presto-main/src/main/java/io/prestosql/operator/index/IndexLookupSourceFactory.java/IndexLookupSourceFactory/createLookupSourceProvider
class IndexLookupSourceFactory:    @Override
    public ListenableFuture<LookupSourceProvider> createLookupSourceProvider()
    {
        checkState(taskContext != null, "taskContext not set");

        IndexLoader indexLoader = indexLoaderSupplier.get();
        indexLoader.setContext(taskContext);
        return Futures.immediateFuture(new StaticLookupSourceProvider(new IndexLookupSource(indexLoader)));
    }