Представление Project Loom в Java Хабр

It also may mean that you are overloading your database, or you are overloading another service, and you haven’t changed much. You just changed a single line that changes the way threads are created rather than platform, then you move to the virtual threads. Suddenly, you have to rely on these low level CountDownLatches, semaphores, and so on. I barely remember how they work, and I will either have to relearn them or use some higher level mechanisms. This is probably where reactive programming or some higher level abstractions still come into play.

So, if your task’s code does not block, do not bother with virtual threads. Most tasks in most apps are often waiting for users, storage, networks, attached devices, etc. An example of a rare task that might not block is something that is CPU-bound like video-encoding/decoding, scientific data analysis, or some kind of intense number-crunching. Such tasks should be assigned to platform threads directly rather than virtual threads. In case of Project Loom, you don’t offload your work into a separate thread pool, because whenever you’re blocked your virtual thread has very little cost. However, you will still be probably using multiple threads to handle a single request.

User Threads and Kernel Threads

This code creates 3K “sink threads” that simply discard the messages they receive. Let’s count how much time we need to create (and keep alive) 3K threads. You can try a higher number if your OS is properly tuned. I am using the standard configuration of a c5.2xlarge VM with Loom JDK without parameters.

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. Project Loom has made it into the JDK through JEP 425. It’s available since Java 19 in September 2022 as a preview feature. Its goal is to dramatically reduce the effort of writing, maintaining, and observing high-throughput concurrent applications.

Представление Project Loom в Java

This approach provides better usage (OS threads are always working and not waiting) and much less context switching. An unexpected result seen in the thread pool tests was that, more noticeably for the smaller response bodies, 2 concurrent users resulted in fewer average requests per second than a single user. Investigation identified that the additional delay occurred between the task being passed to the Executor and the Executor calling the task’s run() method. This difference reduced for 4 concurrent users and almost disappeared for 8 concurrent users.

Building responsiveness applications is a never-ending task. With the rise of powerful and multicore CPUs, more raw power is available for applications to consume. In Java, threads are used to make the application work on multiple tasks concurrently. A developer starts a Java thread in the program, and tasks are assigned to this thread to get processed. Threads can do a variety of tasks, such as read from a file, write to a database, take input from a user, and so on. Using a virtual thread based executor is a viable alternative to Tomcat’s standard thread pool.

Project Loom’s Virtual Threads

The core idea is that the system will be able to avoid allocating new stacks for continuations wherever possible. OS threads are at the core of Java’s concurrency model and have a very mature ecosystem around them, but they also come with some drawbacks and are expensive computationally. Let’s look at the two most common use cases for concurrency and the drawbacks of the current Java concurrency model in these cases. One core reason is to use the resources effectively. And hence we chain with thenApply etc so that no thread is blocked on any activity, and we do more with less number of threads. Loom is more about a native concurrency abstraction, which additionally helps one write asynchronous code.

One solution is making use of reactive programming. So, if a CPU has four cores, there may be multiple event loops but not exceeding to the number of CPU cores. This approach resolves the problem of context switching but introduces lots of complexity in the program itself. This type of project loom java program also scales better, which is one reason reactive programming has become very popular in recent times. Vert.x is one such library that helps Java developers write code in a reactive manner. This would be accomplished via virtual threads, delimited continuations and tail calls.

Synchronous Vs. Asynchronous

In particular, in most cases a Java programmer uses the Executors utility class to produce an ExecutorService. That executor service is backed by various kinds of thread factories or thread pools. I leave you with a few materials which I collected, more presentations and more articles that you might find interesting. Quite a few blog posts that explain the API a little bit more thoroughly.

• Also, the profile of your garbage collection will be much different.
• Much of this complexity is hidden from the user to make this code look simpler.
• Almost every blog post on the first page of Google surrounding JDK 19 copied the following text, describing virtual threads, verbatim.
• In this article, we’ll explain more about threads and introduce Project Loom, which supports high-throughput and lightweight concurrency in Java to help simplify writing scalable software.
• First, let’s see how many platform threads vs. virtual threads we can create on a machine.
• They are sleeping blocked on a synchronization mechanism, or waiting on I/O.

While things have continued to improve over multiple versions, there has been nothing groundbreaking in Java for the last three decades, apart from support for concurrency and multi-threading using OS threads. If you are doing the actual debugging, so you want to step over your code, you want to see, what are the variables? Because when your virtual thread runs, it’s a normal Java thread. It’s a normal platform thread because it uses carrier thread underneath.

Thread Sleep

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. That is what project Loom sets out to do, by introducing a new virtual thread class called a fiber. To give you a sense of how ambitious the changes in Loom are, current Java threading, even with hefty servers, is counted in the thousands of threads (at most). Loom proposes to move this limit towards million of threads. The implications of this for Java server scalability are breathtaking, as standard request processing is married to thread count.

This uses the newThreadPerTaskExecutor with the default thread factory and thus uses a thread group. When I ran this code and timed it, I got the numbers shown here. I get better performance when I use a thread pool with Executors.newCachedThreadPool(). Let’s look at some examples that show the power of virtual threads. Project Loom aims to drastically reduce the effort of writing, maintaining, and observing high-throughput concurrent applications that make the best use of available hardware. Java has long offered such throttling mechanisms.

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Erlang has native support for green threads, and in fact, the VM counts the operations and switch between green threads every now and then. «It would allow a web server to handle more requests at a given time while I/O bound, waiting for a database or another service,» Hellberg said. «Java is used very heavily on the back end in business applications, which is where we focus on helping businesses. … If we want to maintain and help people build new stuff, it’s important that the https://www.globalcloudteam.com/ language keeps up with that.» 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. Web servers like Jetty have long been using NIO connectors, where you have just a few threads able to keep open hundreds of thousand or even a million connections. An important note about Loom’s fibers is that whatever changes are required to the entire Java system, they are not to break existing code.