How to get materialized value from CompletionStage without blocking

Akka Libraries Akka Streams & Alpakka
1

I have code:

final ActorSystem system = ActorSystem.create(“test-stream”);
final Materializer mat = ActorMaterializer.create(system);
final Source<Integer, NotUsed> source = Source.range(1, 100);
final Sink<Integer, CompletionStage> sinkTotal = Sink.fold(0, (aggr, next) → { return aggr + next;});
final RunnableGraph<CompletionStage> graph = source.toMat(sinkTotal, Keep.right());
final CompletionStage sum = graph.run(mat);
int total = sum.toCompletableFuture().get());

To get the final sum value, I need to do:

sum.toCompletableFuture().get();

But get() method is blocking.
How can I access the final value without blocking the main thread?

2

Well if that’s all your code…? I don’t see where mat comes from? Do you just have a mistake in that it should be graph.run(graph);?

3

I didn’t show ActorSystem, Materializer related code. Now its there.

4

It depends. If you have some javascript background you will totally fine with the callback way. But in other cases you need to wait it. The main question is; you need the result in the main thread? (Most of the cases you don’t need it there.)