I’m very new to Vert.x and I decided to try it hoping that it offers Future api similar to Scala Future or even Cats/ZIO IO, but it seems that I cannot run multiple futures in parallel from my main function.

I figured out that by default they are run on a single threaded event loop, and it seems there is no way of specifying a custom event loop (Vertx instance) for the Future to run. In their libraries (such as postgresql client) they use their internal api:

ContextInternal current = vertx.getOrCreateContext();
if (pipelined) {
    return current.failedFuture("Cannot acquire a connection on a pipelined pool");
}
Promise<SqlConnectionPool.PooledConnection> promise = current.promise();

But from the application code I cannot use ContextInternal, only Context. Here is my code, I took it from the older question but changed it a little bit:

package com.example;

import io.vertx.core.*;
import io.vertx.core.impl.ContextInternal;

public class FuturesTest {

    static Vertx vertx = Vertx.vertx();
    public static long fib(int n) {
        long a = 0, b = 1;
        for (int i = 1; i < n; i++) {
            var x = a;
            a = b;
            b = x + b;
        }
        return b;
    }
    public static Future<Void> runTask(String m) {
        return Future.future(p -> {
            System.out.println("running " + m);
            p.complete();
        }).map(p -> {
            System.out.println("30th fibonacci num is " + fib(30)); //Calling a method that calculates the nth fibonacci
            return null;
        }).<Void>map(p -> {
            System.out.println("completed running " + m);
            return null;
        }).onComplete(p -> System.out.println(m + " completed"));
    }

    public static void main(String[] args) throws Exception {

        var f1 = runTask("Future one");

        var f2 = runTask("Future two");

        var ff = Future.any(f1, f2).onComplete(ar ->{
            if(ar.succeeded()){
                System.out.println("All succeeded");
            } else {
                System.out.println("At least one failed");
            }
        });


        Thread.sleep(5000);
        System.out.println("EXIT");
    }
}

How can I run the future on the specified event loop from the application level?

I’m trying to achieve it purely with Futures, avoiding executeBlocking() or similar methods but I haven’t found a way to change the default event loop to use multiple threads. I don’t want to create multiple event loops like in this question but make the Futures run in the multiple threads.