Using Java’s Project Loom to build more reliable distributed systems

Creating such platform threads has always been costly , so Java has been using the thread pools to avoid the overhead in thread creation. The JVM gives an illusion of virtual threads, underneath whole story goes on platform threads. In the case of IO-work (REST calls, database calls, queue, stream calls etc.) this will absolutely yield benefits, and at the same time illustrates why they won’t help at all with CPU-intensive work . So, don’t get your hopes high, thinking about mining Bitcoins in hundred-thousand virtual threads.

  • A point to be noted is this suspension or resuming occurs in the application runtime instead of the OS.
  • When I ran this code and timed it, I got the numbers shown here.
  • Learn about Project Loom and the lightweight concurrency for JavaJVM.
  • Moving forward, we will call them platform threads, as well.
  • Candidates include Java server software like Tomcat, Undertow, and Netty; and web frameworks like Spring and Micronaut.
  • Virtual threads were initially called fibers, but later on they were renamed to avoid confusion.

A thread could be blocked from continuing if there is a delay in data to be read or written by an I/O task. 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. This comes with a lot of disadvantages that are heavyweight and context switching that is done by OS not by JVM. Introducing Loom we have a virtual thread that is managed by JVM. CPU is blocked until the current statement does not fully get executed even if that statement does not need the CPU.

Why are some Java calls blocking?

If a server has applied a log entry at a given index to its state machine, no other server will ever apply a different log entry for the same index. Subsystems could be tested in isolation against the simulation . You can reach us directly at or you can also ask us on the forum. For these situations, we would have to carefully write workarounds and failsafe, putting all the burden on the developer.

For example, there are many potential failure modes for RPCs that must be considered; network failures, retries, timeouts, slowdowns etc; we can encode logic that accounts for a realistic model of this. Project Loom provides ‘virtual’ threads as a first class concept within Java. There is plenty of good information in the 2020 blog post ‘State of Loom’ although details have changed in the last two years. The tests could be made extremely fast because the test doubles enabled skipping work.

Reasons for Using Java Project Loom

They built mocks of networks, filesystems, hosts, which all worked similarly to those you’d see in a real system but with simulated time and resources allowing injection of failures. Project Loom introduces lightweight and project loom java efficient virtual threads called fibers, massively increasing resource efficiency while preserving the same simple thread abstraction for developers. Another possible solution is the use of asynchronous concurrent APIs.

I think it simplifies reactive/concurrent programming in any JVM language. I think a Clojure with first class legitimate actor semantics would be unreal. Clojure core will espouse async and tell you why actors are bad but man I love the actor model. Right, but you’d still need to synchronize that with some concurrency primitives and that has the potential for bugs. Whereas on an immutable structure can’t suffer from that problem, which can make concurrent programming easier to reason about.

Difference between Platform Threads and Virtual Threads

Another big issue is that such async programs are executed in different threads so it is very hard to debug or profile them. In Java, Virtual threads (JEP-425) are JVM-managed lightweight threads that will help in writing high throughput concurrent applications . The JVM does delimited continuation on IO operations, no IO for virtual threads.

Reasons for Using Java Project Loom

With sockets it was easy, because you could just set them to non-blocking. However, operating systems also allow you to put sockets into non-blocking mode, which return immediately when there is no data availabel. And then it’s your responsibility to check back again later, to find out if there is any new data to be read. When you open up the JavaDoc of inputStream.readAllBytes() , it gets hammered into you that the call is blocking, i.e. won’t return until all the bytes are read – your current thread is blocked until then. What we potentially will get is performance similar to asynchronous, but with synchronous code.

1. Classic Threads or Platform Threads

These threads cannot handle the level of concurrency required by applications developed nowadays. For instance, an application would easily allow up to millions of tasks execution concurrently, which is not near the number of threads handled by the operating system. Notice the blazing fast performance of virtual threads that brought down the execution time from 100 seconds to 1.5 seconds with no change in the Runnable code. In this way, Executor will be able to run 100 tasks at a time and other tasks will need to wait. As we have 10,000 tasks so the total time to finish the execution will be approximately 100 seconds. Traditionally, Java has treated the platform threads as thin wrappers around operating system threads.

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I haven’t got any numbers on the rate of context switches per second, but it is certainly a great deal less than 2.5M/s. While I think reactive programming will fall out of favor, reactive-based libraries like Vert.X will still remain very popular even if the code you write with it isn’t reactive. There’s a reason why languages such as Golang and Kotlin choose this model of concurrency.

Single-threaded, reactive and Kotlin coroutine models

I feel like the unsung winner of Project Loom is going to be Clojure. It’s very slow, particularly since introducing byte weaving to introduce chaos in concurrency-sensitive places. Presently it takes a single thread in the region of twenty minutes to simulate a cluster from startup to shutdown, and to run a thousand linearisable operations .

Reasons for Using Java Project Loom

These access the store and mutate state in response to the requirements of the paper, they can be thought of as similar to any other HTTP API backed by a key-value store. Deepu is a polyglot developer, Java Champion, and OSS aficionado. He co-leads JHipster and created the JDL Studio and KDash. He is also an international speaker and published author. Cancellation propagation — If the thread running handleOrder() is interrupted before or during the call to join(), both forks are canceled automatically when the thread exits the scope. We can achieve the same functionality with structured concurrency using the code below.

I’ve done both actor model concurrency with Erlang and more reactive style concurrency with NodeJS. My experience is that the actor model approach is subjectively much better. If my experience is anything to go by then Loom will be awesome.

In comes Project Loom with virtual threads that become the single unit of concurrency. And now you can perform a single task on a single virtual thread. Java EE application servers improved the situation a lot, as implementations kept threads in a pool to be reused later.

Recruiting Developers – Why Finding the Right People Is So Important

Some, like CompletableFutures and Non-Blocking IO, work around the edges of things by improving the efficiency of thread usage. Others, like JavaRX , are wholesale asynchronous alternatives. 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. The implications of this for Java server scalability are breathtaking, as standard request processing is married to thread count. The downside is that Java threads are mapped directly to the threads in the OS.

Reasons for Using Java Project Loom

These costs are particularly high for distributed systems. Loom-driven simulations make much of this far simpler. As you build your distributed system, write your tests using the simulation framework. For shared datastructures that see accesses from multiple threads, one could write unit tests which check that properties are maintained using the framework.

Anyone have Project Loom leaks? 🙂

On their side, JetBrains has advertised Kotlin’s coroutines as being the easiest way to run code in parallel. By tweaking latency properties I could easily ensure that the software continued to work in the presence of e.g. RPC failures or slow servers, and I could validate the testing quality by introducing obvious bugs (e.g. if the required quorum size is set too low, it’s not possible to make progress). Certain parts of the system need some closer attention.

Future of Project Loom

If you’ve written the database in question, Jepsen leaves something to be desired. By falling down to the lowest common denominator of ‘the database must run on Linux’, testing is both slow and non-deterministic because most production-level actions one can take are comparatively slow. For a quick example, suppose I’m looking for bugs in Apache Cassandra which occur due to adding and removing nodes. It’s usual for adding and removing nodes to Cassandra to take hours or even days, although for small databases it might be possible in minutes, probably not much less than. I had an improvement that I was testing out against a Cassandra cluster which I discovered deviated from Cassandra’s pre-existing behaviour with probability one in a billion.

Already, Java and its primary server-side competitor Node.js are neck and neck in performance. An order of magnitude boost to Java performance in typical web app use cases could alter the landscape for years to come. This kind of control is not difficult in a language like JavaScript where functions are easily referenced and can be called at will to direct execution flow. Beyond this very simple example is a wide range of considerations for scheduling.

We also explored the tasks and schedulers in threads and how Fibers Class and pluggable user-mode schedulers can be an excellent alternative for traditional threads in Java. Project Loom allows the use of pluggable schedulers with fiber class. In asynchronous mode, ForkJoinPool is used as the default scheduler. It works on the work-stealing algorithm so that every thread maintains a Double Ended Queue of tasks. It executes the task from its head, and any idle thread does not block while waiting for the task. Instead, the task is pulled from the tail of the deque.

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