Guide of Virtual Threads Lightweight threads in Java Adam Gamboa G Developer

Virtual threads are a big change under the hood, but they are intentionally easy to apply to an existing codebase. Virtual threads will have the biggest and most immediate impact on servers like Tomcat and GlassFish. Such servers should be able to adopt virtual threading with minimal effort. Applications running on these server will net scalability gains without any changes to the code, which could have enormous implications for large-scale applications. Consider a Java application running on many servers and cores; suddenly, it will be able to handle an order-of-magnitude more concurrent requests (although, of course, it all depends on the request-handling profile).

Virtual threads introduce an abstraction layer between operating-system processes and application-level concurrency. Said differently, virtual threads can be used to schedule tasks that the Java virtual machine orchestrates, so the JVM mediates between the operating system and the program. Indeed, there was some popular call to add async/await to Java, as C# and Kotlin have. On a modest desktop system with no special configuration options, running this program takes about 1.6 seconds in a cold start, and about 1.1 seconds after warmup.

📝 ModelMapper is a powerful library in Spring Boot that simplifies the process of mapping objects from one type to another.

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. There is no way of obtaining the result of the executed Runnable, if necessary. You will have to use
a Callable for that (explained in the following sections). I will take a look at each of these methods in the following sections. You will see several more examples of how to use the ExecutorService throughout this tutorial.

java virtual threads

The other ones were “queued” are the average response time increased in time. Remember that thanks to the @ConditionalOnProperty annotation, we can switch between virtual threads and standard threads by only changing the value of the variable in the application.yaml. In this short tutorial, we’ll see how it is possible to leverage the great power of virtual threads in a Spring Boot Application.

Nested Class Summary

Such locks don’t pin the virtual thread, making the cooperative scheduling work again. Pooling is not required with virtual threads because they are cheap to create and dispose of, and therefore pooling is unnecessary. Instead, you can think of the JVM as managing the thread pool for you. Many programs do use executors, however, and so Java 19 includes a new preview method in executors to make refactoring to virtual threads easy. Littles Law doesnt care about what portion of the time is spent “doing work” vs “waiting”, or whether the unit of concurrency is a thread, a CPU, an ATM machine, or a human bank teller. It just states that to scale up the throughput, we either have to proportionally scale down the latency or scale up the number of requests we can handle concurrently.

  • So, we don’t need to allocate a gazillion of memory to fit every possible use case.
  • This could lead to the under-desirable state of an application that has maxed out its thread allocation while still having low CPU utilization.
  • Instead, use semaphores to make sure only a specified number of threads are accessing that resource.
  • With Loom we get tail-call optimizations which should reduce memory usage.
  • Kotlin’s coroutines have no direct support in the JVM, so they are supported using code generation by the compiler.
  • But, this scalability comes at a great cost — you often have to give up some of the fundamental features of the platform and ecosystem.

(The name “virtual thread” is supposed to be reminiscent of virtual memory that is mapped to actual RAM.) Virtual threads became a preview feature in Java 20 (JEP 436) and are final in Java 21. The second mariadb developers category, synchronous, are more interesting from the perspective of how they behave when run in a virtual thread. Within this category are NIO channels that can be configured in a non-blocking mode.

Maintaining Context and Debugging

The last article introduced the exciting new features of Java 19, of which the most anticipated should be virtual threads. This article will introduce you to virtual threads to try Java 19 virtual threads. Last, the method sets the runContinuation field, a Runnable object used to run the continuation. We can run the above method also with the jdk.tracePinnedThreads property set to see that no thread is pinned to its carrier thread during the execution. The JVM added a new carrier thread to the pool when it found no carrier thread. So the daniel virtual thread is scheduled on the new carrier thread, executing concurrently and interleaving the two logs.

A virtual thread is mounted on its carrier thread when it is in the states colored green in the above diagram. In states colored in light blue, the virtual thread is unmounted from its carrier thread. The way we start threads is a little different since we’re using the ExecutorService. Every call to the submit method requires a Runnable or a Callable instance. The submit returns a Future instance that we can use to join the underlying virtual thread.

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With virtual threads, you should use alternative mechanisms for controlling access to limited resources. Instead of an overall limit on concurrent tasks, protect each resource in an appropriate way. For database connections, the connection pool may already do the right thing.

java virtual threads

Historically, threads in Java have been a relatively heavy-weight object as threads were tied to the underlying thread provided by the OS. The threads are yielding control to each other, state preserved and then resumed, a true CoRoutine. The best part is that it is identical to a regular blocking code. This code works just fine, I was able to spawn more than 20 million such threads on my machine. This is to be expected since the user mode threads are nothing more than an object in memory that the JVM manages. Here we try to create 1 million regular threads, all the thread does is sleep 1 second and then die.

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Having said that virtual threads also consume similar amounts of memory (or at least that is what I understood). With Loom we get tail-call optimizations which should reduce memory usage. Also, synchronization and thread context copy should still be a problem of a similar size.

java virtual threads

The operating system only knows about platform threads, which remain the unit of scheduling. To run code in a virtual thread, the Java runtime arranges for it to run by mounting it on some platform thread, called a carrier thread. Mounting a virtual thread means temporarily copying the needed stack frames from the heap to the stack of the carrier thread, and borrowing the carriers stack while it is mounted. In other words, the platform thread does not switch
between executing multiple virtual threads – except in the case of blocking network calls. As long as a virtual
thread is running code and is not blocked waiting for a network response – the platform thread will keep
executing the same virtual thread.

Pinned Virtual Threads

To increase the throughput of the system, we have to continuously increase the number of threads, but the threads of the machine are expensive and the number of available threads is limited. To increase the performance of the application, we will add more and more Java threads. When the system schedules Java threads, it will occupy a lot of resources to handle thread context switching. A similar API Thread.ofPlatform() exists for creating platform threads as well. Virtual threads are best suited to executing code that spends most of its time blocked, waiting for data to arrive on a network socket or waiting for an element in queue for example.

So the synchronous Java networking APIs should scale comparably to that of the more complicated asynchronous and non-blocking code constructs. For this tutorial, it is essential to grasp that virtual threads are far cheaper than platform threads to operate. This is why it’s possible to create millions of virtual threads without having out-of-memory problems, rather than the few hundred we can create with standard platform (or kernel) threads. 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.

Java Virtual Threads – Project Loom

This means that the –enable-preview flag is needed to enable virtual thread support. For CPU-bound workloads, we already have tools to get to optimal CPU utilization, such as the fork-join framework and parallel streams. Java developers may recall that in the Java 1.0 days, some JVMs implemented threads using user-mode, or “green”, threads. Virtual threads bear a superficial similarity to green threads in that they are both managed by the JVM rather than the OS, but this is where the similarity ends. The green threads of the 90s still had large, monolithic stacks.

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