How to Use Java 19 Virtual Threads by omgzui Javarevisited Sep, 2022

How to Use Java 19 Virtual Threads by omgzui Javarevisited Sep, 2022

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. When used by programs, a richer relational structured concurrency between threads can be displayed. A server application like this, with simple blocking code, can scale well because it can use a large number of virtual threads. Executor.newVirtualThreadPerTaskExecutor() is not the only way to create virtual threads.

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. Nearly all blocking points in the JDK were made aware of virtual threads, and will unmount a virtual thread rather than blocking it. 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.

Set Event Reminder

Each actor supports only a specific subset of Message implementations. Ideally, we would want to add this as a constraint on ActorRef using a generic parameter. Still, this seems to be impossible due to Java’s limited generics . Instead of shared memory & locks, we can base our design on message passing. That’s the bedrock of the actor model, as implemented in Erlang and Akka, but it also underpins Go’s goroutines. When invoked on a virtual thread, Thread.getThreadGroup() returns a placeholder thread group with the name “VirtualThreads“.

Enable server applications written in a simple thread-per-request style to scale with near-optimal hardware utilization. Unlike ActorRef, you can see that the behavior is constrained to a subtype of messages that the actor handles. The actor has the option to provide the answer asynchronously if, e.g., it depends on the replies arriving from yet another actor.

Behind the scenes, the JVM created a few platform threads for the virtual threads to run on. Since we are free of system calls and context switches, we can run thousands of virtual threads on just a few platform threads. Unfortunately, writing scalable code that interacts with the network is hard.

Java 19 brings the first preview of project loom java to the Java platform; this is the main deliverable of OpenJDKs Project Loom. This is one of the biggest changes to come to Java in a long time — and at the same time, is an almost imperceptible change. There is almost zero new API surface, and virtual threads behave almost exactly like the threads we already know.

Everyone out of the pool

Notice the blazing fast performance of virtual threads that brought down the execution time from 100 seconds to 1.5 seconds with no change in the Runnable code. In this way, Executor will be able to run 100 tasks at a time and other tasks will need to wait. As we have 10,000 tasks so the total time to finish the execution will be approximately 100 seconds. But this pattern limits the throughput of the server because the number of concurrent requests becomes directly proportional to the server’s hardware performance. So, the number of available threads has to be limited even in multi-core processors. Traditionally, Java has treated the platform threads as thin wrappers around operating system threads.

The hang/resume implementation allows the debugger to hang and resume virtual threads, and allows carrier threads to be hung when a virtual thread is hung. The java.io package provides APIs for byte streams and character streams. The implementation of these APIs is highly synchronous and changes are needed to avoid fixing them when they are used in virtual threads.

Modeling Entities

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). The short answer is yes; you can use the existing executors with virtual threads by supplying them with a virtual thread factory.

• The second category, synchronous, are more interesting from the perspective of how they behave when run in a virtual thread.
• On the first line, we create a virtual thread factory that will handle the thread creation for the executor.
• Susanne Kaiser is a software consultant working with teams on microservice adoption.
• You won’t need to make these changes once virtual threads are promoted out of preview.

A parked virtual thread may be unparked, which re-enables it for scheduling. 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.

Introducing virtual threads

Servers today can handle far larger numbers of open socket connections than the number of threads they can support, which creates both opportunities and challenges. Something that other languages like Go or Erlang had for years or decades. A more serious problem with async/await is the “function color” problem, where methods are divided into two kinds — one designed for threads and another designed for async methods — and the two do not interoperate perfectly. This is a cumbersome programming model, often with significant duplication, and would require the new construct to be introduced into every layer of libraries, frameworks, and tooling in order to get a seamless result.

For example, the server application shown earlier includes the following lines of code that contain calls to the blocking operation. Schedulers do not currently implement time-sharing for virtual threads. Time-sharing is a forced preemption of threads that take up an allocated amount of CPU time. While time-sharing can be effective using a few hundred platform threads, it is unclear whether time-sharing would be as effective using a million virtual threads. A clear representation of the state of a running program is also essential for troubleshooting, maintenance, and optimization, and the JDK has long provided mechanisms for debugging, analyzing, and monitoring threads. These tools should perform the same operations on virtual threads-perhaps with some reconciliation of their extensive operations-because they are, after all, instances of java.lang.

The stack grows and shrinks as the application runs, both for memory efficiency and to accommodate stacks of arbitrary depth (up to the JVM-configured platform thread stack size). This efficiency allows for a large number of virtual threads, which in turn allows for the continuous per-request style survivability of threads in server applications. To enable applications to scale while remaining in harmony with the platform, we should strive to preserve per-request thread styles by implementing threads more efficiently so they can be richer. Operating systems cannot implement OS threads more efficiently because different languages and runtimes use the thread stack in different ways.

Meeting Virtual Threads

QCon Plus brings together the world’s most innovative senior software engineers across multiple domains to share their real-world implementation of emerging trends and practices. A new command that allows the debugger to test if a thread is a virtual thread. JNI defines a new function, IsVirtualThread, to test whether an object is a virtual thread. The remaining subsections detail the changes proposed in the Java platform and its implementation. JDK Flight Recorder events will be raised when a thread blocks while being fixed. 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.

Why would we implement yet another unit of concurrency — one that is only syntax-deep — which does not align with the threads we already have? This might be more attractive in another language, where language-runtime co-evolution was not an option, but fortunately we didnt have to make that choice. The loading and unloading of virtual threads occurs frequently and transparently, and does not block any OS threads.

Memory usage and interaction with garbage collection

In this article we’ll take a look at how the Java platform’s Networking APIs work under the hood when called on https://globalcloudteam.com/. Building up on the previous topic Structured Concurrency works perfectly with virtual threads, where virtual threads deliver an abundance of threads and structured concurrency ensures that they are correctly and robustly coordinated. Virtual threads are so lightweight that it is perfectly OK to create a virtual thread even for short-lived tasks, and counterproductive to try to reuse or recycle them. Indeed, virtual threads were designed with such short-lived tasks in mind, such as an HTTP fetch or a JDBC query.

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. Virtual threads are still threads; debuggers can step through them like platform threads. Java Flight Recorder and the jcmd tool have additional features to help you observe virtual threads in your applications. It is worth mentioning that we can create a very high number of virtual threads in an application without depending on the number of platform threads.

A platform thread runs Java code on its underlying OS thread, and the platform thread captures its OS thread for the platform thread’s entire lifetime. Consequently, the number of available platform threads is limited to the number of OS threads. With the growing demand of scalability and high throughput in the world of microservices, virtual threads will prove a milestone feature in Java history.

To be able to execute a piece of code requires an execution environment. If a program has only one executing environment, then we call this program a single-threaded program. 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(). Consequently, this example prints a message once the virtual thread’s task is complete. Platforms threads are suitable for running all types of tasks but may be a limited resource.

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While platform threads have a monopoly on valuable OS threads, virtual threads do not. The number of virtual threads can be much larger than the number of operating system threads. For application programmers, they represent an alternative to asynchronous-style coding such as using callbacks or futures. 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.