
                if ( !isset( $cacheInfo['args'] ) ) {
                    // B/C for when $cacheInfo was for ObjectCache::newFromParams().
                    // Callers intenting this to be for ObjectFactory::getObjectFromSpec
                    // should have set "args" per the docs above. Doings so avoids extra
                    // (likely harmless) params (factory/class/calls) ending up in "args".
                    $cacheInfo['args'] = [ $cacheInfo ];
                }
                $this->caches[] = ObjectFactory::getObjectFromSpec( $cacheInfo );
            }
        }
        $this->mergeFlagMaps( $this->caches );

        $this->asyncWrites = (
            isset( $params['replication'] ) &&
            $params['replication'] === 'async' &&
            is_callable( $this->asyncHandler )
        );
    }

    public function setDebug( $debug ) {
        foreach ( $this->caches as $cache ) {
            $cache->setDebug( $debug );
        }
    }

    protected function doGet( $key, $flags = 0 ) {
        if ( ( $flags & self::READ_LATEST ) == self::READ_LATEST ) {
            // If the latest write was a delete(), we do NOT want to fallback
            // to the other tiers and possibly see the old value. Also, this
            // is used by mergeViaLock(), which only needs to hit the primary.
            return $this->caches[0]->get( $key, $flags );
        }

        $misses = 0; // number backends checked
        $value = false;
        foreach ( $this->caches as $cache ) {
            $value = $cache->get( $key, $flags );
            if ( $value !== false ) {
                break;
            }
            ++$misses;
        }

        if ( $value !== false
            && $misses > 0
            && ( $flags & self::READ_VERIFIED ) == self::READ_VERIFIED
        ) {
            $this->doWrite( $misses, $this->asyncWrites, 'set', $key, $value, self::UPGRADE_TTL );
        }

        return $value;
    }

    public function set( $key, $value, $exptime = 0, $flags = 0 ) {
        $asyncWrites = ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC )
            ? false
            : $this->asyncWrites;

        return $this->doWrite( self::ALL, $asyncWrites, 'set', $key, $value, $exptime );
    }

    public function delete( $key ) {
        return $this->doWrite( self::ALL, $this->asyncWrites, 'delete', $key );
    }

    public function add( $key, $value, $exptime = 0 ) {
        return $this->doWrite( self::ALL, $this->asyncWrites, 'add', $key, $value, $exptime );
    }

    public function incr( $key, $value = 1 ) {
        return $this->doWrite( self::ALL, $this->asyncWrites, 'incr', $key, $value );
    }

    public function decr( $key, $value = 1 ) {
        return $this->doWrite( self::ALL, $this->asyncWrites, 'decr', $key, $value );
    }

    public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
        // Only need to lock the first cache; also avoids deadlocks
        return $this->caches[0]->lock( $key, $timeout, $expiry, $rclass );
    }

    public function unlock( $key ) {
        // Only the first cache is locked
        return $this->caches[0]->unlock( $key );
    }

    public function getLastError() {
        return $this->caches[0]->getLastError();
    }

    public function clearLastError() {
        $this->caches[0]->clearLastError();
    }

    protected function doWrite( $count, $asyncWrites, $method /*, ... */ ) {
        $ret = true;
        $args = array_slice( func_get_args(), 3 );

        foreach ( $this->caches as $i => $cache ) {
            if ( $i >= $count ) {
                break; // ignore the lower tiers
            }

            if ( $i == 0 || !$asyncWrites ) {
                // First store or in sync mode: write now and get result
                if ( !call_user_func_array( [ $cache, $method ], $args ) ) {
                    $ret = false;
                }
            } else {
                // Secondary write in async mode: do not block this HTTP request
                $logger = $this->logger;
                call_user_func(
                    $this->asyncHandler,
                    function () use ( $cache, $method, $args, $logger ) {
                        if ( !call_user_func_array( [ $cache, $method ], $args ) ) {
                            $logger->warning( "Async $method op failed" );
                        }
                    }
                );
            }
        }

        return $ret;
    }

    public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
        $ret = false;
        foreach ( $this->caches as $cache ) {
            if ( $cache->deleteObjectsExpiringBefore( $date, $progressCallback ) ) {
                $ret = true;
            }
        }

        return $ret;
    }
}