Use Vert.x worker threads to run a for-loop.

ConcurrentLoop.java

import io.vertx.core.*;


public class ConcurrentLoop {

    private static String runTask(int idx) {
        System.out.println("run task " + idx + " on " + Thread.currentThread().getName());
        long sum = 0;
        for (long j = 0; j < Long.MAX_VALUE / 1000000000; j++) {
            sum += 1;
        }
        System.out.println("finish task " + idx);
        return String.valueOf(sum);
    }

    public static void main(String[] args) {

        long start1 = System.nanoTime();
        runTask(0);
        long end1 = System.nanoTime();
        System.out.println("all done, time " + (end1 - start1) / 1000000 + " ms");


        long start2 = System.nanoTime();
        Vertx vertx = Vertx.vertx();
        List futureList = new ArrayList();
        for (int i = 0; i < 5; i++) {
            Future taskFuture = Future.future();
            futureList.add(taskFuture);
            final int idx = i;
            vertx.<String>executeBlocking(fut -> {
                runTask(idx);
                fut.complete();
            }, false, res -> {

                taskFuture.complete("result " + idx + " = " + res.result());
            });
        }
        CompositeFuture.join(futureList).setHandler(res -> {
            long end2 = System.nanoTime();
            System.out.println("all done, time " + (end2 - start2) / 1000000 + " ms");
            List<String> lst = res.result().list();
            for (String s : lst) {
                System.out.println(s);
            }
        });
    }

}

/**
run task 0 on main
finish task 0
all done, time 5310 ms
run task 0 on vert.x-worker-thread-0
run task 1 on vert.x-worker-thread-1
run task 2 on vert.x-worker-thread-2
run task 3 on vert.x-worker-thread-3
run task 4 on vert.x-worker-thread-4
finish task 1
finish task 0
finish task 3
finish task 2
finish task 4
all done, time 13730 ms
result 0 = null
result 1 = null
result 2 = null
result 3 = null
result 4 = null
*/