Sharing data across the actors in the connected workflow is traditionally done via passing it as method arguments, but one way to not clutter your code with plethora of method parameters is to use Thread Local variables for data scoped within a running thread. The most used example for thread per workload pattern are certainly web servers that are listening for internet traffic and spanning a new thread for every separate request. Assumptions leading to the asynchronous Servlet API are subject to be invalidated with the introduction of Virtual Threads. The async Servlet API was introduced to release server threads so the server could continue serving requests while a worker thread continues working on the request. This makes lightweight Virtual Threads an exciting approach for application developers and the Spring Framework. Past years indicated a trend towards applications that communicate over the network with each other.

java loom

Although RXJava is a powerful and potentially high-performance approach to concurrency, it has drawbacks. In particular, it is quite different from the conceptual models that Java developers have traditionally used. Also, RXJava can’t match the theoretical performance achievable by managing virtual threads at the virtual machine layer. Before looking more closely at Loom, let’s note that a variety of approaches have been proposed for concurrency in Java. Some, like CompletableFutures and non-blocking IO, work around the edges by improving the efficiency of thread usage. Others, like RXJava (the Java implementation of ReactiveX), are wholesale asynchronous alternatives.

The best way to handle API responses in Spring Boot

Structured concurrency aims to simplify multi-threaded and parallel programming. It treats multiple tasks running in different threads as a single unit of work, streamlining error handling and cancellation while improving reliability and observability. Being an incubator feature, this might go through further changes during stabilization. First, let’s see how many platform threads vs. virtual threads we can create on a machine.

My machine is Intel Core i H with 8 cores, 16 threads, and 64GB RAM running Fedora 36. Virtual threads are lightweight threads that are not tied to OS threads but are managed by the JVM. They are suitable for thread-per-request programming styles without having the limitations of OS threads. This is quite similar to coroutines, like goroutines, made famous by the Go programming language (Golang).

Virtual threads

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. We are doing everything we can to make the preview experience as seamless as possible for the time being, and we expect to provide first-class configuration options once Loom goes out of preview in a new OpenJDK release.

java loom

If the stack gets parked on the heap when unmounted and moved back onto the stack when mounted, it could end up at a different memory address. Each of these individual things, Project Loom, and GraalVM native images, offer compelling runtime characteristics. Beyond this very simple example is a wide range of considerations for scheduling. These mechanisms are not set in stone yet, and the Loom proposal gives a good overview of the ideas involved. See the Java 21 documentation to learn more about structured concurrency in practice.

Estimate Your Project

The implementation becomes even more fragile and puts a lot more responsibility on the developer to ensure there are no issues like thread leaks and cancellation delays. Building up on the previous topic Structured Concurrency works perfectly with virtual threads, where virtual threads deliver an abundance of threads and structured concurrency ensures that they are correctly and robustly coordinated. The second potential pitfall is the lifetime of the data when the request is not short lived. For long running requests when you are storing heavy / expensive data in ThreadLocal storage you’ll might want to release the data as soon as it’s not needed any more. The API allows you to free the data manually while the thread is still running by calling the remove() method.

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