QCon Plus Online May 10-20, 2022 Session Project Loom: Revolution in Java Concurrency or Obscure Implementation Detail?

Internally, it was doing all this back and forth switching between threads, also known as context switching, it was doing it for ourselves. Another reason to avoid virtual threads is with existing code that depends on the limits or bottlenecks of platform threads to throttle their app’s usage of other resources. For example, if a database server is limited to 10 simultaneous connections, then some app have been written to use an executor service backed by only 8 or 9 threads. Such existing code should not be blindly switched to virtual threads. A virtual thread looks the same as the threads we are already familiar with in Java, but they work differently.

Advanced Java topics, algorithms and data structures. After that, the program no longer needs 10 seconds but only just over one second. It can hardly be faster because every task waits one second. Virtual Threads impact not only Spring Framework but all surrounding integrations, such as database drivers, messaging systems, HTTP clients, and many more. Many of these projects are aware of the need to improve their synchronized behavior to unleash the full potential of Project Loom. There is a re-implementation of the expressjs API in Java using LoomJExpressLoom.java.

In this article, author discusses data pipeline and workflow scheduler Apache DolphinScheduler and how ML tasks are performed by Apache DolphinScheduler using Jupyter and MLflow components. Susanne Kaiser is a software consultant working with teams on microservice adoption. Recently, she’s brought together Domain-Driven Design, Wardley Mapping, and Team Topologies into a conversation about helping teams adopt a fast flow of change.

Observability — A thread dump would clearly display the task hierarchy, with the threads running updateInventory() and updateOrder() shown as children of the scope. 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.

Why Use Project Loom?

QCon Plus Make the right decisions by uncovering how senior software developers at early adopter companies are adopting emerging trends. Like any ambitious new project, Loom is not without its challenges. Dealing with sophisticated interleaving of threads is always going to be a complex challenge, and we’ll have to wait to see exactly what library support and design patterns emerge to deal with these situations. At a high level, a continuation is a representation in code of the execution flow. In other words, a continuation allows the developer to manipulate the execution flow by calling functions. The Loom docs present the example seen in Listing 3, which provides a good mental picture of how this works.

Disappointed with the quality of software written these days (so often by himself!), hates long methods and hidden side… When you create a new Thread in Java a system call is done to the OS telling it to create a new system thread. Creating a system thread is expensive because the call takes up much time, and each thread takes up some memory. Your threads also share the same CPU, so you don’t want them to block it, causing other threads to wait unnecessarily. As the suspension of a continuation would also require it to be stored in a call stack so it can be resumed in the same order, it becomes a costly process.

Project Loom Comparison

Then we move on, and in line five, we run the continuation once again. Not really, it will jump straight to line 17, which essentially means we are continuing from the place we left off. Also, it means we can https://globalcloudteam.com/ take any piece of code, it could be running a loop, it could be doing some recursive function, whatever, and we can all the time and every time we want, we can suspend it, and then bring it back to life.

• 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.
• QCon Plus Make the right decisions by uncovering how senior software developers at early adopter companies are adopting emerging trends.
• There’s a list of APIs that do not play well with Project Loom, so it’s easy to shoot yourself in the foot.
• Java has had good multi-threading and concurrency capabilities from early on in its evolution and can effectively utilize multi-threaded and multi-core CPUs.
• The suspend method allows passing information from the yield point to the continuation , and back from the continuation to the suspension point .

JDK libraries making use of native code that blocks threads would need to be adapted to be able to run in fibers. In particular this implies changing the java.io classes. 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. In the thread-per-request model with synchronous I/O, this results in the thread being “blocked” for the duration of the I/O operation. The operating system recognizes that the thread is waiting for I/O, and the scheduler switches directly to the next one.

Revision of Concurrency Utilities

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. Another question is whether we still need reactive programming.

There’s nothing really exciting here, except from the fact that the foo function is wrapped in a continuation. Wrapping up a function in a continuation doesn’t really run that function, it just wraps a Lambda expression, nothing specific to see here. However, if I now run the continuation, so if I call run on that object, I will go into foo function, and it will continue running.

Especially when you look at earlier examples like this one, where you could use CompletableFuture.stream. Those methods are no longer available, so we have to do something else. I’m no native code guy, in fact I can’t even write C or C++.

This includes thread pools, executors, and, to some degree, various reactive and asynchronous programming techniques. Not all these will be gone with Project Loom , but for sure we’ll have to rethink our approach to concurrency in a number of places. Project Loom addresses just a tiny fraction of the problem, it addresses asynchronous programming.

When to Install New Java Versions

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. Although JavaRX is a powerful and potentially high-performance approach to concurrency, it is not without drawbacks.

Examples include hidden code, like loading classes from disk to user-facing functionality, such as synchronized and Object.wait. It is also possible to split the implementation of these two building-blocks of threads between the runtime and the OS. Splitting the implementation the other way — scheduling by the OS and continuations by the runtime — seems to have no benefit at all, as it combines the worst of both worlds. 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.

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. While virtual threads won’t magically run everything faster, benchmarks run against the current early access builds do indicate that you can obtain similar project loom java scalability, throughput, and performance as when using asynchronous I/O. In the second variant, Thread.ofVirtual() returns a VirtualThreadBuilder whose start() method starts a virtual thread. The alternative method Thread.ofPlatform() returns a PlatformThreadBuilder via which we can start a platform thread.

What Are Threads In Java? What are Virtual Threads?

We’re just at the start of a discussion as to how to further evolve our effect systems. There’s been a hot exchange on that topic on the Scala Contributors forum, you can find the summary over here. Another interesting related presentation is Daniel Spiewak’s “Case for effect systems” where he argues that Loom obsoletes Future, but not IO. As mentioned earlier, proper sequencing needs a bit more mindfulness in the Loom than the ZIO implementation so that at one point, we don’t inadvertently run the side-effects at the moment of their construction.

Blocking operations thus no longer block the executing thread. This allows us to process a large number of requests in parallel with a small pool of carrier threads. For example, if a request takes two seconds and we limit the thread pool to 100 threads, then a maximum of 50 requests per second could be answered. However, the CPU would be far from being utilized since it would spend most of its time waiting for responses from the external services, even if several threads are served per CPU core.

Why Do We Need Virtual Threads?

The frontend web server receives connections and requests from ApacheBench. For each request received, it makes three calls in succession to the backend web server. Each backend call has a configured latency of 1/3 seconds, so the target latency at the frontend web server is 1 second.

It is required due to the high frequency of threads working concurrently. Hence, context switching takes place between the threads, which is an expensive task affecting the execution of the application. A thread supports the concurrent execution of instructions in modern high-level programming languages and operating systems.

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Others, like JavaRX , are wholesale asynchronous alternatives. You can use this guide to understand what Java’s Project loom is all about and how its virtual threads (also called ‘fibers’) work under the hood. But why would user-mode threads be in any way better than kernel threads, and why do they deserve the appealing designation of lightweight? It is, again, convenient to separately consider both components, the continuation and the scheduler. As there are two separate concerns, we can pick different implementations for each. Currently, the thread construct offered by the Java platform is the Thread class, which is implemented by a kernel thread; it relies on the OS for the implementation of both the continuation and the scheduler.