presto-main/src/main/java/io/prestosql/operator/exchange/LocalExchange.java/LocalExchange/sinkFinished
class LocalExchange:    private void sinkFinished(LocalExchangeSink sink)
    {
        checkNotHoldsLock(this);

        synchronized (this) {
            sinks.remove(sink);
        }
        checkAllSinksComplete();
    }