Another possible solution is the use of asynchronous concurrent APIs. CompletableFuture and RxJava are quite commonly used APIs, to name a few. These APIs do not block the thread in case of a delay. Instead, it gives the application a concurrency construct over the Java threads to manage their work.

I may be wrong, but as far as I understand, the whole Reactive/Event Loop thing, and Netty in particular, was invented as an answer to the C10K+ problem. It has obvious drawbacks, as all your code now becomes Async, with ugly callbacks, meaningless stack traces, and therefore hard to maintain and to reason about. Java runtimes and frameworks Deploy your application safely and securely into your production environment without system or resource limitations.

Netty And Project Loom

Learning paths Customize your learning to align with your needs and make the most of your time by exploring our massive collection of paths and lessons. The difference between Reactor and Loom, similar to using java8 Stream API. I am now using Reactor to build a reactive system, and to a certain extent using Kotlin Coroutine. My guess is that there would not be any difference w.r.t performance. And then when it’s available, most projects will still be stuck waiting to make the jump from Java 8 to 11 first… Making statements based on opinion; back them up with references or personal experience.

project loom vs reactive

It’s often easier to write synchronous code because you don’t have to keep writing code to put things down and pick them back up every time you can’t make forward progress. Straightforward «do this, then do that, if this happens do this other thing» code is easier to write than a state machine updating explicit state. Virtual threads can give you most of the benefits of asynchronous code while your coding experience is much closer project loom to that of writing synchronous code. Project Looms changes the existing Thread implementation from the mapping of an OS thread, to an abstraction that can either represent such a thread or a virtual thread. In itself, that is an interesting move on a platform that historically put a lot more value on backward-compatibility in comparison to innovation. Compared to other recent Java versions, this feature is a real game-changer.

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. For coroutines, there are special keywords in the respective languages (in Clojure a macro for a «go block», in Kotlin the «suspend» keyword). The virtual threads in Loom come without additional syntax.

This approach provides better usage and much less context switching. Consider an application in which all the threads are waiting for a database to respond. Although the application computer is waiting for the database, many resources are being used on the application computer.

It brings a new lightweight construct for concurrency, named virtual threads. Project Loom offers a much-suited solution for such situations. It proposes that developers could be allowed to use virtual threads using traditional blocking I/O. This could easily eliminate scalability issues due to blocking I/O. In the context of virtual threads, “channels” are particularly worth mentioning here.

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There’s a reason why languages such as Golang and Kotlin choose this model of concurrency. Go’s language with goroutines was a solution, now they can write Sync code and also handle C10K+. So now Java comes up with Loom, which essentially copies the Go’s solution, soon we will have Fibers and Continuations and will be able to write Sync code again.

We have seen this repeatedly on how abstraction with syntactic sugar, makes one effectively write programs. Whether it was FunctionalInterfaces in JDK8, for-comprehensions in Scala. Async/await in c# is 80% there – it still invades your whole codebase and you have to be really careful about not blocking, but at least it does not look like ass. Loom is going to leapfrog it and remove pretty much all downsides. Finally, for the same reason, traditional stack traces not helpful. For a complete list of options, check this document.

I would say Project Loom brings similar capability as goroutines and allows Java programmers to write internet scale applications without reactive programming. However, it doesn’t block the underlying native thread, which executes the virtual thread as a “worker”. Rather, the virtual thread signals that it can’t do anything right now, and the native thread can grab the next virtual thread, without CPU context switching. But how can this be done without using asynchronous I/O APIs? After all, Project Loom is determined to save programmers from “callback hell”. On the contrary, Virtual threads, also known as user threads or green threads are scheduled by the applications instead of the operating system.

In Java, parallelism is done using parallel streams, and project Loom is the answer to the problem with concurrency. In this article, we will be looking into Project Loom and how this concurrent model works. We will be discussing the prominent parts of the model such as the virtual threads, Scheduler, Fiber class and Continuations. One core reason is to use the resources effectively.

The Best Ides For Reactive Native Apps: 5 Popular Examples

For instance, Thread.ofVirtual() method that returns a builder to start a virtual thread or to create a ThreadFactory. Similarly, the Executors.newVirtualThreadPerTaskExecutor() method has also been added, which can be used to create an ExecutorService that uses virtual threads. You can use these features by adding –enable-preview JVM argument during compilation and execution like in any other preview feature.

project loom vs reactive

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Vert.x is one such library that helps Java developers write code in a reactive manner. Is it possible to combine some desirable characteristics of the two worlds? Be as effective as asynchronous or reactive programming, but in a way that one can program in the familiar, sequential command sequence? Oracle’s Project Loom aims to explore exactly this option with a modified JDK.

The sole purpose of this addition is to acquire constructive feedback from Java developers so that JDK developers can adapt and improve the implementation in future versions. Virtual threads, as the primary part of the Project loom, are currently targeted to be included in JDK 19 as a preview feature. If it gets the expected response, the preview status of the virtual threads will then be removed by the time of the release of JDK21. Few new methods are introduced in the Java Thread class.

Beyond Virtual Threads

This limits the working of threads and the number of threads an application can utilize. As a result, concurrent connections would also get limited due to which threads could not be appropriately scaled. Note that this leaves the PEA divorced from the underlying system thread, because they are internally multiplexed between them. This is your concern about divorcing the concepts. In practice, you pass around your favourite languages abstraction of a context pointer.

project loom vs reactive

What we potentially will get is performance similar to asynchronous, but with synchronous code. Lightweight, modular, and extensible library for functional programming. I tried getting into it with Quarkus (Vert.x) and it was a nightmare. Kept running into not being able to block on certain threads. There are a few different patterns and approaches to learn, but a lot of those are way easier to grasp and visualize over callback wiring.


Developers in general should start getting familiar with it as soon as possible. Developers who are about to learn about Reactive and coroutines should probably take a step back, and evaluate whether they should instead learn the new Thread API – or not. Both frameworks will continue their lives, but change their respective underlying implementation to use virtual threads.

With Loom, we write synchronous code, and let someone else decide what to do when blocked. LibHunt tracks mentions of software libraries on relevant social networks. Based on that data, you can find the most popular open-source packages, as well as similar and alternative projects.

Lock avoidance makes that, for the most part, go away, and be limited to contended leaf components like malloc(). And debugging is indeed painful, and if one of the intermediary stages results with an exception, the control-flow goes hay-wire, resulting in further code to handle it. With Loom, a more powerful abstraction is the savior.

As 1 indicates, there are tangible results that can be directly linked to this approach; and a few intangibles. Locking is easy — you just make one big lock around your transactions and you are good to go. That doesn’t scale; but fine-grained locking is hard. Hard to get working, hard to choose the fineness of the grain. When to use are obvious in textbook examples; a little less so in deeply nested logic.

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