Exploring Virtual Threads Java 21

Introduction

With the release of Java 21, the language has introduced a new feature called Virtual Threads. This new addition promises to change up how we handle multithreading and concurrency, increasing efficiency and simplifying the development of highly scalable applications.

In this article, we’ll look into the concept of Virtual Threads, their advantages, and how to use them in your next project.

What Are Virtual Threads?

To understand the innovation behind Virtual Threads, it's important to differentiate between "classic" Threads and Virtual Threads. In traditional Java, each Thread consumes significant system resources, and managing thousands of Threads can lead to scalability issues.

Virtual Threads, on the other hand, are a lightweight implementation of threads in Java. They allow us to handle thousands, even millions of threads without compromising performance. Essentially, Virtual Threads are managed by the JVM itself, but with a lightness that makes them more comparable to coroutines in languages like Kotlin or Go.

Why Are Virtual Threads Important?

In modern applications, like microservices, handling high concurrency is essential. Traditionally, the solution to this was to implement a Thread Pool, which helped limit the number of simultaneous threads but still left management challenges and complexity. With Virtual Threads, this complexity is drastically reduced:

• Scalability: Now, each client request can be handled by a Virtual Thread without the performance impact of traditional Threads.
• Simpler code: With less need for manual control and adjustments in thread pools, the code becomes more straightforward and easier to understand.
• Optimized performance: The JVM allocates Virtual Threads efficiently, allowing for a high degree of parallelism without requiring manual management.

These benefits help reduce system complexity and improve performance without requiring major changes to the code from developers.

Implementing Virtual Threads: Practical Example

Below, we have a practical example of how to create a Virtual Thread with the new Java 21. Let's compare it with the creation of traditional Threads and see how the new code is simpler and easier to manage.

// Traditional Thread
Thread traditionalThread = new Thread(() -> {
	System.out.println("Running traditional thread.");
});
traditionalThread.start();


// Virtual Thread
Thread virtualThread = Thread.ofVirtual().start(() -> {
	System.out.println("Running virtual thread.");
});        

Here’s an example of how you can use CompletableFuture with virtual threads:

import java.util.concurrent.CompletableFuture;

public class VirtualThreadCompletableFutureExample {
    public static void main(String[] args) {
        // Create a CompletableFuture that will be executed in a virtual thread
        CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
            // Simulate an I/O operation
            System.out.println("Executing in a virtual thread: " + Thread.currentThread());
            try {
                Thread.sleep(1000); // Simulates a delay
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
            System.out.println("Completed task in virtual thread.");
        }, Thread.ofVirtual().factory());

        // Wait for the CompletableFuture to complete
        future.join();

        System.out.println("Main thread continues...");
    }
}        

Details of the Example

• The above code uses CompletableFuture.runAsync() to execute an asynchronous task. The task is executed in a virtual thread using Thread.ofVirtual().factory(), which creates a factory for generating virtual threads.
• Inside the task, we simulate an I/O operation with Thread.sleep(1000). This represents an operation that could involve a network call or any other waiting operation.
• future.join() is called to block the main thread until the asynchronous task is completed, ensuring that the output of the task is displayed before continuing.

Virtual Threads are just as easy to create as traditional Threads, but they are managed by the JVM in a much more efficient way. They do not stay idle while waiting for resources, which means that the CPU can use them optimally.

Challenges and Considerations

As with any new feature, Virtual Threads come with some considerations:

• Interoperability: Not all libraries or frameworks have yet been adapted to fully support Virtual Threads.
• Debugging and Profiling: The massive use of Virtual Threads can complicate debugging and monitoring in certain scenarios, so it's important to understand the available tools.
• Gradual Learning: As with any programming feature, it’s advisable to adopt it gradually, testing its impact in your environment.

Over time, it is expected that the community will adopt this technology and improve support for Virtual Threads across various libraries.

Conclusion

Java 21 marks an important step for developers who need high concurrency in their applications, and Virtual Threads are a direct response to these demands.

This feature opens up new possibilities for building more scalable, lightweight, and efficient systems.

Although it’s a new addition, it’s worth starting to explore and experiment with Virtual Threads, as the potential for innovation and productivity gains is significant.