As a Java developer, you may have already heard about virtual threads, a powerful feature introduced in Project Loom. Virtual threads provide a lightweight alternative to traditional threads, making writing scalable and efficient concurrent code easier. In this blog post, we will discuss migration tips for Java developers who want to make the most of virtual threads.

Understand the differences between virtual and native threads

Before diving into the migration, it’s crucial to understand the fundamental differences between virtual threads (also known as “fibers”) and native threads. The operating system manages native threads, while virtual threads are managed by the Java Virtual Machine (JVM). This means that virtual threads have much lower overhead, allowing you to create millions of them without running into resource limitations.

Start using virtual threads

You can start experimenting with virtual threads by creating a virtual thread executor using the java.util.concurrent.ExecutorService. Here’s a simple example:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class VirtualThreadExample {

    public static void main(String[] args) {
        ExecutorService executor = Executors.newVirtualThreadExecutor();

        executor.submit(() -> {
            System.out.println("Hello from a virtual thread!");
        });

        executor.shutdown();
    }
}

In this example, we create a virtual thread executor and submit a task to be executed by a virtual thread.

Migrate from Thread to ExecutorService for concurrency

When migrating from native threads to virtual threads, it’s essential to replace direct usage of the Thread class with the ExecutorService. Consider the following native thread example:

public class NativeThreadExample {

    public static void main(String[] args) {
        Thread thread = new Thread(() -> {
            System.out.println("Hello from a native thread!");
        });

        thread.start();

        try {
            thread.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

The equivalent example using virtual threads would look like this:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class VirtualThreadExample {

    public static void main(String[] args) {
        ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();

        executor.submit(() -> {
            System.out.println("Hello from a virtual thread!");
        });

        executor.shutdown();
    }
}

Handle blocking operations

When working with virtual threads, it’s essential to be aware of blocking operations. You can use java.util.concurrent.CompletableFuture to manage blocking tasks and integrate them seamlessly with virtual threads. Here’s an example:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class FutureExample {

    public static void main(String[] args) {
        ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();

        Future<String> future = executor.submit(() -> {
            return blockingOperation();
        });

        try {
            String result = future.get();
            System.out.println("Result: " + result);
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }

        executor.shutdown();
    }

    private static String blockingOperation() {
        // Simulate a blocking operation
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "Blocking operation completed";
    }
}

In this example, we submit a blocking operation to the virtual thread executor, which returns a Future object. We then use Future.get() to block and wait for the result of the blocking operation. Thanks to virtual threads, this blocking style can be used without incurring the same performance penalties typically associated with native threads.

Conclusion

Migrating from native threads to virtual threads in Java can significantly improve the performance and scalability of your concurrent applications. By reducing the overhead associated with native threads, virtual threads enable you to create millions of lightweight threads without running into resource limitations. This allows you to write more efficient, parallelized code that can handle a larger number of concurrent tasks.

When transitioning to virtual threads, it’s crucial to replace direct usage of the Thread class with the ExecutorService, which provides a more flexible and powerful way to manage concurrency. Additionally, handling blocking operations using CompletableFuture ensures that your virtual threads remain efficient and responsive.

By embracing virtual threads and adopting these migration tips, Java developers can unlock new levels of performance in their concurrent applications. This powerful feature from Project Loom can help you write cleaner, more maintainable code while achieving superior scalability and responsiveness. As the Java ecosystem continues to evolve, virtual threads are set to play a key role in the future of high-performance, concurrent programming.