presto-main/src/main/java/io/prestosql/operator/PartitionedLookupSourceFactory.java/PartitionedLookupSourceFactory/getSpilledLookupSourceHandle
class PartitionedLookupSourceFactory:    private SpilledLookupSourceHandle getSpilledLookupSourceHandle(int partitionNumber)
    {
        lock.readLock().lock();
        try {
            return requireNonNull(spilledPartitions.get(partitionNumber), "spilledPartitions.get(partitionNumber) is null");
        }
        finally {
            lock.readLock().unlock();
        }
    }