Virtual Threads: New Foundations for High-Scale Java Applications

If you have specific work that should be done in a platform thread (e.g. CPU-intensive work), nothing stops you from creating a platform thread for that. The stacks of virtual threads are stored in Java’s garbage-collected heap as stack chunk objects. The stacks grow and shrink as the application runs, both to be memory-efficient and to accommodate stacks of depth up to the JVM’s configured platform thread stack size. This efficiency is what enables a large number of virtual threads and thus the continued viability of the thread-per-request style in server applications. The thread dump is another popular tool for troubleshooting applications written in the thread-per-request style. Unfortunately the JDK’s traditional thread dump, obtained with jstack or jcmd, presents a flat list of threads.

• In the thread-per-task model, if you want to do two things sequentially, you just do them sequentially.
• You probably won’t even need to recompile and build new artefacts in some cases, because all of this is dealt with by the JDK runtime.
• The endpoints must now fetch all the fortunes in the database, then append a quote to each fortune before finally returning the result to the client.
• They extend the Thread class but are not tied to one specific OS thread.
• The introduction of Virtual Threads also prompts a broader revisit of decisions made for a runtime when only Platform Threads were available.
• They were very much a product of their time, when systems were single-core and OSes didnt have thread support at all.
• 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 .

Instead use constructs specifically designed for that purpose, such as semaphores. In conjunction with thread pools, developers sometimes use thread-local variables to share expensive resources among multiple tasks that share the same thread. For example, if a database connection is expensive to create then you can open it once and store it in a thread-local variable for later use by other tasks in the same thread.

Java Concurrency Utilities

Here on HappyCoders.eu, I want to help you become a better Java programmer.Read more about me here. By the way, you can find out if code is running in a virtual thread with Thread.currentThread().isVirtual(). Each platform thread had to process ten tasks sequentially, each lasting about one second.

Since most operations need not be atomic and are independent, this is not only more composable and evolvable, but also a more reasonable default. Implicit vs cooperative multithreading have pros and cons for each. These “let’s make our own threads” implementations all seem to stem from “I want threads, but I don’t want to wait for the kernel to do its thing”. Virtual threads don’t seem like a worthwhile complexity tradeoff unless you’re trying to run lots of threads in 32-bit address space. I wonder if this got started in that era and just took time to mature. The following page will illustrate how to get started with the maven build system in your java projects.

Intro to virtual threads: A new approach to Java concurrency

New methods in com.sun.jdi.request.ThreadStartRequest and com.sun.jdi.request.ThreadDeathRequest limit the events generated for the request to platform threads. Things would be very different if this program used an ExecutorService that creates a new platform thread for each task, such as Executors.newCachedThreadPool(). The ExecutorService would attempt to create 10,000 platform threads, and thus 10,000 OS threads, and the program might crash, depending on the machine and operating system. A virtual thread is an instance of java.lang.Thread that is not tied to a particular OS thread. A platform thread, by contrast, is an instance of java.lang.Thread implemented in the traditional way, as a thin wrapper around an OS thread. It is suggested that there is no need to replace synchronized blocks and methods that are used infrequently (e.g., only performed at startup) or that guard in-memory operations.

They get this name because they are managed by the platform they run on . Platform threads take up more memory because the JVM can’t grow and shrink the amount memory size of a platform thread. When a platform thread is created, the entire amount of memory that the thread can use is also allocated. Platform threads may end up with more memory than they would ever need. While virtual threads are the main course of Project Loom, there are several other Loom sub-projects that further enhance virtual threads.

Thread pool limit 10

In contrast, virtual threads are lightweight, which means that they require much less memory and processing resources. As you know, the JDK implements platform threads (java.lang.Thread) as thin wrappers around operating system threads. OS threads are expensive to create, and the number of threads is limited to the number of OS threads that the underlying hardware can support.

Existing tests will ensure that the changes we propose here do not cause unexpected regressions in the multitude of configurations and execution modes in which they are run. Virtual threads have no permissions when running with a SecurityManager set. A Thread.Builder can create either a thread or a ThreadFactory, which can then create multiple threads with identical java virtual threads example properties. A JDK Flight Recorder event is emitted when a thread blocks while pinned . The workload is not CPU-bound, since having many more threads than processor cores cannot improve throughput in that case. As a best practice, if a method is used very frequently and it uses a synchronized block then consider replacing it with the ReentrantLock mechanism.

Get support

And yes, it’s this type of I/O work where Project Loom will potentially shine. The aim of the tests was to verify how the application will utilize CPU, memory and threads during the load tests and if there is any difference between using the platform and virtual threads. Quarkus is a Java stack developed with cloud deployment in mind. It is Kubernetes-friendly and allows applications to be run on OpenJDK HotSpot and GraalVM.

If you don’t need this ability then you can use the fact that every “identity” having object in Java can be used as a lock with synchronized. While technically possible via some wizardry, its more straight forward in Java to make a helper method. If it were a situation with multiple “one shot” queues then CompletableFuture#anyOf and similar methods might suffice. One way around this is to send a special “sentinel” value over the queue to indicate that a reader should stop reading. This adds ExecutionException to the explicit list of things that can go wrong, but is a more direct api for a task that will run and produce one value as a result. In this case we just choose to throw a RuntimeException to indicate we just want to crash.

How to Create a Virtual Thread

Not every application will benefit from a big performance improvement after having adopted virtual threads. We will only observe a huge benefit when our application is IO-bound. In this article we will try to give you a solid background about why Java virtual threads are very needed in the JVM ecosystem and mainly, provide you with the basics to be able to understand Java virtual threads. The JDK can now run up to 10,000 concurrent virtual threads on a small number of operating system threads, as little as one, to execute the simple code above that involves sleeping for one second. With this virtual thread, we get all the benefits traditional threads have, plus it is cheap, lightweight, and virtually free.