How does Java handle multithreading and what are Virtual Threads (Project Loom)?

Explanation & Concept

Traditionally, every `java.lang.Thread` mapped 1:1 to an operating system kernel thread, consuming ~1MB of stack memory and making millions of concurrent threads impractical.

Java 21 introduced **Virtual Threads**: lightweight, JVM-managed user-mode threads that run on a small pool of carrier OS threads. When a virtual thread blocks on socket I/O, the JVM unmounts it and runs another task, allowing millions of concurrent tasks with standard blocking code.

Code Example

java

import java.util.concurrent.Executors;

public class VirtualThreadDemo {
    public static void main(String[] args) {
        // Create an executor that spawns a virtual thread per task
        try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
            for (int i = 0; i < 10_000; i++) {
                final int taskId = i;
                executor.submit(() -> {
                    Thread.sleep(100); // Does NOT block an OS thread!
                    return "Task " + taskId + " complete";
                });
            }
        } // Automatically waits for all 10,000 tasks to finish!
        System.out.println("All virtual threads finished!");
    }
}

How It Works & Key Takeaways

Spawning 10,000 platform threads would exhaust OS memory. Virtual threads consume only bytes of RAM and yield carrier threads during `Thread.sleep` or I/O.

Mock Test · 1 Questions · Optional

Ready for Generics?

Take a quick test to evaluate yourself, or move straight to the next module.

Intermediate2 questions

Skip

Multithreading & ConcurrencyBeginner

1Question 1 of 1

java

How does Java handle multithreading and what are Virtual Threads (Project Loom)?

Explanation & Concept

Traditionally, every `java.lang.Thread` mapped 1:1 to an operating system kernel thread, consuming ~1MB of stack memory and making millions of concurrent threads impractical.

Code Example

java

import java.util.concurrent.Executors;

public class VirtualThreadDemo {
    public static void main(String[] args) {
        // Create an executor that spawns a virtual thread per task
        try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
            for (int i = 0; i < 10_000; i++) {
                final int taskId = i;
                executor.submit(() -> {
                    Thread.sleep(100); // Does NOT block an OS thread!
                    return "Task " + taskId + " complete";
                });
            }
        } // Automatically waits for all 10,000 tasks to finish!
        System.out.println("All virtual threads finished!");
    }
}

How It Works & Key Takeaways

Spawning 10,000 platform threads would exhaust OS memory. Virtual threads consume only bytes of RAM and yield carrier threads during `Thread.sleep` or I/O.

Mock Test · 1 Questions · Optional

Ready for Generics?

Take a quick test to evaluate yourself, or move straight to the next module.

Intermediate2 questions

Skip