Understanding Java Virtual Threads: Creation, Advantages, and Performance Considerations

Java virtual threads, introduced in Java 19, are lightweight threads (also called fibers or coroutines) that improve scalability and efficiency for applications handling many concurrent connections or requests.

They are implemented using Continuation Passing Style (CPS), a programming paradigm that passes control flow between code sections instead of relying on a central execution thread.

Differences Between Virtual Threads and Traditional Threads

Virtual threads are created via the new VirtualThreadFactory API, have much lower memory overhead, and integrate seamlessly with existing Java code, allowing developers to adopt them without rewriting applications.

To create a virtual thread, use VirtualThreadFactory which offers factory methods for various thread characteristics, such as Runnable or Callable tasks, or long‑running threads.

Example of creating a virtual thread:

VirtualThreadFactory factory = VirtualThreadFactory.builder().user(false).daemon(true).build();
VirtualThread thread = factory.newThread(() -> {
    System.out.println("Hello, world!");
});
thread.start();

In this example a daemon virtual thread factory is created, then a new virtual thread prints "Hello, world" to the console.

Virtual threads offer many advantages over traditional threads but also have drawbacks, such as limited suitability for fine‑grained scheduling control and potential incompatibility with third‑party libraries that assume traditional threads.

How to Create Virtual Threads

Use the VirtualThreadFactory class in the java.lang package. The basic steps are:

Call VirtualThreadFactory.builder() to create a factory instance.

Configure desired options (e.g., thread name prefix, daemon flag, user or system thread group).

Use the factory’s newThread() method with a Runnable or Callable to create a virtual thread.

Invoke the thread’s start() method to begin execution.

Another example:

VirtualThreadFactory factory = VirtualThreadFactory.builder()
        .user(false)
        .daemon(true)
        .namePrefix("MyVirtualThread")
        .build();
VirtualThread virtualThread = factory.newThread(() -> {
    // Do something useful
});
virtualThread.start();

Note that virtual threads consume far less memory than regular threads, enabling the creation of many more threads without exhausting system resources, though developers should still monitor total thread counts to avoid contention.

Advantages and Disadvantages of Virtual Threads

Key advantages:

Lower memory overhead because virtual threads share a single stack.

Improved scalability, allowing many more threads to be created.

Better resource utilization, reducing CPU, thread‑handle, and kernel‑thread consumption.

Simpler programming model using familiar control structures.

Seamless integration with existing code and concurrency utilities.

Key disadvantages:

Potential compatibility issues with libraries that assume traditional threads.

Synchronization challenges due to shared underlying OS threads.

Debugging and profiling can be more difficult.

Limited control over scheduling, as the JVM handles it.

Possible performance trade‑offs, such as slower context switches compared to native threads.

Performance Impact of Virtual Threads

The performance effect depends on the use case. Factors include task size (small, short‑lived tasks benefit most), contention levels, synchronization design, I/O‑bound workloads (where virtual threads excel), and overall resource utilization.

In many scenarios with many small or I/O‑bound tasks, virtual threads can provide significant performance gains, while long‑running, heavily synchronized tasks may see less benefit.

Conclusion

Java virtual threads are a promising feature that offers a lightweight, efficient way to manage concurrency, enabling higher scalability and simpler asynchronous code without sacrificing performance.

They are especially useful for applications that need to handle a large number of concurrent connections or I/O‑intensive workloads.

As developers become more familiar with virtual threads and adopt them in real‑world projects, their popularity is expected to grow.