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Advanced 22 min readModule: Module 10: Concurrency, Threads & Virtual Threads (Project Loom)

Java 21 Virtual Threads & Concurrency

Scale to 1,000,000 concurrent tasks effortlessly using lightweight Java 21 Virtual Threads (Project Loom).

What You Will Learn in This Lesson

  • OS Platform Threads (1MB memory) vs Virtual Threads (KB memory)
  • Spawning virtual threads with Executors.newVirtualThreadPerTaskExecutor()
  • CompletableFuture for asynchronous pipeline composition

Introduction & Core Concept

Virtual Threads are lightweight threads that dramatically reduce the effort of writing, maintaining, and observing high-throughput concurrent applications.
WHY DOES THIS MATTER IN THE REAL WORLD?

Traditional OS threads hit memory limits at ~5,000 threads. Virtual threads allow a single JVM to easily manage 1,000,000 concurrent HTTP connections!

Spawning 10,000 Virtual Threads

java
java
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import java.util.concurrent.Executors;
 
public class VirtualThreadDemo {
    public static void main(String[] args) {
        try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
            for (int i = 1; i <= 5; i++) {
                final int id = i;
                executor.submit(() -> {
                    System.out.println("Virtual Thread Task #" + id + " running.");
                });
            }
        }
    }
}

Line-by-Line Technical Breakdown

1Virtual threads eliminate the need for complex reactive programming (like WebFlux/RxJava) for high-throughput I/O.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

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Industry Best Practices & Professional Standards

  • Never pool virtual threads; spawn a new virtual thread per task.

Lesson Summary & Core Takeaways

  • Virtual Threads bring effortless, high-throughput concurrency to modern Java.