presto-main/src/main/java/io/prestosql/operator/PartitionedConsumption.java/Partition/release
class Partition:        public synchronized void release()
        {
            checkState(loaded.isDone());
            pendingReleases--;
            checkState(pendingReleases >= 0);
            if (pendingReleases == 0) {
                released.set(null);
            }
        }