One of the challenges of any new approach is how compatible it will be with existing code. Project Loom team has done a great job on this front, and Fiber can take the Runnable interface. To be complete, note that Continuation also implements Runnable. The following is a great image that depicts the choice that developers have to make today, between simple blocking / synchronous code and complex but scalable code.

Just as you almost never use LockSupport directly, so, too, you will never need to call Strand.park or Strand.unpark, unless you’re writing your own concurrency constructs . If you wish to turn off runaway fiber detection, set the co.paralleluniverse.fibers.detectRunawayFibers system property to”false”. A core component of Quasar, bytecode instrumentation, is a fork of the wonderful Continuations Library by Matthias Mann. Try hands-on activities in the OpenShift Sandbox Access Red Hat’s products and technologies without setup or configuration, and start developing quicker than ever before with our new, no-cost sandbox environments.

Communication Ministry promotes Palapa Ring Integration development – ANTARA English

Communication Ministry promotes Palapa Ring Integration development.

Posted: Tue, 01 Nov 2022 07:32:25 GMT [source]

Apart from Loom, the focus of this article, you should also keep an eye on Valhalla, which might double the performance of Java on some cases, and Graal, which does so many things that I don’t even know where to start! And of course, the language is becoming less verbose, thanks to Amber. JRebel skips redeploys and rebuilds while maintaining application state. This allows developers to instantly check the results of their code changes, allowing them to stay in rhythm while developing.


Continuations have a justification beyond virtual threads and are a powerful construct to influence the flow of a program. Project Loom includes an API for working with continuations, but it’s not meant for application development and is locked away in the jdk.internal.vm package. It’s the low-level construct that makes virtual threads possible. However, those who want to experiment with it have the option, see listing 3.

Vert.x is one such library that helps Java developers write code in a reactive manner. A Quasar Fiber is a Java Fiber that is used similar to a thread in the Java programming language. A Quasar will abstract both the implementations of a thread and Quasar Fiber in the Java programming language into a strand or simply a thick rope. This makes it convenient for the Fibers and Threads to co-operate without any disturbances. Let us think of a scenario where a Java application is started in the main thread.

So, instead of writing obj.getX(), or obj.x we write obj.get($x). What does this get us other than re-inventing what is a basic Java functionality, minus the some type safety? For example, among other things, we gain the ability to swap the implementation of the record or actor at runtime for maintenance (hot code-swapping). This can not only lead to code explosion; it can lead to bugs. The key to managing a complex state machine is by not handling messages in the order they arrive, but in the order we wish to process them. If your actor extends BasicActor, there’s another form of the receive method that allows for selective receive.

First, a fiber can have a return value of the generic type V (we’ll shortly see how to use it). If your fiber does not need to return a value, use Void as the type for V, and return null from the run method. Second, the run method is allowed to throw an InterruptedException, , as well as SuspendExecution which we’ll come back to. The wiki says Project Loom supports “easy-to-use, high-throughput lightweight concurrency and new programming models on the Java platform.” The scheduler allocates the thread to a CPU core to get it executed. In the modern software world, the operating system fulfills this role of scheduling tasks to the CPU.

Loom actor framework

It is possible to do so extending CustomActor or CustomActorWithResult, depending on the type of actor that you need. Another stated goal of Loom is Tail-call elimination (also called tail-call optimization). The core idea is that the system will be able to avoid allocating new stacks for continuations wherever possible.

As we will see, a thread is not an atomic construct, but a composition of two concerns — a scheduler and a continuation. Virtual threads may be new to Java, but they aren’t new to the JVM. Those who know Clojure or Kotlin probably feel reminded of “coroutines” (and if you’ve heard of Flix, you might think of “processes”). Those are technically very similar and address the same problem. However, there’s at least one small but interesting difference from a developer’s perspective.

java fiber

An excellent use case for actors is when you have a long-running task that is particularly light, typically because it relies on network operations and just waits for the clients to do something. For example, an IoT network might have all the devices permanently connected to a control server, sending messages only every now and then. A chat is another example of a program that can benefit from actors. And a server supporting WebSockets might be another candidate. As one of the reasons for implementing continuations as an independent construct of fibers is a clear separation of concerns. Continuations, therefore, are not thread-safe and none of their operations creates cross-thread happens-before relations.

So Aren’t JVM Fibers Generators or async/awaits?

When g returns, the code inserted in f will restore f’s local variables from the fiber stack. Transforming asynchronous code to fiber-blocking calls has a negligible overhead both in terms of memory and performance, while making the code shorter and far simpler to understand. In Java, each thread is mapped to an operating system thread by the JVM . With threads outnumbering the CPU cores, a bunch of CPU time is allocated to schedule the threads on the core.

java fiber

And if the memory isn’t the limit, the operating system will stop at a few thousand. In response to these drawbacks, many asynchronous libraries have emerged in recent years, for example using CompletableFuture. As have entire reactive frameworks, such as RxJava, Reactor, or Akka Streams.

Java fibers in action

When a child in the TRANSIENT mode dies, it will trigger a recovery event only if it has died as a result of an exception, but not if it has simply finished its operation. A TEMPORARY child never triggers it supervisor’s recovery event. The last behavior actor, the supervisor deserves a chapter of its own, as it’s at the core of the actor model’s error handling philosophy. Or by providing an instance of ServerHandler which implements these methods to the ServerActor constructor.

Please note that every generator is back by a thread / fiber, and while it can process millions of elements per second, it might still be slower than other solutions. In fact, I expect many cases to be covered with returning actors (e.g. you ask something to another actor and wait for the result), and they should be preferred. As an indication, Fibry can send around 7-8M of messages per second from a single core, under low thread contention. 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 . Loom proposes to move this limit towards million of threads.

java fiber

To obtain the value returned by the fiber , you call the get method, which joins the fiber and returns its result. Fibers in Quasar are scheduled by one or more ForkJoinPools. The easy and preferable way to instrument programs using Quasar is with the Java agent, which instruments code at runtime. When I run this program and hit the program with, say, 100 calls, the JVM thread graph shows a spike as seen below . The command I executed to generate the calls is very primitive, and it adds 100 JVM threads. Consider an application in which all the threads are waiting for a database to respond.

Java Partner Resources

This section will list the requirements of fibers and explore some design questions and options. It is not meant to be exhaustive, but merely present an outline of the design space and provide a sense of the challenges involved. The capitalized words Thread and Fiber would refer to particular Java classes, and will be used mostly when discussing the design of the API rather than of the implementation.

java fiber

It is, again, convenient to separately consider both components, the continuation and the scheduler. Again, threads — at least in this context — are a fundamental abstraction, and do not imply any programming paradigm. In particular, they refer only to the abstraction allowing programmers to write sequences of code that can run and pause, and not to any mechanism of sharing information among threads, such as shared memory or passing messages. JDK libraries making use of native code that blocks threads would need to be adapted to be able to run in fibers. The average time to accept a socket connection increased to about 3 ms. And the entire program takes about 5 minutes to run 😨. BTW,“Grep Console” is a great plugin to monitor output from the client and server println statements.

Project Loom

Unlike regular functions/objects, where an exception has to be caught and handled immediately on the callstack, with actors we can completely separate code execution from error handling. One of the reasons of providing a different receive function for actors is because programming with actors is conceptually different from project loom java just using fibers and channels. I think of channels as hoses pumping data into a function, or as sort of like asynchronous parameters. A fiber may pull many different kinds of data from many different channels, and combine the data in some way. Internally, a fiber is a continuation which is then scheduled in a scheduler.

QCon Software Development Conference

We will also learn how to use CircleCI, a continuous deployment tool, to automate testing and deployment. There are a few examples of distributed actors in the example package. Then, to make an actor discoverable cluster-wide, all you need to do is register it with the register method of the Actorclass.

Loom – Fibers, Continuations and Tail-Calls for the JVM

These projects might even change the perception of other languages, so they are potentially really high impact. Java is, and has been, a very popular language, attracting both praise and critique. While it would be fair to expect a decline after so many years and such a big legacy, Java is actually in pretty good shape and has a strong technical road-map ahead. A new era of Java is coming, and a few years from now, things might be very different in JVM-land. The OpenJDK has some technically impressive projects that we will hopefully be able to use soonish, and that have the potential to affect not only Java but even other languages.

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