presto-main/src/main/java/io/prestosql/operator/aggregation/AbstractGroupCollectionAggregationState.java/AbstractGroupCollectionAggregationState/forEach
class AbstractGroupCollectionAggregationState:    public void forEach(T consumer)
    {
        short currentBlockId = headBlockIndex.get(getGroupId());
        int currentPosition = headPosition.get(getGroupId());
        while (currentBlockId != NULL) {
            accept(consumer, values.get(currentBlockId), currentPosition);

            long absoluteCurrentAddress = toAbsolutePosition(currentBlockId, currentPosition);
            currentBlockId = nextBlockIndex.get(absoluteCurrentAddress);
            currentPosition = nextPosition.get(absoluteCurrentAddress);
        }
    }