Developping an Asynchronous Application with Virtual Threads and Structured Concurrency

You can find the GitHub repo for this lab here: https://github.com/JosePaumard/2025_JavaOne-Loom-lab

One of the most exciting features delivered by the JDK 21 are Virtual Threads developped by the Loom project. Their promise is to enable the "simple thread-per-request style to scale with near-optimal hardware utilization". Before Virtual Threads, this could could only be achieved with reactive programming, which gives you excellent throughput, but with patternsthat are hard to write, hard to read, hard to debug, and hard to profile. It gives you excellent performance, but at the cost of maintainability. This hands-on lab takes you through the writing of a virtual thread based application, that uses structured concurrency to parallelize your requests and scoped values to pass your sensitive information without relying on method parameters. You will see the patterns of code the Loom project gives you, to achieve the same throughput as a classical reactive application. You will then be able to compare the patterns of code of both approaches, to choose which one you prefer.

Transcript

1. Developing Async Applications with Virtual Threads and Structured Concurrency The Loom Project José Paumard Java Developer Advocate Java Platform Group Billy Korando Senior Developer Advocate Java Platform Group
2. @billykorando.bsky.social billy.korando@oracle.com https://dev.java
3. @josepaumard.bsky.social https://dev.java
4. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 4 https://dev.java/
5. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 5 Tune in! Inside Java Newscast JEP Café Road To 21 series Inside.java Inside Java Podcast Sip of Java Cracking the Java coding interview
6. https://marketplace.eclipse.org/content/java-24-support-eclipse-2025-03-435
7. https://www.jetbrains.com/idea/download/
10. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 10 https://bit.ly/javaone25-loom-lab javaone25 javaturns30
11. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 11 Structure of the Lab
12. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 12 Is it new? First ideas emerged in the early 60’s First specification for Fortran 1997 Structured Concurrency
13. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 13 Because it is about launching different tasks in different threads with an imperative programming model But… you need to be able to create threads on demand to implement it Made possible with virtual threads! Why is This Problem Interesting?
14. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 14 Stuctured Concurrency Pattern try (var scope = StructuredTaskScope.open()) { var linksSubTask = scope.fork(SomeService::readLinks); var imageSubTask = scope.fork(SomeService::readImages); scope.join(); var links = linksSubTask.get(); var images = imageSubTask.get(); var report = new Report(links, images); return report; }
15. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 15 Closing ReportScope closes the other scopes A Scope can Spawn more Scopes ReportScope ImageScope LinkScope
16. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 16 You get a legacy application that is a Travel Agency web application that sells travels And that wants to display the weather forecast 3 servers: - A Flight Company server - A Weather forecast server - Your Travel Agency server Goal of the lab
17. 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 17 This is the current state of the application And it is terrible! Some refactoring needs to be done It uses the Data Oriented Programming approach Structure of the Lab: Step 0
18. Step 0: get to know the application and refactor it 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 18 The Travel Agency Application Basic Flight Company query Basic Weather forecast query Basic combination of Flight and Weather forecast
19. Step 1 and 2 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 19 The Travel Agency Application Flight Company query Get all the flights Select the cheapest one Basic Weather forecast query Basic combination of Flight and Weather forecast
20. Step 3 Step 1 and 2 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 20 The Travel Agency Application Flight Company query Get all the flights Select the cheapest one Weather forecast query Get the first Cancel the others Basic combination of Flight and Weather forecast
21. Step 4 and 5 Step 3 Step 1 and 2 3/21/2025 Copyright © 2025, Oracle and/or its affiliates 21 The Travel Agency Application Travel Agency application Get the cheapest flight Check if the weather forecast is there If not, cancel it Weather forecast query Get the first Cancel the others Flight Company query Get all the flights Select the cheapest one