Java Virtual Threads

Summary

In this video, the presenter introduces virtual threads, a new feature added in Java 19. Virtual threads are lightweight and managed by platform threads, which are executed by operating system threads. The video explains the difference between virtual threads and traditional platform threads, highlighting how virtual threads can enhance performance by allowing better utilization of platform threads. Virtual threads also use less memory, enabling applications to handle millions of them. The presenter demonstrates how to create, start, and manage virtual threads, and shares code examples. Additionally, virtual threads are still in preview, and developers need to enable preview features to use them.

Takeaways

• 😀 Virtual threads are a new feature in Java 19, providing lightweight and efficient concurrency management.
• 😀 Platform threads are traditional OS-managed threads, while virtual threads are managed by platform threads and execute on OS threads.
• 😀 Virtual threads are initially queued within the Java platform until a platform thread is available to execute them.
• 😀 When a virtual thread blocks (e.g., during network calls), it can be unmounted from the platform thread, allowing the platform thread to execute another virtual thread.
• 😀 Virtual threads allow for better resource utilization, particularly in scenarios where threads perform blocking I/O operations.
• 😀 Virtual threads consume much less memory than platform threads, making it possible to run millions of them within the same application.
• 😀 To create a virtual thread, use the `Thread.ofVirtual().start()` method, which is similar to how platform threads are started.
• 😀 Virtual threads can be joined using the `join()` method, just like platform threads, ensuring synchronization.
• 😀 With virtual threads, it is possible to create and manage large numbers of threads (e.g., 100,000 or more) without significant performance issues.
• 😀 Virtual threads are still a preview feature in Java 19, and you must enable them via the `--enable-preview` flag during both compilation and execution.

Q & A

What are virtual threads in Java 19?

Virtual threads are a new feature introduced in Java 19 that provides a lightweight, more efficient way of managing concurrency. Unlike platform threads, which are directly tied to operating system threads, virtual threads are executed by platform threads, allowing better resource utilization and scalability.

How are platform threads different from virtual threads in Java?

Platform threads are standard threads executed directly by the operating system, whereas virtual threads are managed by the JVM and executed by platform threads. Virtual threads are lightweight and designed for handling large numbers of concurrent tasks with lower memory overhead.

What happens when a virtual thread is blocked in Java?

When a virtual thread is blocked (e.g., waiting for I/O operations), it is unmounted from the platform thread, which can then execute another virtual thread. Once the virtual thread is unblocked, it is placed back in the ready queue for execution by a platform thread.

What are the advantages of using virtual threads over platform threads?

The main advantages of virtual threads are their lightweight nature, which allows running millions of them without consuming a lot of memory, and their ability to efficiently handle blocking operations by unmounting from platform threads and avoiding wasting resources.

How can virtual threads be created in Java?

Virtual threads in Java are created using the static method `Thread.ofVirtual().start()` to immediately start a virtual thread, or `Thread.ofVirtual().unstarted()` to create one without starting it. Both methods accept a `Runnable` object as a parameter, just like with platform threads.

How do you join a virtual thread in Java?

To join a virtual thread, you call the `join()` method on the thread object, just as you would with a platform thread. This will block the calling thread until the virtual thread has finished executing.

How does the JVM manage the execution of virtual threads?

The JVM manages the execution of virtual threads by keeping a small number of platform threads ready to execute them. When a virtual thread is ready, the JVM mounts it to a platform thread. If the virtual thread blocks, it is unmounted, allowing the platform thread to handle other tasks.

What is the maximum number of virtual threads you can create in a Java application?

In theory, you can create millions of virtual threads in a Java application. Unlike platform threads, which are heavy and resource-intensive, virtual threads are lightweight and do not consume significant memory, making it feasible to create and manage large numbers of them.

Why is there no guarantee that virtual threads will execute in the order they are created?

Virtual threads are scheduled by the JVM, and the execution order can vary depending on when platform threads become available to execute them. The threads are not guaranteed to execute in the order they were created because the scheduling is influenced by factors like thread availability and resource allocation.

How do you enable virtual threads in Java 19 if they are still in preview?

To use virtual threads in Java 19, you need to enable preview features. This can be done by using the `--enable-preview` flag both when compiling and running the code, either in your IDE (like IntelliJ) or from the command line.