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July 04, 2021

July 04, 2021

July 04, 2021

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Spring into the Future: Embracing Virtual Threads with Java’s Project Loom

The second limitation is required for proper interaction with native code. Let us understand the difference between both kinds of threads when they are submitted with the same executable code. In Java, the final keyword is used to mark a variable, method, or class as immutable, meaning its value or behavior cannot be modified once it has been initialized. If you like this article, please like and share it with your friends and colleagues.

  • The code will create 10,000 virtual threads to complete these 10,000 tasks.
  • However, many server applications will choose virtual threads to achieve greater scalability.
  • The way we start threads is a little different since we’re using the ExecutorService.
  • In addition, this document provides an overview of how to install java and the environment variables you will need to set.
  • These platform-level threads are scheduled by the OS scheduler and the scheduling algorithm depends on the underlying OS.
  • In addition, Java 19 introduces the Executors.newThreadPerTaskExecutor method, which can take a ThreadFactory that builds virtual threads.
  • This can improve the scalability and efficiency of Java applications, particularly those that need to handle a large number of client connections or concurrent requests.

We very much look forward to our collective experience and feedback from applications. Our focus currently is to make sure that you are enabled to begin experimenting on your own. If you encounter specific issues in your own early experiments with Virtual Threads, please report them to the corresponding project. Virtual Threads impact not only Spring Framework but all surrounding integrations, such as database drivers, messaging systems, HTTP clients, and many more. Many of these projects are aware of the need to improve their synchronized behavior to unleash the full potential of Project Loom. As we can see, each thread stores a different value in the ThreadLocal, which is not accessible to other threads.

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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 will be production-ready in Java 21 . Because virtual threads are threads and have little new API surface of their own, there is relatively little to learn in order to use virtual threads. But there are actually quite a few things we need to unlearn in order to use them effectively. Virtual threads are fully compatible with the existing `Thread` API, so existing applications and libraries can support them with minimal change. Virtual threads are a lightweight implementation of Java threads, delivered as a preview feature in Java 19.

In our case, we have only one ContinuationScope object, the VTHREAD_SCOPE object. So, continuations execution is implemented using a lot of native calls to the JVM, and it’s less understandable when looking at the JDK code. However, we can still look at some concepts at the roots of virtual threads.

The thread-per-request style

We think that the future is bright for the JVM ecosystem and all the developers and languages part of this community after this upcoming change. Another change is the inclusion of a new ExecutorService, this new executor service can be instantiated by running Executors.newVirtualThreadPerTaskExecutor() method. There are some limitations currently with the use of synchronised blocks and thread locals, we won’t get into much details but the general recommendation is to avoid using them. The creation of Java threads is expensive because it involves allocating memory for the thread, initialising the thread stack and also making OS calls to register the OS thread. Lastly, but not less important, writing explicit asynchronous code is more error-prone due to the complexities that come with it. Currently, in the JDK, there is a one-to-one relationship between Java threads (also called “platform” threads) and OS threads.

virtual threads in java

The existing parity between OS threads and platform threads was a huge limitation factor for some applications due to the limit in the number of OS threads in a host. Virtual threads offer an exciting solution to improve performance and scalability for Spring developers. With little or no code changes required, it’s worth exploring how virtual threads can benefit your applications. Be sure to check out the Spring blog posts to learn more about embracing virtual threads and their performance analysis. Concurrent applications, those serving multiple independent application actions simultaneously, are the bread and butter of Java server-side programming. The thread has been Java’s primary unit of concurrency since its inception and is core to the entire Java platform.

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Virtual threads resolve one of the main problems with scalability in the JDK but how does it resolve it? The answer is, mainly, by breaking the association between a platform thread and an OS thread. A given request can be handled by multiple threads, therefore debugging, logging or analysing stack traces gets really difficult. In the last decade, we have tried to addressed this problem with the use of asynchronous processing libraries and the use of futures. For example, using CompletableFuture we can achieve a non-blocking approach, although the readability of these models is, in many cases, not what we would expect.

virtual threads in java

Now here we see the difference if you run the code then it will show the clear difference of up to 60 to 80% better performance. This is because virtual threads have better handling of IO-bound tasks, and can avoid the overhead of creating and destroying OS-level threads. One of the key benefits of virtual threads is their ability to reduce the cost of context switching. In traditional threads, a context switch requires the operating system to save and restore the state of the thread, which can be a costly operation. Virtual threads, on the other hand, are managed entirely by the JVM, so context switching is much faster and less expensive. The difference with virtual threads is that, due to them being under the control of the JVM, the thread stack is stored in the heap memory and not in the stack.

A point about performance

Unfortunately the JDK’s traditional thread dump, obtained with jstack or jcmd, presents a flat list of threads. This is suitable for dozens or hundreds of platform threads, but is unsuitable for thousands or millions of virtual threads. Richer relationships among threads can be shown when programs use structured concurrency.

virtual threads in java

Generate the project, open it in IntelliJ, and make sure the pom.xml file has maven-compiler-plugin configuration setup to enable the preview feature. Below is the FortuneRepository except the blocking we’ve seen earlier has been replaced by reactive methods. The vertx-sql-client is a reactive client, hence it is not supposed to block while waiting for the completion of a transaction with the database. However, when using the smallrye-mutiny-vertx-sqlclient it is possible to use a variant method that will await for the completion of the transaction, mimicking a blocking behaviour. It can be fairly easy to avoid these situations in our own code, but it is hard to verify every dependency we use.

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These platform-level threads are scheduled by the OS scheduler and the scheduling algorithm depends on the underlying OS. We’ve only included the latest elements and the final result for the sake of brevity, you can see how we are using platform threads from a cached thread pool. Every time that a virtual thread waits for IO, it yields to free its carrier thread. Once the IO operation gets completed, the virtual thread is put back into the FIFO queue of the ForkJoinPool and will wait until a carrier thread is available.

virtual threads in java

Developers should carefully evaluate the potential benefits and trade-offs of virtual threads before deciding whether to use them in their applications. Java Virtual Threads is a new feature introduced in Java 19 that allows developers to create lightweight threads, also known as fibers, that can run concurrently within a single operating system thread. This can improve the scalability and efficiency of Java applications, particularly those that need to handle a large number of client connections or concurrent requests.


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