Java 21 introduces a game-changer Virtual Threads! Let's break down what this feature is, how it differs from the traditional model, and its pros and cons.

What are Virtual Threads?

In previous versions of Java, creating a thread meant tying it directly to an operating system (OS) thread, which is a limited resource. Spinning up a large number of OS threads often led to performance bottlenecks and increased memory usage. With Java 21, Virtual Threads (a.k.a. Project Loom) aim to solve this by offering lightweight, manageable threads that are decoupled from OS threads.

🤔 Simply put: Think of virtual threads as micro-sized threads that allow you to handle thousands of concurrent tasks more efficiently without hogging system resources.

The Old Thread Model vs. Virtual Threads

Java's old thread model, based on "platform threads," required each Java thread to have a 1:1 mapping to an OS thread. While reliable, it also meant:

Memory Limitations: Platform threads took up significant memory.
Scaling Issues: Managing a high number of threads could overload system resources.
Blocking I/O Problems: OS threads waiting on I/O blocked other operations, slowing performance.

Enter Virtual Threads! 🦸‍♂️
Virtual Threads allow you to create millions of threads without resource strain. They're not bound to OS threads, so when a virtual thread is blocked (e.g., waiting for I/O), the underlying carrier thread can pick up another virtual thread to keep things running smoothly.

Traditional Threads vs. Virtual Threads

TRADITIONAL THREADS                        VIRTUAL THREADS
---------------------------------          ---------------------------------
| Java Thread -> OS Thread -> Task |       | Virtual Thread -> Carrier OS Thread |
| Java Thread -> OS Thread -> Task |  ->   | Virtual Thread -> Carrier OS Thread |
| Java Thread -> OS Thread -> Task |       | Virtual Thread -> Carrier OS Thread |
---------------------------------          ---------------------------------

In Virtual Threads, multiple virtual threads can be assigned to one OS thread, optimizing resource allocation.

Pros and Cons of Virtual Threads

Pros

Higher Scalability: Handle millions of threads, making it perfect for server-side applications.
Less Memory Usage: Virtual threads are lightweight, meaning each one doesn’t require a full OS thread.
Efficient Blocking I/O: When virtual threads encounter blocking I/O, carrier threads can pick up other tasks, keeping the system active.
Better Resource Management: Threads are no longer restricted to a limited pool of OS threads, so fewer resources are wasted.

Cons

Learning Curve: Virtual threads introduce new concurrency concepts which may require rethinking existing thread management practices.
New Debugging Challenges: Debugging thousands (or even millions) of virtual threads can be more complex.
Not Ideal for All Applications: Single-threaded applications or those with minimal concurrency won’t benefit much from virtual threads.

Code Example: Traditional vs. Virtual Threads

Let’s look at a simple example of traditional threads and compare it to virtual threads.

Traditional Threads

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

Virtual Threads (Java 21)

Virtual Threads are managed independently by the Java Virtual Machine (JVM) and aren’t limited to OS threads.

public class VirtualThreadExample {
    public static void main(String[] args) {
        Thread.startVirtualThread(() -> System.out.println("Hello from a virtual thread!"));
    }
}

sample example of running 100000 tasks using the platform and virtual threads.

package virtualthreads.samples;

import java.time.Duration;
import java.time.Instant;
import java.util.concurrent.Executors;
import java.util.stream.IntStream;

public class PlatformVsVirtualThreadsSamples {

    public static void main(String[] args) {
        PlatformVsVirtualThreadsSamples platformVsVirtualThreadsSamples = new PlatformVsVirtualThreadsSamples();
        platformVsVirtualThreadsSamples.platformThreadsExecution();
        platformVsVirtualThreadsSamples.virtualThreadsExecution();
    }
    public void platformThreadsExecution(){
        var begin = Instant.now();
        try(var executor = Executors.newCachedThreadPool()){
            IntStream.range(0,100_000).forEach(i-> executor.submit(() -> {
                Thread.sleep(Duration.ofSeconds(1));
                return i;
            }));
        }
        var end = Instant.now();
        System.out.println("platformThreadsExecution : Duration of execution: "+Duration.between(begin,end));
    }
    public void virtualThreadsExecution(){
        var begin = Instant.now();
        try(var executor = Executors.newVirtualThreadPerTaskExecutor()){
            IntStream.range(0,100_000).forEach(i-> executor.submit(() -> {
                Thread.sleep(Duration.ofSeconds(1));
                return i;
            }));
        }
        var end = Instant.now();
        System.out.println("virtualThreadsExecution : Duration of execution: "+Duration.between(begin,end));
    }
}

When Should You Use Virtual Threads?

• Server Applications: Handling multiple simultaneous requests, such as web servers or database connections.
• I/O-Bound Applications: These are especially applications with heavy I/O operations like file processing, network requests, or web scraping.
• Cloud-native Microservices: Systems requiring high scalability will benefit from virtual threads.

Conclusion: The Future of Concurrency is Here 🌟

With the introduction of virtual threads in Java 21, managing concurrent tasks is more efficient, scalable, and lightweight than ever. Whether you’re handling hundreds or millions of tasks, virtual threads provide a pathway to a simpler and more resource-friendly way of programming in Java.