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However, the CPU would be far from being utilized since it would spend most of its time waiting for responses from the external services, even if several threads are served per CPU core. Its goal is to dramatically reduce the effort of writing, maintaining, and observing high-throughput concurrent applications. It is too early to be considering using virtual threads in production but now is the time to include Project Loom and virtual threads in your planning so you are ready when virtual threads are generally available in the JRE. Virtual threads were named “fibers” for a time, but that name was abandoned in favor of “virtual threads” to avoid confusion with fibers in other languages. While I do think virtual threads are a great feature, I also feel paragraphs like the above will lead to a fair amount of scale hype-train’ism.

Of course, these are simple use cases; both thread pools and virtual thread implementations can be further optimized for better performance, but that’s not the point of this post. In this GitHub repository you can find a sample Spring application with the controller shown above. The README explains how to start the application and how to switch the controller from platform threads to virtual threads.

comments on “Virtual Threads in Java (Project Loom)”

And then it’s your responsibility to check back again later, to find out if there is any new data to be read. When you open up the JavaDoc of inputStream.readAllBytes() (or are lucky enough to remember your Java 101 class), it gets hammered into you that the call is blocking, i.e. won’t return until all the bytes are read – your current thread is blocked until then. Apiumhub brings together a community of software developers & architects to help you transform your idea into a powerful and scalable product. Our Tech Hub specialises in Software Architecture, Web Development & Mobile App Development.

By the way, you can find out if code is running in a virtual thread with Thread.currentThread().isVirtual(). Not only is this code hard to read and maintain, but it is also extremely difficult to debug. For example, it would make no sense to set a breakpoint here because the code only defines the asynchronous flow but does not execute it.

Virtual Threads – Example

Read on for an overview of Project Loom and how it proposes to modernize Java concurrency. For these situations, we would have to carefully write workarounds and failsafe, putting all the burden on the developer. But with file access, there is no async IO (well, except for io_uring in new kernels).

This will increase performance and scalability in most cases based on the benchmarks out there. Structured concurrency can help simplify the multi-threading or parallel processing use cases and make them less fragile and more maintainable. IIUC, the real benefit of a virtual thread is when you have a blocking I/O operation. With Loom, the underlying carrier thread will continue executing other tasks while your virtual thread blocks. Before Loom, this distinction was not made – there was only one type of threads – and the blocking I/O was not a feasible option for high throughput applications, like web servers. The last pitfall is a bit subtle but important for scalability since Virtual Threads can scale in number orders of magnitude more compared to platform threads, and it’s about thread inheritance.

What about the Thread.sleep example?

The downside is that Java threads are mapped directly to the threads in the operating system (OS). This places a hard limit on the scalability of concurrent Java applications. Not only does it imply a one-to-one relationship between application threads and OS threads, but there is no mechanism for organizing threads for optimal arrangement. http://protyazhno.ru/anpagelin90-1.html For instance, threads that are closely related may wind up sharing different processes, when they could benefit from sharing the heap on the same process. The Loom project started in 2017 and has undergone many changes and proposals. Virtual threads were initially called fibers, but later on they were renamed to avoid confusion.

• For example, data store drivers can be more easily transitioned to the new model.
• With Loom, the underlying carrier thread will continue executing other tasks while your virtual thread blocks.
• If I want to demonstrate the performance advantage of Virtual Threads over Platform Threads, I need to find a better use case.
• “Conservative was first — they are not looking to upset any of the existing Java programmers with features that are going to break a lot of what they do. But they are looking to do some innovation.”
• The use of synchronized code blocks is not in of itself a problem; only when those blocks contain blocking code, generally speaking I/O operations.
• “It’s interesting to see these competing models, and in general just getting improvements in the existing system.”

These two were marginally changed from their first appearance in Java 19 few months back, hence the content below is mostly the same as my last years Java 19 overview. Meaning if you are fully familiar with stuff introduced in 19 you’ll not see anything new in the coming paragraphs. Java 20 contained five more major JDK enhancement proposal updates under Projects Loom, Amber and Panama, and a few other Project Amber features were discussed as future roadmap items for Java 21.

Running Spring Applications on Virtual Threads

Virtual threads are one of the most important innovations in Java for a long time. They were developed in Project Loom and have been included in the JDK since Java 19 as a preview feature and since Java 21 as a final version (JEP 444). Dealing with sophisticated interleaving of threads (virtual or otherwise) is always going to be complex, and we’ll have to wait to see exactly what library support and design patterns emerge to deal with Loom’s concurrency model. Essentially, continuations allows the JVM to park and restart execution flow. The solution is to introduce some kind of virtual threading, where the Java thread is abstracted from the underlying OS thread, and the JVM can more effectively manage the relationship between the two. Project Loom sets out to do this by introducing a new virtual thread class.

Revision of Concurrency Utilities

Many applications make use of data stores, message brokers, and remote services. I/O-intensive applications are the primary ones that benefit from Virtual Threads if they were built to use blocking I/O facilities such as InputStream and synchronous HTTP, database, and message broker clients. Running such workloads on Virtual Threads helps reduce the memory footprint compared to Platform Threads and in certain situations, Virtual Threads can increase concurrency. Again we see that virtual threads are generally more performant, with the difference being most pronounced at low concurrency and when concurrency exceeds the number of processor cores available to the test.