Java 19 introduced Virtual Threads, also known as Project Loom, which provides a lightweight alternative to traditional threads. This feature allows Java to handle millions of concurrent tasks efficiently without the overhead of platform (OS) threads.
1. What Are Virtual Threads?
✅ Virtual Threads (Thread.ofVirtual()) are lightweight user-mode threads.
✅ Java can create millions of Virtual Threads without blocking OS resources.
✅ Each Virtual Thread is managed by the JVM, not the OS.
✅ Ideal for high-concurrency applications (e.g., web servers, APIs, and real-time processing).
2. Traditional Threads vs. Virtual Threads
🔴 Before Java 19 (Traditional Platform Threads)
- Each Java thread is mapped to an OS thread, limiting scalability.
- Creating too many threads (
new Thread()) is expensive. - Blocking operations (
sleep(),wait(),IO) waste OS resources.
🟢 Java 19+ (Virtual Threads Are Lightweight!)
- Thousands (or millions) of Virtual Threads can run on a few OS threads.
- More efficient for blocking tasks (e.g., database calls, network requests).
📌 Example: Creating a Virtual Thread
public class Main {
public static void main(String[] args) throws Exception {
Thread vThread = Thread.ofVirtual().start(() -> System.out.println("Hello from a Virtual Thread!"));
vThread.join(); // Wait for the Virtual Thread to finish
}
}✅ Output:
Hello from a Virtual Thread!✔ Runs like a normal thread but is much lighter!
3. Running Multiple Virtual Threads (Millions of Them!)
📌 Example: Launching 1 Million Virtual Threads
import java.util.stream.IntStream;
public class Main {
public static void main(String[] args) {
IntStream.range(0, 1_000_000).forEach(i ->
Thread.ofVirtual().start(() -> System.out.println("Thread: " + i))
);
}
}✅ Output:
Thread: 0
Thread: 1
Thread: 2
...
Thread: 999999✔ No OS slowdown! Virtual Threads allow massive concurrency.
4. Virtual Threads and Executors (Executors.newVirtualThreadPerTaskExecutor())
📌 Example: Using a Virtual Thread Executor
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class Main {
public static void main(String[] args) {
try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 1000; i++) {
executor.submit(() -> System.out.println(Thread.currentThread()));
}
}
}
}✅ Output (Threads are dynamically created and destroyed):
VirtualThread[#5]/runnable
VirtualThread[#6]/runnable
VirtualThread[#7]/runnable
...✔ No need to manage thread pools manually!
5. When Should You Use Virtual Threads?
🚀 Use Virtual Threads when:
✔ You need massive concurrency (thousands or millions of tasks).
✔ You perform blocking operations (e.g., database queries, HTTP requests).
✔ You want a lightweight alternative to traditional threads.
🚨 Do NOT use Virtual Threads when:
❌ You perform heavy CPU computations (Use traditional ForkJoinPool instead).
❌ Your tasks need fine-grained thread control.
6. Comparison: Before Java 19 vs. Java 19+ (Virtual Threads)
| Feature | Platform Threads (new Thread()) | Virtual Threads (Thread.ofVirtual()) |
|---|---|---|
| Thread Management | Handled by OS | Handled by JVM |
| Thread Cost | High (OS thread per Java thread) | Low (millions of Virtual Threads possible) |
| Best For | CPU-bound tasks | IO-bound tasks (HTTP, DB) |
| Blocking | Wasteful | Lightweight and efficient |
Lesson Reflection
- How do Virtual Threads improve scalability in Java applications?
- Why are Virtual Threads better for IO-bound tasks rather than CPU-bound tasks?
- Can you think of a real-world scenario where Virtual Threads would be useful?
Answers to Reflection Questions on Virtual Threads (Java 19+)
1️⃣ How do Virtual Threads improve scalability in Java applications?
✅ Traditional Java threads are mapped to OS threads, which are heavy and limited.
✅ Virtual Threads (Thread.ofVirtual()) are managed by the JVM, allowing millions of them to exist efficiently.
✅ Virtual Threads are lightweight, making them ideal for high-concurrency applications like web servers, APIs, and databases.
📌 Example: Handling 1 Million Requests Efficiently
🔴 Before Java 19 (Platform Threads, Expensive!)
ExecutorService executor = Executors.newFixedThreadPool(100);
for (int i = 0; i < 1_000_000; i++) {
executor.submit(() -> {
Thread.sleep(1000); // Simulate I/O operation
System.out.println("Request handled");
});
}
executor.shutdown();❌ Problem: Limited by the number of OS threads (100 in the pool).
🟢 Java 19+ (Virtual Threads, Scales to Millions!)
try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 1_000_000; i++) {
executor.submit(() -> {
Thread.sleep(1000); // ✅ Non-blocking with Virtual Threads
System.out.println("Request handled");
});
}
}✅ Handles 1 million requests without performance issues!
✔ Virtual Threads improve scalability by handling many more concurrent tasks efficiently.
2️⃣ Why are Virtual Threads better for IO-bound tasks rather than CPU-bound tasks?
🚀 Virtual Threads are designed to handle tasks that spend time waiting (I/O-bound).
✅ I/O-Bound Tasks (Good Use Case for Virtual Threads)
- Reading/writing to a database.
- Making HTTP API calls.
- Handling user requests in a web server.
✅ Example: Making HTTP Calls Concurrently
try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 1000; i++) {
executor.submit(() -> {
// Simulate an HTTP request
Thread.sleep(1000);
System.out.println("HTTP request completed");
});
}
}✔ Since Virtual Threads don’t block OS threads, they work well with slow I/O operations.
❌ CPU-Bound Tasks (Not Good for Virtual Threads)
- Processing large datasets.
- Performing complex calculations (AI, Machine Learning).
- Rendering graphics.
🔴 Example: Heavy CPU Computation (Better with ForkJoinPool)
ExecutorService executor = Executors.newFixedThreadPool(10); // Better for CPU tasks
for (int i = 0; i < 100; i++) {
executor.submit(() -> {
long result = 0;
for (long j = 0; j < 1_000_000_000; j++) { result += j; } // Heavy computation
System.out.println("Computation done: " + result);
});
}
executor.shutdown();✔ For CPU-heavy tasks, traditional threads work better because they map to real CPU cores.
3️⃣ Can you think of a real-world scenario where Virtual Threads would be useful?
🚀 Example 1: Handling High-Traffic Web Servers (Millions of Concurrent Requests)
✔ A web server that handles millions of users (e.g., Twitter, Facebook).
✔ Virtual Threads allow each request to have its own thread without OS limits.
🚀 Example 2: High-Concurrency Databases
✔ A banking system processing millions of transactions.
✔ Virtual Threads allow efficient database query execution.
🚀 Example 3: Chat Applications (WhatsApp, Discord, Slack)
✔ Each user connection runs in a Virtual Thread, reducing memory usage.
📌 Example: Building a Scalable Web Server
import java.util.concurrent.*;
public class WebServer {
public static void main(String[] args) {
try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
for (int i = 0; i < 1_000_000; i++) {
executor.submit(() -> {
Thread.sleep(500); // Simulate user request processing
System.out.println("Handled user request");
});
}
}
}
}✅ Handles 1 million requests efficiently!
✔ Virtual Threads shine in scenarios where high concurrency is needed, but CPU work is minimal.
🔍 Key Takeaways
✔ Virtual Threads scale better than traditional threads by reducing OS overhead.
✔ They are best for I/O-bound tasks (database calls, API requests, etc.).
✔ They are NOT ideal for CPU-intensive tasks (use ForkJoinPool instead).
✔ Real-world use cases include web servers, chat apps, and high-concurrency systems.
The next Java 21+ feature: Scoped Values (ScopedValue for thread-local data sharing) 😊🚀
