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vert-x3 vertx-virtual-threads-incubator: Vert x virtual threads incubator

By April 3, 2021November 16th, 202292 Comments

These methods throw an exception when invoked on a virtual thread. Since virtual threads are implemented in the JDK and are not tied to any particular OS thread, they are invisible to the OS, which is unaware of their existence. OS-level monitoring will observe that a JDK process uses fewer OS threads than there are virtual threads. Let’s start with the challenge that led to the development of virtual threads.

virtual threads

From what I know the loom project was started a few years ago, perhaps in 2019. Java Reactive works around the shortcomings of the platform by basically inventing its own language inside Java. Language runtimes have been taking over that role over the last few decades, sure. However, whether or not unikernels are the way forward remains to be seen. There’s a lot of people who advocate otherwise, but I don’t think we have the mechanisms for effect polymorphism in current languages good enough to make effects ergonomic. After years of using the library that inspired this , I’m so stoked this is coming to the wide outside world of Java.

Differences between virtual threads and platform threads

You can see that there are many virtual threads running by the same “carrier” thread, for example, on the ForkJoinPool-1-worker-9. We use an implementation of the SmallRye Mutiny client for Postgres. The PgPool client allows us to create and execute SQL queries in a non-blocking way. In order to create a query, we should call the preparedQuery method. Finally, we need to invoke the executeAndAwait method to perform the operation asynchronously.

virtual threads

Their state is simply stored in the heap and another Virtual thread is executed on the same Java platform thread. Virtual threads offer some significant advantages that async/await does not. Virtual threads are not just syntactic sugar for an asynchronous framework, but an overhaul to the JDK libraries to be more “blocking-aware”. Without that, an errant call to a synchronous blocking method from an async task will still tie up a platform thread for the duration of the call.

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We had to change low-level I/O in the JDK because it drops down to native. This blog post teaches you how to use the new module vertx-web-api-service to combine the Web Router and the OpenAPI Router Factory with service proxies. Yes, if they can do the same for Project Leyden , jvm would be the best platform for cloud and serverless.

Java News Roundup: OpenJDK Updates, JDK 20 Release Schedule, GraalVM 22.3, JReleaser 1.3.0 –

Java News Roundup: OpenJDK Updates, JDK 20 Release Schedule, GraalVM 22.3, JReleaser 1.3.0.

Posted: Mon, 31 Oct 2022 07:00:00 GMT [source]

If the JDK is compatible then the endpoint will be offloaded to a virtual thread. It will then be possible to perform blocking operations without blocking the platform thread upon which the virtual thread is mounted. We now know that we can create way more virtual threads than platform threads. One could be tempted to use virtual threads to perform long computations (CPU-bound workload).

Project Loom Experiment using Spring Boot, Spring WebMVC, and Postgres

Maybe for very deep stacks there are optimizations whereby you only copy in deeper frames lazily under the assumption they won’t be used yet? Also, what is the story with preemption – if a virtual thread spins in an infinite loop, will it effectively hog the carrier thread or can it be descheduled? Finally, I would be really interested to see the impact on debugability. I did some related work where we were trying to get the JVM to run on top of a library operating system and a libc that contained a user level threading library. Debugging anything concurrency related became a complete nightmare since all the gdb tooling only really understood the underlying carrier threads. That’s not to say every Java library is virtual-thread-friendly.

This is a shift in mindset you have to make when you work with this new type of thread. When we created a thread in a previous version of Java, it also created a thread managed and scheduled by the operating system . These threads that the OS manages are called platform threads. To create a platform thread, you need to make a system call, and these are expensive.

virtual threads

Of course, instead of blocking the database driver, we will use its reactive alternative. The implementation is provided inside the PersonRepositoryAsyncAwait class. Reactive style programming solved the problem of platform threads waiting for responses from other systems. The asynchronous APIs do not wait for the response, rather they work through the callbacks. Whenever a thread invokes an async API, the platform thread is returned to the pool until the response comes back from the remote system or database.

Where Virtual Threads make sense

Yeah that’s what I meant, a lightweight threading mechanism provided by the OS. Yeah, scheduler activations were one approach, albeit one that wasn’t deemed effective. It kind of petered off as kernel only threads were fast enough with significantly less complexity.

virtual threads

In this article, you will learn how to integrate Quarkus with Java virtual threads. Currently, virtual threads is one the hottest topics in Java world. Virtual threads reduce the effort of writing, maintaining, and observing high-throughput concurrent applications.

Existing agents that enable the ThreadStart and ThreadEnd events may encounter performance issues since they lack the ability to limit the events to platform threads. only supports the monitoring and management of platform threads. The findDeadlockedThreads() method finds cycles of platform threads that are in deadlock; it does not find cycles of virtual threads that are in deadlock. In order to avoid this wasting of resource without modifying Netty upstream, we wrote an extension that modifies the bytecode of the class responsible for creating the thread locals at build time. Using this extension, performance of virtual threads in Quarkus for the Json Serialization test of the Techempower suite increased by nearly 80%, making it almost as good as reactive endpoints.


We have removed many uses of thread locals from the java.base module in preparation for, to reduce memory footprint when running with millions of threads. Developers sometimes use thread pools to limit concurrent access to a limited resource. For example, if a service cannot handle more than 20 concurrent requests, then performing all access to the service via tasks submitted to a pool of size 20 will ensure that. Because the high cost of platform threads has made thread pools ubiquitous, this idiom has become ubiquitous as well, but developers should not be tempted to pool virtual threads in order to limit concurrency.

However, anyone who has had to maintain code like the following knows that reactive code is many times more complex than sequential code – and absolutely no fun. So far, we have only been able to overcome this problem with reactive programming, as provided by frameworks like RxJava and Project Reactor. The first one uses the traditional blocking style, it is considered blocking due to its signature. This annotation can only be used in conjunction with endpoints annotated with @Blocking or considered blocking because of their signature. You can visit Execution model, blocking, non-blockingfor more information. See the Executors documentation for more about the executor methods.

The amount of heap space and garbage collector activity that virtual threads require is difficult, in general, to compare to that of asynchronous code. A million virtual threads require at least a million objects, but so do a million tasks sharing a pool of platform threads. In addition, application code that processes requests typically maintains data across I/O operations. Overall, the heap consumption and garbage collector activity of thread-per-request versus asynchronous code should be roughly similar.

  • The goal of structured concurrency is to totally avoid those by making sure the lifetime of child tasks is always contained within the lifetime of their parent tasks.
  • ExecutorService has been retrofitted to implement AutoCloseable, so it can be used with try-with-resources, and the close method shuts down the executor and waits for tasks to complete.
  • I find that an easier model to think about, and I opt into multithreading when I need it.
  • Thus, scheduling virtual threads is the responsibility of the JVM.

Thread.threadId() is added as a final method to return the thread’s identifier. If code in an existing source file extends Thread and the subclass declares a method named threadId with no parameters then it will not compile. We will extend the jtreg test harness to allow existing tests to be run in the context of a virtual thread. The API requires the implementation to have a reference to all live threads in the group. This adds synchronization and contention overhead to thread creation, thread start, and thread termination.

20 years ago a language whose C FFI was as cumbersome as Go’s would be laughed at. I was not saying that Java creates a new thread for every IO operation but that async/await in JavaScript etc. must do something like starting a new “pseudo-thread”. And that is why debugging in Java is easier – because it doesn’t need to start a new thread. Since glued stack traces could be in-theory separate threads you might get weird behaviors where values of objects across the stack can be wildly different. When the version number scheme changed and LTS was introduced, many companies got confused and stopped their practice of upgrading to new feature releases.

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The API defines suspend(), resume(), and stop() methods that are inherently deadlock prone and unsafe. The API defines enumerate() methods that are inherently racy. The stream decoders and encoders used by InputStreamReader and OutputStreamWriter now use the same lock as the enclosing InputStreamReader or OutputStreamWriter.

Thread.getAllStackTraces() now returns a map of all platform threads rather than all threads. Enable server applications written in the simple thread-per-request style to scale with near-optimal hardware utilization. Anyone who has ever maintained a backend application under heavy load knows that threads are often the bottleneck. For every incoming request, a thread is needed to process the request. One Java thread corresponds to one operating system thread, and those are resource-hungry.


Remember that Java has been multithreaded since its inception, and project loom java don’t change any of the threading model. I honestly doubt that older code is “goroutine”-aware, as virtual threads are used in a different way than ordinary OS threads. I don’t think there’s any code that spawned hundreds of thousands of OS threads before, which would be the main benefit of using virtual threads.


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