Simple paradigms of concurrency will be adopted after this change is made available in one of the next JDK releases. One last thing that we wanted to mention is that virtual threads also opens the door to introduce structured concurrency in Java. This change will also make Java code much safer when running multiple concurrent tasks at different nested levels. If you were wondering what would happen to your code after migrating to Java 19 if it uses synchronized blocks or any of the traditional concurrency mechanisms, there’s good news. The old concurrent code will work with virtual threads without having to modify it at all.

It would split the world between APIs designed for threads and APIs designed for coroutines, and would require the new thread-like construct to be introduced into all layers of the platform and its tooling. This would take longer for the ecosystem to adopt, and would not be as elegant and harmonious with the platform as user-mode threads. A new command allows debuggers to test if a thread is a virtual thread. Scoped values may prove to be a better alternative to thread locals for some use cases. The workload is not CPU-bound, since having many more threads than processor cores cannot improve throughput in that case. I think that programmers won’t use Loom directly on a daily basis.

Why Use Virtual Threads?

Carrier threadA platform thread used to execute a virtual thread is called a carrier. This isn’t a class distinct from Thread or VirtualThread but rather a functional denomination. This is the reference guide for using virtual threads to write reactive REST services. Please refer to the Writing JSON REST services guides for a lightweight introduction to reactive REST services and to the Writing REST Services with RESTEasy Reactive guide for a detailed presentation. Blocking a virtual thread results in yielding its continuation and unparking it results in the continuation being resubmitted to the scheduler. Because the Java runtime can explicitly control when a virtual thread is suspended and resumed, that structure allows a more fine-grained concurrency model for Java.

Such a factory can be obtained with Thread.ofVirtual().factory(). There are other ways of using Thread to spawn virtual threads, like Thread.ofVirtual().start. https://globalcloudteam.com/ Nearly all blocking points in the JDK were made aware of virtual threads, and will unmount a virtual thread rather than blocking it.

Detailed changes

From the output, we understand that the same virtual thread jumps from one platform thread it was running in at the beginning to another when it comes back from sleeping. Project Loom is still an experimental feature and is not available in stable Java releases. JDK 21, which is still not released, is expected to include virtual threads. In a server application, a thread is assigned to each incoming request.

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. In other cases, the changes will be minimal to take full advantage of virtual threads. It’s worth mentioning that the underlying platform threads, also called carrier threads in terms of scheduling, are still managed by the OS scheduler. They’re now a layer of abstraction completely invisible to the developer writing concurrent code. The JDK scheduler does not use time slices, in this case is the virtual thread itself who will yield and renounce to its carrier thread when it’s waiting for a blocking operation response.

Running the application

Project Loom aims to mitigate or solve said problems by introducing virtual threads. Considering multitasking in an OS with a multicore CPU, all of the threads must compete over access to the hardware resources. This leads to many problems that must be resolved to effectively use the multitasking concept, thread locking, thread scheduling, synchronization, to name a few. Typically, the polling thread cannot be a virtual thread, and the consumer could with some work to make sure that we do not pin or monopolize the carrier thread. According to this article thread local will still be an instance local to the currently executing virtual thread. Virtual threads are a new kind of thread added as a preview feature to Java 19.

Virtual threads help to improve the throughput of typical server applications precisely because such applications consist of a great number of concurrent tasks that spend much of their time waiting. Today, every instance of java.lang.Thread in the JDK is a platform thread. A platform thread runs Java code on an underlying OS thread and captures the OS thread for the code's entire lifetime. The number of platform threads is limited to the number of OS threads. 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. It is Kubernetes-friendly and allows applications to be run on OpenJDK HotSpot and GraalVM.

Java Reflection API & How Spring uses Reflection.

It can be fairly easy to avoid these situations in our own code, but it is hard to verify every dependency we use. Typically, while experimenting with virtual-threads, we realized that using the postgresql-JDBC driverresults in frequent pinning. That is what happens when a virtual thread was suspended and later resumed.