#Java 21 — Article 2: Mastering About Virtual Threads.

1)What Are Virtual Threads?

Virtual Threads are a new type of thread in Java, introduced in Java 21 (via Project Loom), that are:

• Lightweight: You can create thousands or even millions of them with very little memory overhead.
• Managed by the JVM: The Java Virtual Machine schedules and manages them for you, so they don’t use one operating system thread per Java thread (unlike “platform threads”).

2)Why Use Virtual Threads?

• 1)Lightweight: You can create thousands or even millions of them with very little memory overhead.
• 2)Easier Concurrency: You can write concurrent code (like servers or processing lots of tasks at once) using ordinary Java code, without needing to learn complex async patterns.
• 3)Highly Scalable: Because they’re so lightweight, you can run many more concurrent tasks than you could with traditional (platform) threads.
• 4)Same API : You still use familiar Java APIs like Runnable, Thread, ExecutorService, etc.

3)Creating a Virtual Thread

Java

Thread.startVirtualThread(() -> 
{     
System.out.println("Hello from a virtual thread!");
});

4)Using ExecutorService to create Virtual Threads

Java

try (var executor = Executors.newVirtualThreadPerTaskExecutor()) 
{     
executor.submit(() -> 
{         
// Code runs in a virtual thread         
System.out.println("Virtual thread says hi!");     
}); 
}

• With Executors.newVirtualThreadPerTaskExecutor(), each task submitted runs in its own virtual thread.
• You can run tens of thousands (or more) of these in parallel!

Example Usage

Java

try (var executor = Executors.newVirtualThreadPerTaskExecutor()) 
{     for (int i = 0; i < 100_000; i++) 
{         executor.submit(() -> {             
// Simulate work             Thread.sleep(1000);         
});     
} 
}

You can start 100,000 (or more!) tasks, and Java manages them all for you with ease.

5) How Are Virtual Threads Different from Platform Threads?

6)When Should I Use Virtual Threads?

• Server applications (e.g., handling thousands of client requests)
• Concurrent data processing
• Any program that needs to run lots of tasks at once
• Virtual Threads let you write simple, readable, blocking code yet scale to handle huge numbers of tasks.
• You don’t need to re-architect for async/non-blocking if you want scalability!
• They work seamlessly with traditional Java concurrency APIs.

7) Other documentation for Virtual Threads

https://openjdk.org/jeps/444

Summary sentence: Virtual threads are easy-to-use, super-light threads built into Java, letting you run huge numbers of tasks at once, simply and scalably, without changing how you write your code.

What are Virtual Threads?

• Virtual threads are a new kind of lightweight thread in Java.
• You can create thousands or millions of them easily — they use much less memory and resources than traditional threads.

Why Did Java Add Virtual Threads?

• In the past, each thread in Java used a “real” operating system thread, which are limited and expensive. This limited how many tasks could run at once.
• If you wanted high performance for lots of tasks, you had to write complex, tricky asynchronous code — harder to understand, debug, and maintain.

How Do Virtual Threads Help?

• With virtual threads, you can go back to writing simple, one-thread-per-task code (often called “thread-per-request”), even for huge numbers of tasks.
• Virtual threads are fully managed by the Java runtime.
• The JVM schedules lots of virtual threads onto fewer operating system threads automatically and efficiently.

Example Usage

Java

try (var executor = Executors.newVirtualThreadPerTaskExecutor()) 
{     
for (int i = 0; i < 100_000; i++) 
{         
executor.submit(() -> 
{             
// Simulate work             
Thread.sleep(1000);         
});     
} 
}

You can start 100,000 (or more!) tasks, and Java manages them all for you with ease.

Key Benefits

• Simple, old-style code: You can use familiar blocking calls and simple loops — no need for tricky async code.
• Highly scalable: You can easily handle tens/hundreds of thousands of concurrent tasks.
• Easy debugging: Standard Java tools (profilers, debuggers, stack traces) work with virtual threads.
• No pooling needed: Virtual threads are cheap; just create as many as you need and throw them away when done.

What Doesn’t Change

• Virtual threads don’t run faster than platform threads — they’re just lighter and more scalable.
• If you are doing heavy CPU work, you still need to think about how many “real” threads are available.
• Not all old tricks (like pooling threads or using thread-local storage for shared resources) work the same.

In Short

• Java virtual threads make it super easy to write highly concurrent programs without learning new programming styles.
• Most older Java libraries just work, and your server or app can handle much more work with less overhead!
• Create a new virtual thread wherever you’d naturally use a thread — for example, to handle each user request on a busy server.

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