How to run the Java Incubator Module from the Command Line and IntelliJ IDEA

JEP 425: Virtual Threads (Preview) has been proposed recently. It has been a long-awaited feature in Java. It opens the door to Structured Concurrency. This article isn’t about it, in case you are interested, you can read, the JEP draft: Structured Concurrency (Incubator)

Also, if you are interested in how the incubator module works, please read: JEP 11: Incubator Modules

I downloaded the early access build and wrote the following very simple program that demonstrates structure concurrency.

import jdk.incubator.concurrent.StructuredTaskScope;

import java.util.Random;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

public class Main {
    public static void main(String[] args) {
        int fooBaz = foo();
        System.out.println("fooBaz = " + fooBaz);
    }

    private static int foo() {
        try (var taskScope = new StructuredTaskScope.ShutdownOnFailure()) {
            Future f1 = taskScope.fork(Main::baz);
            Future f2 = taskScope.fork(Main::baz);

            taskScope.join();
            return f1.resultNow() + f2.resultNow();
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

    private static int baz() {
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        return new Random().nextInt();
    }
}

I tried to run the command line using the source code launcher but end up getting the following error-

$ java Main.java 

Main.java:1: error: package jdk.incubator.concurrent is not visible
import jdk.incubator.concurrent.StructuredTaskScope;
                    ^
  (package jdk.incubator.concurrent is declared in module jdk.incubator.concurrent, which is not in the module graph)
1 error
error: compilation failed

The reason is that the features are being developed under the incubator module which isn’t visible. If we want to use the module, we need to explicitly add a module while you run it. Let’s fix it.

$ java --add-modules jdk.incubator.concurrent Main.java

WARNING: Using incubator modules: jdk.incubator.concurrent
warning: using incubating module(s): jdk.incubator.concurrent
1 warning
fooBaz = 327780169

It worked.

Then I thought why not do it with my favourite IDE, IntelliJ IDEA.

Here are the steps: –

First, we need to go preference, and then Build, Execution, Deployment and then Select Java Compiler.