Records can be used in any other scenario, like creating POJOs (plain old Java objects). This code example will print out the object returned by one of the Callable’s in the
given collection. Once the thread has delegated the java project loom task to the ExecutorService, the thread continues its own execution
independent of the execution of that task. The ExecutorService then executes the task concurrently,
independently of the thread that submitted the task.

  • Java developers may recall that in the Java 1.0 days, some JVMs implemented threads using user-mode, or “green”, threads.
  • JVM then copies the context of Virtual thread on to Platform thread.
  • Records can be used in any other scenario, like creating POJOs (plain old Java objects).
  • It’s available since Java 19 in September 2022 as a preview feature.
  • Creating a virtual thread is very cheap, both in space and time.
  • The invokeAny() method takes a collection of Callable objects, or subinterfaces
    of Callable.

The constructs used are out of the scope of this article and I will write a separate article covering the internal constructs used. We can also use the ExecutorService, which manages the scheduling and execution of threads. Below example illustrates the process of launching virtual threads using the executor service. So, applications create a pool of threads, that are managed by an executor. A free thread picks up the task from the queue and executes it.

Working with Virtual Threads in Spring 6

If you need to submit a task to a Java ExecutorService and you need a result from the task,
then you need to make your task implement the Callable interface. Otherwise your task can
just implement the Runnable interface. If one of the tasks complete (or throws an exception), the rest of the Callable’s are cancelled. The submit() method returns a Java Future object which can be used to
check when the Runnable has completed.

In concurrent programming, we should write programs as if they were sequential. In fact, the more straightforward way to write concurrent programs in Java is to create a new thread for every concurrent task. For CPU-bound workloads, we already have tools to get to optimal CPU utilization, such as the fork-join framework and parallel streams. To locate uses of thread locals in your app, run with the VM flag jdk.traceVirtualThreadLocals.

Advantages of Virtual Threads

This is explained in more detail in later sections of this
Java virtual thread tutorial. Now we will create 10,000 threads from this Runnable and execute them with virtual threads and platform threads to compare the performance of both. We will use the Duration.between() api to measure the elapsed time in executing all the tasks. 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.

java 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. For each created virtual thread, the JVM schedules its execution on a platform thread, temporarily copying the stack chunk for the virtual thread from the heap to the stack of the platform thread. We said that the platform thread becomes the carrier thread of the virtual thread. As we said, both projects are still evolving, so the final version of the features might differ from what we will see here. Future articles to come will focus on structured concurrency and other cool features of Project Loom.

Virtual Threads

These virtual threads are managed by JVM, so they do not add extra context-switching overhead as well because they are stored in RAM as normal Java objects. Apart from the number of threads, latency is also a big concern. If you watch closely, in today’s world of microservices, a request is served by fetching/updating data on multiple systems and servers. While the application waits for the information from other servers, the current platform thread remains in an idle state. This is a waste of computing resources and a major hurdle in achieving a high throughput application. As we said at the beginning of this article, with virtual threads, it’s not the case anymore.

java virtual threads

They offer exceptional benefits, making them ideal for high-throughput concurrent applications. Note that in Java 21 [JEP-444], virtual threads now support thread-local variables all of the time. It is no longer possible, as it was in the preview releases, to create virtual threads that cannot have thread-local variables. 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. For example, we can have only a few database connections or network connections to other servers. It is worth mentioning that we can create a very high number of virtual threads (millions) in an application without depending on the number of platform threads.

Kafka Streams?—?How to build an advanced stateful data stream processing

While virtual threads present a dramatic change to how the JVM works, the code is actually very similar to conventional Java threads. The similarity is by design and makes refactoring existing applications and servers relatively easy. This compatibility also means that existing tools for monitoring and observing threads in the JVM will work with virtual threads. In this architecture, the application instantiates virtual threads and the JVM assigns the compute resources to handle them. Contrast this to conventional threads, which are mapped directly onto operating system (OS) processes.

What’s New Java 21? – iProgrammer

What’s New Java 21?.

Posted: Tue, 17 Oct 2023 17:54:39 GMT [source]

With regular threads, it is difficult to reach high levels of concurrency with blocking calls due to context switch overhead. Requests can be issued asynchronously in some cases (e.g. NIO + Epoll or Netty io_uring binding), but then you need to deal with callbacks and callback hell. Virtual threads are wrapped upon platform threads, so you may consider them an illusion that JVM provides, the whole idea is to make lifecycle of threads to CPU bound operations. Having said that virtual threads also consume similar amounts of memory (or at least that is what I understood).

Virtual Threads Look Promising

Although, there are multiple advantages of using Virtual threads, they can’t be used if you are running CPU bound tasks. Moreover, there is an additional overhead for JVM to manage the virtual thread. Virtual threads address the challenges and limitations of Thread per request model and Asynchronous programming. The below diagram illustrates the process of how Virtual threads are executed on the underlying platform threads. And we were able to develop applications with fixed number of threads. As seen in the previous section, there is an upper limit on the number of threads that a Java application can create.

java virtual threads

In this example, we ran our continuation and, at some point, decided to stop the processing. Then once we re-ran it, our continuation continued from where it left off. By the output, we see that the run() method was called twice, but the continuation was started once and then continued its execution on the second run from where it left off.

Isnt this just “green threads”?

Virtual threads are short-lived, perform specific tasks, and are plentiful. Platform threads are heavyweight, long-lived, and may need pooling. Using virtual threads maintains the thread-per-request style while optimizing hardware utilization. Now let’s consider the two main ways you’ll actually use virtual threads in your code.

java virtual threads

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