private static void initMetaStreamEvent(MetaStreamEvent metaStreamEvent, AbstractDefinition inputDefinition,
                                            String inputReferenceId) {
        metaStreamEvent.addInputDefinition(inputDefinition);
        metaStreamEvent.setInputReferenceId(inputReferenceId);
        metaStreamEvent.initializeOnAfterWindowData();
        inputDefinition.getAttributeList().forEach(metaStreamEvent::addData);
    }
Aggregation runtime managing aggregation operations for aggregation definition.
modules/siddhi-core/src/main/java/io/siddhi/core/aggregation/AggregationRuntime.java