CompletableFutures newWorkStealingPool test

G1Test.java

import org.junit.Test;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class G1Test {
    Logger logger = LoggerFactory.getLogger(G1Test.class);

    // ExecutorService e1 = Executors.newFixedThreadPool(2);
    ExecutorService e1 = Executors.newWorkStealingPool(2);

    @Test
    public void test() {
        // Gather CompletableFutures to wait for them at the end
        List<CompletableFuture> futures = new ArrayList<>();

        // First steps
        for (int i = 0; i < 5; i++) {
            int finalI = i;
            CompletableFuture<Void> fut = CompletableFuture.supplyAsync(() -> {
                logger.info("Start step a - " + finalI);
                //simulateLongProcessing();// just waits for 1 s
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                logger.info("End step a - " + finalI);
                return "step1 output - " + finalI;
            }, e1)
                    .orTimeout(5000, TimeUnit.MILLISECONDS)
                    .exceptionally(t -> "exp 1 output " + finalI)
                    .thenComposeAsync(s -> {
                        List<CompletableFuture> subFutures = new ArrayList<>();
                        // Second step : Launch several sub-tasks based on the result of the first step
                        for (int j = 0; j < 5; j++) {
                            final int finalJ = j;
                            CompletableFuture<String> f = CompletableFuture.supplyAsync(() -> {
                                logger.info("Start - step b : " + s + " | " + finalJ);
                                //simulateLongProcessing();
                                logger.info("End - step b : " + s + " | " + finalJ);
                                return "step2 output - " + s + " | " + finalJ;
                            }, e1);
                            subFutures.add(f);
                        }
                        return CompletableFuture.allOf(subFutures.toArray(new CompletableFuture[0]));
                    }, e1);
            futures.add(fut);
        }

        // Wait for the completion
        for (CompletableFuture future : futures) {
            future.join();
        }
    }
}