Intro to virtual threads: A new approach to Java concurrency

Virtual threads help in achieving the same high scalability and throughput as the asynchronous APIs with the same hardware configuration, without adding the syntax complexity. Also, we have to adopt a new programming style away from typical loops and conditional statements. The new lambda-style syntax makes it hard to understand the existing code and write programs because we must now break our program into multiple smaller units that can be run independently and asynchronously. The most basic way to use a virtual thread is with Thread.startVirtualThread. This is a replacement for instantiating a thread and calling thread.start().

  • Since visualizing and analyzing a large number of threads can benefit from the tool, jcmd can issue new thread dumps in JSON format in addition to plain text as follows.
  • However, they aren’t intended for long-running CPU-intensive operations.
  • supports monitoring and management of platform threads only.
  • Virtual threads are not faster threads; they do not run code any faster than platform threads.
  • 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.
  • Restricts the number of threads that can access a physical or logical resource.

Server applications typically handle concurrent user requests independently of each other, so it makes sense for applications to process requests by dedicating threads to that request for the entire duration of the request. This thread-per-request style is easy to understand, easy to program, and easy to debug and analyze because it uses the concurrency units of the platform to represent the concurrency units of the application. Launching 9000 platform threads didn’t really show much difference, the run time was the same, but one million threads test took eleven seconds which is more than double the time compared to virtual threads. The synchronous networking Java APIs, when run in a virtual thread, switch the underlying native socket into non-blocking mode. When the underlying I/O operation is ready , the virtual thread is unparked and the underlying socket operation is retried.

Enable existing code that uses the java.lang.Thread API to adopt virtual threads with minimal changes. Enable server applications written in a simple thread-per-request style to scale with near-optimal hardware utilization. Structured concurrency is all about simplifying multithreaded code that is complex to write, read and maintain by grouping multiple tasks running in different threads as a single unit of work. Simply put the idea is to bring the simplicity of single-threaded code to the multi-threaded workflows when possible. In this article we’ll take a look at how the Java platform’s Networking APIs work under the hood when called on virtual threads. In this example we use the Executors.newVirtualThreadPerTaskExecutor() to create a executorService.

However, the Java runtime can implement Java threads in a way that separates the one-to-one correspondence between Java threads and OS threads. 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 Thread Model and Virtual Threads

One of the compelling value propositions of Project Loom is to avoid having to make this choice – it should be possible for the synchronous code to scale. With Threads being cheap to create, project Loom also brings structured concurrency to Java. With structured concurrency, you bind the lifetime of a thread to a code block. Inside your code block, you create the threads you need and leave the block when all the threads are finished or stopped. On the first line, we create a virtual thread factory that will handle the thread creation for the executor. Next, we call the new method for each executor and supply it the factory that we just created.

virtual threads

Upon us receiving your reply, you’ll be activated in the group for 30 days and be sent some basic information. The chapter’s Membership Committee will personally follow up with you to help you settle in. At the conclusion of the 30-day trial, it’s hoped that you’ll join EAC Virtual Threads; if you decide it’s not for you, then you’ll be removed from EAC-VT. ShowingAll Productsvrchat vrchat asset vrchat clothing vrc virtualthreads Load more… Let us understand the difference between both kinds of threads when they are submitted with the same executable code. Virtual threads do not have permissions when run with the SecurityManager set.

With virtual threads, the application instantiates virtual threads and thus expresses the need for concurrency. But it is the JVM that obtains and releases the resources from the operating system. They don’t need the additional overhead or the functionality of thread pools. Because virtual threads are inexpensive and plentiful, many programming techniques you would usually use because platform threads are expensive and heavyweight are no longer applicable or recommended. EchoClient creates a socket, thereby getting a connection to EchoServer. It reads input from the user on the standard input stream, and then forwards that text to EchoServer by writing the text to the socket.

Running Spring Applications on Virtual Threads

Locking and I/O operations are scheduling points where a carrier thread is re-scheduled from one virtual thread to another. A parked virtual thread may be unparked, which re-enables it for scheduling. 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. Similarly, virtual threads are cheap and plentiful, and share the scarce and expensive platform threads as needed, and inactive virtual thread stacks are “paged” out to the heap.

The project is still in preview, and the APIs can change before we see it in production. But it’s nice to explore the new APIs and see what performance improvements it already gives us. Note that the following syntax is part of structured concurrency, another new feature proposed in Project Loom. Thread groups are now eligible for garbage collection when there are no active threads in the thread group and no other any other threads keep the thread group active. A new method com.sun.jdi.ThreadReference to test if a thread is virtual.

The getURL method is trivially written to use the synchronous URLConnection API to get the response. The retrieveURLs method downloads and returns the response of a number of given URLs. Before proceeding further, we need to know a little about the new kind of threads in Project Loom – Virtual Threads. You can take part in all of these – all from the comfort of home, just as long as you have on-line access via computer or web-enabled mobile device.

Virtual Threads is a preview API, disabled by default

I’ve also made a few changes to enable virtual threads in the Java 19 preview. You won’t need to make these changes once virtual threads are promoted out of preview. Using conventional Java threads, when a server was idling on a request, an operating system thread was also idling, which severely limited the scalability of servers.

virtual threads

Executor.newVirtualThreadPerTaskExecutor() is not the only way to create virtual threads. The new java.lang.Thread.BuilderAPI, discussed below, can create and start virtual threads. Conversely, the situation is not much better if the program uses an ExecutorService that gets its platform threads from a pool, such as Executor.newFixedThreadPool. 200 platform threads will be created by the ExecutorService to be shared by all 10,000 tasks, so many tasks will run sequentially instead of concurrently, and the program will need to run sequentially.

More about executor methods

A full stack engineer, with some medicinal knowledge, likes to read and share. It is worth noting that Thread.ofVirtual().start is equivalent to Thread.startVirtualThread. To demo it, we have a very simple task that waits for 1 second before printing a message in the console.

With Java 19, VS Code Now Does Virtual Threads While Debugging – Visual Studio Magazine

With Java 19, VS Code Now Does Virtual Threads While Debugging.

Posted: Mon, 24 Oct 2022 07:00:00 GMT [source]

Exceptions thrown in the virtual thread will not include the carrier’s stack frame. Thread dumps will not display the carrier’s stack frame on the virtual thread’s stack, and vice versa. Easily troubleshoot, debug, and analyze using existing JDK tools. Well, as in any other benchmark it’s impossible to tell without having something to baseline of. So lets do the same processing using platform threads and see the comparison.

Using asynchronous styles to improve scalability

Using an executor that pools threads in combination with virtual threads probably works, but it kind of misses the point of virtual 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. Virtual threads are a big change under the hood, but they are intentionally easy to apply to an existing codebase.

ReactiveX is the right approach for concurrent scenarios in which declarative concurrency (such as scatter-gather) matters. The underlying Reactive Streams specification defines a protocol for demand, back pressure, and cancellation of data pipelines without limiting itself to non-blocking API or specific Thread usage. For this demonstration, I’ve created a simple Java application with the Maven archetype.

The parallelism of the scheduler is the number of platform threads available for scheduling virtual threads. By default, it is equal to the available processors, but it can be adjusted using the system property jdk.virtualThreadScheduler.parallelism. Note that this ForkJoinPool is different from the public pool, for example, it is used for parallel stream implementations and works in LIFO mode. In the simplest terms a virtual thread is not directly tied to a particular OS thread while a platform thread is a thin wrapper around an OS thread. Project Loom is intending to deliver Java VM features and APIs to support easy-to-use, high-throughput lightweight concurrency and new programming models on the Java platform. This brings many interesting and exciting prospects, one of which is to simplify code that interacts with the network.

Instead of running concurrently, the program will take a long time to complete. For this program, a pool with 200 platform threads would only achieve a throughput of 200 tasks per second, while the virtual threads would have a throughput of about 10,000 tasks per second (after a full warm-up). Thread dumps are another popular tool for troubleshooting applications written in a thread-per-request style. Unfortunately, the JDK’s legacy thread dumps, obtained using jstack or jcmd, provide a flat list of threads. This is suitable for tens or hundreds of platform threads, but not for thousands or millions of virtual threads. Therefore, instead of extending the traditional thread dump to include virtual threads, we will introduce a new thread dump in jcmd to present virtual threads along with platform threads, all of which are grouped in a meaningful way.

Platform threads

Unlike the platform thread stack, the virtual thread stack is not the GC root, so the references contained in it are not traversed by the garbage collector performing concurrent scans in a stop-world pause. Of course, if the virtual thread is running, or if it is blocked and may be unblocked, it will not be garbage collected. Virtual threads are not faster threads-they do not run code faster than platform threads. They may be much more numerous than platform threads, so by Little’s law they achieve the higher concurrency required for higher throughput.

All told, we could see virtual threads as a pendulum swing back towards a synchronous programming paradigm in Java, when dealing with concurrency. This is roughly analogous in programming style to JavaScript’s introduction of async/await. In short, writing correct asynchronous behavior with simple synchronous syntax becomes quite easy—at least in applications where threads spend a lot of time idling. 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.

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