presto-main/src/main/java/io/prestosql/operator/exchange/LocalExchange.java/LocalExchange/createSinkFactory
class LocalExchange:    public synchronized LocalExchangeSinkFactory createSinkFactory()
    {
        checkState(!noMoreSinkFactories, "No more sink factories already set");
        LocalExchangeSinkFactory newFactory = new LocalExchangeSinkFactory(this);
        openSinkFactories.add(newFactory);
        return newFactory;
    }