Loom threads have the same basic semantics as normal threads. There’s nothing special about them that relates to immutability. Stardog, enterprise knowledge graph platform, (stardog.com), is an early adopter of Antithesis and we’ve found it to be very helpful in HA Cluster, distributed consensus, etc. So, I’m not sure it has affected the speed or ease of shipping improvements, rather than enabled a class of work that would have previously been impossible to do safely .

I’ve found Jepsen and FoundationDB to apply two similar in idea but different in implementation testing methodologies in an extremely interesting way. Java’s Project Loom makes fine grained control over execution easier than ever before, enabling a hybridized approach to be cheaply project loom java invested in. Historically this approach was viable, but a gamble, since it led to large compromises elsewhere in the stack. I think that there’s room for a library to be built that provides standard Java primitives in a way that can admits straightforward simulation .

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Java Champion James Ward on the State of Java and JVM Languages.

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From an OS perspective, you are spawning only a few threads but in terms of the programming language or JVM, you are using many threads. Asynchronous calls will overcome most of the problems https://globalcloudteam.com/ of synchronous calls like scaling which is an important factor of any application in the current world. But it has its disadvantages like it is difficult to write and debug it.

Java Virtual Threads – Project Loom

You can still use a fixed thread pool with a custom task scheduler if you like, but probably not exactly what you are after. If everyone was clamoring for Java and settled on Go only because of goroutines, then sure, but I think Go was liked for a lot of reasons aside from that. I also don’t often see people complain about wanting more control over the scheduler for Go . That doesn’t solve the problem in parallel contexts, only for concurrent ones.

Reasons for Using Java Project Loom

This places a hard limit on the scalability of concurrent Java apps. Not only does it imply a one-to-one relationship between app threads and operating system threads, but there is no mechanism for organizing threads for optimal arrangement. For instance, threads that are closely related may wind up sharing different processes, when they could benefit from sharing the heap on the same process.

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And so, even if we try to change the priority of a virtual thread, it will stay the same. Obviously, those times are really hardware dependant, but those will be used as a reference to compare to the other running scenarios. However, forget about automagically scaling up to a million of private threads in real-life scenarios without knowing what you are doing. I maintain some skepticism, as the research typically shows a poorly scaled system, which is transformed into a lock avoidance model, then shown to be better. I have yet to see one which unleashes some experienced developers to analyze the synchronization behavior of the system, transform it for scalability, then measure the result.

Reasons for Using Java Project Loom

Loom is going to leapfrog it and remove pretty much all downsides. 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.

Simulation performance

But this pattern limits the throughput of the server because the number of concurrent requests becomes directly proportional to the server’s hardware performance. So, the number of available threads has to be limited even in multi-core processors. The entire point of virtual threads is to keep the “real” thread, the platform host-OS thread, busy. With Loom, now you have M green threads mapped to N kernel threads. These green threads are way cheaper to spawn, so you could have thousands (millions even?) of green threads.

Reasons for Using Java Project Loom

Generics took forever to implement, aren’t even feature complete , and have no integration with the standard lib. Meanwhile Java is adding lots of new features and versions at a quick pace. Channels are just blocking queues with weirder semantics. It might be equally accessible, but mutable collections require you import classes from scala.collection.mutable that have very different names, e.g., mutable.ArrayBuffer vs List.

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Under the hood, asynchronous acrobatics are under way. Why go to this trouble, instead of just adopting something like ReactiveX at the language level? The answer is both to make it easier for developers to understand, and to make it easier to move the universe of existing code. For example, data store drivers can be more easily transitioned to the new model. Note that after using the virtual threads, our application may be able to handle millions of threads, but other systems or platforms handle only a few requests at a time.

  • When to use are obvious in textbook examples; a little less so in deeply nested logic.
  • 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.
  • Non-standard tools are half-baked, inconsistently maintained and not ready for primetime.
  • You almost always need heap allocations, especially for long running, large apps — and Java has the state of the art GC implementation on both throughput and low-latency front.
  • A thread supports the concurrent execution of instructions in modern high-level programming languages and operating systems.
  • Many races will only be exhibited in specific circumstances.

With loom, there isn’t a need to chain multiple CompletableFuture’s . And with each blocking operation encountered (ReentrantLock, i/o, JDBC calls), the virtual-thread gets parked. And because these are light-weight threads, the context switch is way-cheaper, distinguishing itself from kernel-threads.

Also, JavaRX can’t match the theoretical performance achievable by managing virtual threads at the virtual machine layer. Project Loom tries to solve the problem of asynchronous and synchronous calls. It will be easy to write and debug the code with Loom that is Scalable, asynchronous, and lightweight.


Traditional Java threads have served very well for a long time. With the growing demand of scalability and high throughput in the world of microservices, virtual threads will prove a milestone feature in Java history. In the following example, we are submitting 10,000 tasks and waiting for all of them to complete.

StructuredTaskScope also ensures the following behavior automatically. Imagine that updateInventory() is an expensive long-running operation and updateOrder() throws an error. The handleOrder() task will be blocked on inventory.get() even though updateOrder() threw an error. Ideally, we would like the handleOrder() task to cancel updateInventory() when a failure occurs in updateOrder() so that we are not wasting time.

Reasons for Using Java Project Loom

These mechanisms are not set in stone yet, and the Loom proposal gives a good overview of the ideas involved. Fibers are designed to allow for something like the synchronous-appearing code flow of JavaScript’s async/await, while hiding away much of the performance-wringing middleware in the JVM. As a best practice, if a method is used very frequently and it uses a synchronized block then consider replacing it with the ReentrantLock mechanism.

Virtual threads are produced over the heavyweight kernel thread. It means that from one kernel thread we can produce many virtual threads. The number of threads created by the Executor is unbounded. We can use the Thread.Builder reference to create and start multiple threads. Executer service can be created with virtual thread factory as well, just putting thread factory with it constructor argument.

Using the simulation to improve protocol performance

With over 20 years of experience, he does work for private, educational, and government institutions. He is also currently a speaker for No Fluff Just Stuff tour. Daniel loves JVM languages like Java, Groovy, and Scala; but also dabbles with non JVM languages like Haskell, Ruby, Python, LISP, C, C++.

New methods in Thread Class

The project is currently in the final stages of development and is planned to be released as a preview feature with JDK19. Project Loom is certainly a game-changing feature from Java so far. This new lightweight concurrency model supports high throughput and aims to make it easier for Java coders to write, debug, and maintain concurrent Java applications. With virtual thread, a program can handle millions of threads with a small amount of physical memory and computing resources, otherwise not possible with traditional platform threads. It will also lead to better-written programs when combined with structured concurrency. Apart from the number of threads, latency is also a big concern.

To give some context here, I have been following Project Loom for some time now. On the opposite, after having invested so much effort in their respective frameworks, they decide to continue as if nothing happened. For example, the Spring framework took care of actually designing a shared Reactive API called Reactive Streams, with no Spring dependencies. There are currently two implementations, RxJava v2 and Pivotal’s Project Reactor.

Java does not make it easy to control the threads , and so influencing the interleaving of execution is very difficult except for in very isolated cases. FoundationDB’s usage of this model required them to build their own programming language, Flow, which is transpiled to C++. The simulation model therefore infects the entire codebase and places large constraints on dependencies, which makes it a difficult choice. Jepsen is probably the best known example of this type of testing, and it certainly moved the state of the art; most database authors have similar suites of tests. ScyllaDB documents their testing strategy here and while the styles of testing might vary between different vendors, the strategis have mostly coalesced around this approach.