Java 21: Virtual Threads

Java 21 introduces lightweight concurrency with Virtual Threads.

Virtual threads are a different approach to asynchronous programming. Instead of having to rewrite everything using async/await keywords. Java will take care of everything.

Discover the changes introduced with JDK 21 and learn how Virtual Threads behaves with code examples demonstrating I/O Bound Tasks, CPU Bound Tasks, and Cooperative CPU Bound Tasks. Learn how the synchronized keyword and locks work in the context of Virtual Threads.

https://youtu.be/JWZxyrHBppA

Transcript

1. JDK 21
   LTS
   Virtual
   Threads
   a Different Approach to
   Async/Await
   

   View Slide

2. Aims to Bring
   easy-to-use, high-throughput,
   lightweight concurrency
   and new programming models
   on the Java platform.
   JDK 21
   LTS
   

   View Slide

3. JDK 21: Virtual Threads
   A different Approach to asynchronous programming
   C#, Python, Javascript, C++, Rust
   async/await
   Introduced New Keywords
   requiring a significant rewrite
   to take advantage of this model
   choose
   code compatibility
   minimizing the impact on existing code
   to benefit from this model
   

   View Slide

4. JDK 21: Threads
   Platform Threads
   Kernel space
   User space (JVM)
   Platform Threads
   Typically mapped 1:1 to kernel threads
   scheduled by the operating system.
   // create a platform thread, and use .start() to start it.
   Thread thread = new Thread(Runnable, "thread-name")
   thread.start();
   // create a platform thread, and use .start() to start it.
   Thread thread = Thread.ofPlatform().name("thread-name").unstarted(Runnable);
   thread.start();
   // create a platform thread and start it. No need to call .start()
   Thread thread = Thread.ofPlatform().name("thread-name").start(Runnable);
   

   View Slide

5. JDK 21: Threads
   Kernel space
   User space (JVM)
   Platform Threads
   Typically mapped 1:1 to kernel threads
   scheduled by the operating system.
   Platform Threads are not cheap
   - startup time: ~1ms
   - memory consumption: 2MB of stack
   - context switch: ~100μs
   Platform Threads & Executor Services
   

   View Slide

6. JDK 21: Threads
   Kernel space
   User space (JVM)
   Platform Threads
   Typically mapped 1:1 to kernel threads
   scheduled by the operating system.
   Platform Threads are not cheap
   - startup time: ~1ms
   - memory consumption: 2MB of stack
   - context switch: ~100μs
   try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
   for (int i = 0; i < 100; ++i) {
   executor.submit(() -> myTask());
   }
   }
   Platform Threads & Executor Services
   

   View Slide

7. JDK 21: Threads
   Kernel space
   User space (JVM)
   Platform Threads
   Typically mapped 1:1 to kernel threads
   scheduled by the operating system.
   Platform Threads are not cheap
   - startup time: ~1ms
   - memory consumption: 2MB of stack
   - context switch: ~100μs
   Task Queue
   Platform Threads & Executor Services
   try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
   for (int i = 0; i < 100; ++i) {
   executor.submit(() -> myTask());
   }
   }
   

   View Slide

8. JDK 21: Threads
   Kernel space
   User space (JVM)
   Platform Threads
   Typically mapped 1:1 to kernel threads
   scheduled by the operating system.
   Platform Threads are not cheap
   - startup time: ~1ms
   - memory consumption: 2MB of stack
   - context switch: ~100μs
   Task Queue
   Platform Threads & Executor Services
   try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
   for (int i = 0; i < 100; ++i) {
   executor.submit(() -> myTask());
   }
   }
   

   View Slide

9. JDK 21: Threads
   Kernel space
   User space (JVM)
   Platform Threads
   Typically mapped 1:1 to kernel threads
   scheduled by the operating system.
   Platform Threads are not cheap
   - startup time: ~1ms
   - memory consumption: 2MB of stack
   - context switch: ~100μs
   Task Queue
   Platform Threads & Executor Services
   try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
   for (int i = 0; i < 100; ++i) {
   executor.submit(() -> myTask());
   }
   }
   

   View Slide

10. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

11. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

12. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

13. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

14. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

15. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

16. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

17. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

18. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

19. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

20. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

21. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

22. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

23. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

24. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

25. JDK 21: Threads
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    Platform Threads & Executor Services
    try (ExecutorService executor = Executors.newFixedThreadPool(4)) {
    for (int i = 0; i < 100; ++i) {
    executor.submit(() -> myTask());
    }
    }
    

    View Slide

26. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    

    View Slide

27. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    

    View Slide

28. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    

    View Slide

29. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    

    View Slide

30. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Kernel space
    User space (JVM)
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    Task Queue
    

    View Slide

31. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    In most backend services
    Slow Tasks
    are I/O Bound Tasks
    

    View Slide

32. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    

    View Slide

33. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    My Task
    Not being blocked
    

    View Slide

34. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    All the threads created by .sendAsync()
    Waiting for I/O
    My Task
    Not being blocked
    

    View Slide

35. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    All the threads created by .sendAsync()
    Waiting for I/O
    My Task
    Not being blocked
    

    View Slide

36. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    All the threads created by .sendAsync()
    Waiting for I/O
    My Task
    Not being blocked
    

    View Slide

37. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    All the threads created by .sendAsync()
    Waiting for I/O
    My Task
    Not being blocked
    

    View Slide

38. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    All the threads created by .sendAsync()
    Waiting for I/O
    My Task
    Not being blocked
    

    View Slide

39. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    All the threads created by .sendAsync()
    Waiting for I/O
    My Task
    Not being blocked
    

    View Slide

40. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    All the threads created by .sendAsync()
    Waiting for I/O
    My Task
    Not being blocked
    

    View Slide

41. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    All the threads created by .sendAsync()
    Waiting for I/O
    My Task
    Not being blocked
    

    View Slide

42. JDK 21: Executor Services
    Slow Tasks & Completable Future
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Platform Threads are not cheap
    - startup time: ~1ms
    - memory consumption: 2MB of stack
    - context switch: ~100μs
    System.out.println("Active Threads " + Thread.activeCount());
    for (int i = 0; i < 128; ++i) {
    httpClient.sendAsync(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    System.out.println("Active Threads " + Thread.activeCount());
    }
    CompletableFuture and the Async feeling
    All the threads created by .sendAsync()
    Waiting for I/O
    My Task
    Not being blocked
    

    View Slide

43. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    User space (JVM)
    // create a virtual thread and start it.
    Thread thread = Thread.startVirtualThread(Runnable);
    // create a virtual thread and start it.
    Thread thread = Thread.ofVirtual().name(“thread-name").start(Runnable);
    // create a virtual thread, and use .start() to start it.
    Thread thread = Thread.ofVirtual().name("thread-name").unstarted(Runnable);
    thread.start();
    Virtual
    Threads
    JVM
    

    View Slide

44. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    Eliminates the overhead
    of
    I/O Bound Tasks
    

    View Slide

45. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    User space (JVM)
    Virtual
    Threads
    JVM
    

    View Slide

46. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    User space (JVM)
    Virtual
    Threads
    JVM
    Use them for I/O Bound Tasks
    

    View Slide

47. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    User space (JVM)
    Virtual
    Threads
    JVM
    Use them for I/O Bound Tasks
    Spends most of the time
    using CPU
    Spends most of the time
    waiting for I/O
    Longer CPU bursts Shorter CPU bursts
    CPU Bound I/O Bound
    

    View Slide

48. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    User space (JVM)
    Virtual
    Threads
    JVM
    Almost no changes to the code required!
    Java did all of the work underneath
    Rewriting the I/O & Blocking Operations
    To Cooperate with the Virtual Threads Scheduler
    

    View Slide

49. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    User space (JVM)
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    executor.submit(() -> myTask());
    }
    Virtual
    Threads
    JVM
    

    View Slide

50. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    User space (JVM)
    // create a virtual thread and start it.
    Thread thread = Thread.startVirtualThread(Runnable);
    // create a virtual thread and start it.
    Thread thread = Thread.ofVirtual().name(“thread-name").start(Runnable);
    // create a virtual thread, and use .start() to start it.
    Thread thread = Thread.ofVirtual().name("thread-name").unstarted(Runnable);
    thread.start();
    Virtual
    Threads
    JVM
    

    View Slide

51. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    // create a platform thread and start it. No need to call .start()
    Thread thread = Thread.ofPlatform().name(“my-thread-name”).start(Runnable);
    // create a virtual thread and start it.
    Thread thread = Thread.ofVirtual().name(“my-thread-name”).start(Runnable);
    boolean isVirtual = thread.isVirtual();
    

    View Slide

52. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    // create a platform thread and start it. No need to call .start()
    Thread thread = Thread.ofPlatform().name(“my-thread-name”).start(Runnable);
    // create a virtual thread and start it.
    Thread thread = Thread.ofVirtual().name(“my-thread-name”).start(Runnable);
    boolean isVirtual = thread.isVirtual();
    Thread[#29,my-thread-name,5,main]
    VirtualThread[#30,my-thread-name]/runnable@ForkJoinPool-1-worker-1
    jstack or Thread.currentThread() shows
    

    View Slide

53. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    JDK 21: Threads
    Virtual Threads
    // create a platform thread and start it. No need to call .start()
    Thread thread = Thread.ofPlatform().name(“my-thread-name”).start(Runnable);
    // create a virtual thread and start it.
    Thread thread = Thread.ofVirtual().name(“my-thread-name”).start(Runnable);
    boolean isVirtual = thread.isVirtual();
    Thread[#29,my-thread-name,5,main]
    VirtualThread[#30,my-thread-name]/runnable@ForkJoinPool-1-worker-1
    jstack or Thread.currentThread() shows
    

    View Slide

54. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Kernel space
    User space (JVM)
    Virtual
    Threads
    Carrier
    Threads
    

    View Slide

55. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Kernel space
    User space (JVM)
    Virtual
    Threads
    Carrier
    Threads
    ForkJoinPool with FIFO order
    

    View Slide

56. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Kernel space
    User space (JVM)
    Virtual
    Threads
    Carrier
    Threads
    ForkJoinPool with FIFO order
    -Djdk.virtualThreadScheduler.parallelism=16
    -Djdk.virtualThreadScheduler.maxPoolSize=256
    The number of platform threads available for scheduling virtual threads.
    It defaults to the number of available processors.
    The maximum number of platform threads available to the scheduler.
    It defaults to 256.
    

    View Slide

57. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    

    View Slide

58. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    

    View Slide

59. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    

    View Slide

60. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    

    View Slide

61. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    

    View Slide

62. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    

    View Slide

63. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    

    View Slide

64. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    

    View Slide

65. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

66. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

67. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

68. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

69. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

70. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

71. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

72. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

73. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

74. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

75. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

76. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

77. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

78. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

79. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

80. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

81. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

82. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    Task
    State
    

    View Slide

83. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    

    View Slide

84. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    Virtual
    Threads
    Carrier
    Thread
    // some cpu bound code
    long result = 0;
    for (int i = 0; i < 100; ++i) {
    result += i * 3;
    }
    // some blocking (I/O bound) code
    HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create(“https://myservice/test”))
    .GET()
    .build(), BodyHandlers.discarding());
    // more cpu bound code
    if (resp.statusCode() != 200) {
    ...
    Waiting
    Tasks
    JVM Heap
    

    View Slide

85. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    public void myTask() {
    // each execution step may run on a different Carrier Thraed
    cpuBoundOperations(); // run on CarrierThread-5
    ioBoundOperations(); // goes to "waiting"
    cpuBoundOperations(); // run on CarrierThread-3
    ioBoundOperations(); // goes to "waiting"
    cpuBoundOperations(); // run on CarrierThread-3
    // ...
    }
    

    View Slide

86. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    public void myTask() {
    // each execution step may run on a different Carrier Thraed
    cpuBoundOperations(); // run on CarrierThread-5
    ioBoundOperations(); // goes to "waiting"
    cpuBoundOperations(); // run on CarrierThread-3
    ioBoundOperations(); // goes to "waiting"
    cpuBoundOperations(); // run on CarrierThread-3
    // ...
    }
    ThreadLocals are available for compatibility
    but not really useful. Do not pool VirtualThreads!
    

    View Slide

87. Virtual Threads
    User-mode threads
    scheduled by the Java Runtime
    rather than the operating system
    Platform Threads
    Typically mapped 1:1 to kernel threads
    scheduled by the operating system.
    Carrier Threads
    Set of Platform threads responsible for
    running virtual threads.
    JDK 21: Threads
    Platform, Virtual & Carrier Threads
    public void myTask() {
    // each execution step may run on a different Carrier Thraed
    cpuBoundOperations(); // run on CarrierThread-5
    ioBoundOperations(); // goes to "waiting"
    cpuBoundOperations(); // run on CarrierThread-3
    ioBoundOperations(); // goes to "waiting"
    cpuBoundOperations(); // run on CarrierThread-3
    // ...
    }
    ThreadLocals are available for compatibility
    but not really useful. Do not pool VirtualThreads!
    ScopedValue SHARED_OBJECT = ScopedValue.newInstance();
    ScopedValues, the better alternative to ThreadLocal
    are only available as preview (in JDK 21)
    

    View Slide

88. Code Examples
    Let's see how Virtual Threads behaves
    

    View Slide

89. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    

    View Slide

90. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    We are using the synchronous .send()
    No callbacks, futures & co
    

    View Slide

91. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    // Run with -Djdk.virtualThreadScheduler.parallelism=1
    final long startTime = System.nanoTime();
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10; ++i) {
    final int taskId = i;
    executor.submit(() -> {
    ioBoundTask();
    long elapsedNs = System.nanoTime() - startTime;
    });
    }
    }
    

    View Slide

92. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    // Run with -Djdk.virtualThreadScheduler.parallelism=1
    final long startTime = System.nanoTime();
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10; ++i) {
    final int taskId = i;
    executor.submit(() -> {
    ioBoundTask();
    long elapsedNs = System.nanoTime() - startTime;
    });
    }
    }
    Carrier
    Thread
    Waiting
    Tasks
    

    View Slide

93. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    // Run with -Djdk.virtualThreadScheduler.parallelism=1
    final long startTime = System.nanoTime();
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10; ++i) {
    final int taskId = i;
    executor.submit(() -> {
    ioBoundTask();
    long elapsedNs = System.nanoTime() - startTime;
    });
    }
    }
    Carrier
    Thread
    Waiting
    Tasks
    

    View Slide

94. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    // Run with -Djdk.virtualThreadScheduler.parallelism=1
    final long startTime = System.nanoTime();
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10; ++i) {
    final int taskId = i;
    executor.submit(() -> {
    ioBoundTask();
    long elapsedNs = System.nanoTime() - startTime;
    });
    }
    }
    Carrier
    Thread
    Waiting
    Tasks
    

    View Slide

95. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    // Run with -Djdk.virtualThreadScheduler.parallelism=1
    final long startTime = System.nanoTime();
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10; ++i) {
    final int taskId = i;
    executor.submit(() -> {
    ioBoundTask();
    long elapsedNs = System.nanoTime() - startTime;
    });
    }
    }
    Carrier
    Thread
    Waiting
    Tasks
    

    View Slide

96. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    // Run with -Djdk.virtualThreadScheduler.parallelism=1
    final long startTime = System.nanoTime();
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10; ++i) {
    final int taskId = i;
    executor.submit(() -> {
    ioBoundTask();
    long elapsedNs = System.nanoTime() - startTime;
    });
    }
    }
    Carrier
    Thread
    Waiting
    Tasks
    

    View Slide

97. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    // Run with -Djdk.virtualThreadScheduler.parallelism=1
    final long startTime = System.nanoTime();
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10; ++i) {
    final int taskId = i;
    executor.submit(() -> {
    ioBoundTask();
    long elapsedNs = System.nanoTime() - startTime;
    });
    }
    }
    Carrier
    Thread
    Waiting
    Tasks
    

    View Slide

98. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    // Run with -Djdk.virtualThreadScheduler.parallelism=1
    final long startTime = System.nanoTime();
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10; ++i) {
    final int taskId = i;
    executor.submit(() -> {
    ioBoundTask();
    long elapsedNs = System.nanoTime() - startTime;
    });
    }
    }
    Carrier
    Thread
    Waiting
    Tasks
    

    View Slide

99. JDK 21: Virtual Threads
    I/O Bound Tasks
    private static long ioBoundTask() {
    try {
    // calls a service that waits 5sec before responding…
    final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
    .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
    .GET()
    .build(), BodyHandlers.discarding());
    // ...
    return resp.statusCode();
    } catch (final Exception e) {
    // ignore...
    System.err.println("http req failed: " + e.getMessage());
    return -1;
    }
    }
    // Run with -Djdk.virtualThreadScheduler.parallelism=1
    final long startTime = System.nanoTime();
    try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
    for (int i = 0; i < 10; ++i) {
    final int taskId = i;
    executor.submit(() -> {
    ioBoundTask();
    long elapsedNs = System.nanoTime() - startTime;
    });
    }
    }
    Carrier
    Thread
    Waiting
    Tasks
    

    View Slide

100. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

101. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

102. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

103. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

104. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

105. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

106. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

107. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

108. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

109. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

110. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

111. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

112. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

113. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

114. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

115. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

116. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

117. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

118. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

119. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

120. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

121. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

122. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

123. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

124. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

125. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

126. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

127. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

128. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

129. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

130. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

131. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

132. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

133. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

134. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

135. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

136. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

137. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static long ioBoundTask() {
     try {
     // calls a service that waits 5sec before responding…
     final HttpResponse resp = httpClient.send(HttpRequest.newBuilder()
     .uri(URI.create("https://hub.dummyapis.com/delay?seconds=5"))
     .GET()
     .build(), BodyHandlers.discarding());
     // ...
     return resp.statusCode();
     } catch (final Exception e) {
     // ignore...
     System.err.println("http req failed: " + e.getMessage());
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     

     View Slide

138. JDK 21: Virtual Threads
     I/O Bound Tasks
     private static int sleepBoundTask() {
     try {
     // sleep() acts as an I/O operation, allowing the task unmount
     Thread.sleep(5_000);
     return 0;
     } catch (final InterruptedException e) {
     // ignore...
     return -1;
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     final Thread[] threads = new Thread[10];
     for (int i = 0; i < threads.length; ++i) {
     final int taskId = i;
     threads[i] = Thread.ofVirtual().start(() -> {
     sleepBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     for (final Thread thread : threads) {
     thread.join();
     final boolean isVirtual = thread.isVirtual();
     }
     

     View Slide

139. JDK 21: Virtual Threads
     CPU Bound Tasks
     Virtual Threads are made for I/O Bound Tasks
     Let’s see how they will behave with CPU Bound Tasks
     

     View Slide

140. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     There are no blocking points in the code
     To Unmount the Virtual Thread
     

     View Slide

141. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     

     View Slide

142. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     

     View Slide

143. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     

     View Slide

144. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     

     View Slide

145. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     2. Completed in 5s
     

     View Slide

146. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     2. Completed in 5s
     

     View Slide

147. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     2. Completed in 5s
     3. Completed in 10s
     4. Completed in 10s
     

     View Slide

148. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     2. Completed in 5s
     3. Completed in 10s
     4. Completed in 10s
     

     View Slide

149. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     2. Completed in 5s
     3. Completed in 10s
     4. Completed in 10s
     5. Completed in 15s
     6. Completed in 15s
     

     View Slide

150. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     2. Completed in 5s
     3. Completed in 10s
     4. Completed in 10s
     5. Completed in 15s
     6. Completed in 15s
     

     View Slide

151. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     2. Completed in 5s
     3. Completed in 10s
     4. Completed in 10s
     5. Completed in 15s
     6. Completed in 15s
     7. Completed in 20s
     8. Completed in 20s
     

     View Slide

152. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     2. Completed in 5s
     3. Completed in 10s
     4. Completed in 10s
     5. Completed in 15s
     6. Completed in 15s
     7. Completed in 20s
     8. Completed in 20s
     

     View Slide

153. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Threads
     1. Completed in 5s
     2. Completed in 5s
     3. Completed in 10s
     4. Completed in 10s
     5. Completed in 15s
     6. Completed in 15s
     7. Completed in 20s
     8. Completed in 20s
     9. Completed in 25s
     10.Completed in 25s
     

     View Slide

154. JDK 21: Virtual Threads
     CPU Bound Tasks
     private static long cpuBoundTask() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     count++;
     }
     return count;
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=2
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     For CPU bound Tasks
     Virtual Threads gives no advantage
     over traditional
     (Platform Thread based)
     ExecutorServices
     And I/O Bound Tasks
     Have to wait
     CPU Bound Tasks to Finish
     

     View Slide

155. Virtual
     Threads
     Carrier
     Threads
     CPU Bound
     Tasks
     Platform
     Threads
     Send CPU and I/O bound tasks to dedicated executors
     ThreadPoolExecutor VirtualThraedPerTaskExecutor
     JDK 21: Virtual Threads
     

     View Slide

156. JDK 21: Virtual Threads
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     CPU Bound Tasks
     can cooperate
     Using the yield() method
     

     View Slide

157. JDK 21: Virtual Threads
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     Carrier
     Thread
     Waiting
     Tasks
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

158. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

159. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

160. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

161. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

162. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

163. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

164. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

165. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

166. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

167. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

168. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

169. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

170. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

171. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

172. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

173. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

174. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

175. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

176. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

177. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

178. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

179. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

180. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

181. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

182. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

183. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

184. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

185. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

186. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

187. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

188. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

189. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

190. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

191. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

192. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

193. JDK 21: Virtual Threads
     Carrier
     Thread
     Waiting
     Tasks
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     

     View Slide

194. JDK 21: Virtual Threads
     Cooperative CPU Bound Tasks
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     cpuBoundTaskWithYield();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     private static long cpuBoundTaskWithYield() {
     final long startTime = System.nanoTime();
     long count = 0;
     while ((System.nanoTime() - startTime) < TimeUnit.SECONDS.toNanos(5)) {
     if (count++ % 100 == 0) {
     Thread.yield();
     }
     }
     return count;
     }
     Slower than running the task alone
     (Since the CPU is shared)
     But it’s the same behaviour
     of running multiple platform Threads
     

     View Slide

195. JDK 21: Virtual Threads
     The synchronized keyword
     private final static Object[] lock = new Object[4];
     static {
     for (int i = 0; i < lock.length; ++i) {
     lock[i] = new Object();
     }
     }
     private static long ioSynchronizedTask(final int taskId) {
     synchronized (lock[taskId % lock.length]) {
     return ioBoundTask();
     }
     }
     synchronized
     will block
     the carrier thread
     

     View Slide

196. JDK 21: Virtual Threads
     The synchronized keyword
     private final static Object[] lock = new Object[4];
     static {
     for (int i = 0; i < lock.length; ++i) {
     lock[i] = new Object();
     }
     }
     private static long ioSynchronizedTask(final int taskId) {
     synchronized (lock[taskId % lock.length]) {
     return ioBoundTask();
     }
     }
     Multiple synchronized Object
     Will not help
     If you are lucky
     You’ll get the
     CPU Bound Task Behaviour
     Even on I/O Operations
     

     View Slide

197. JDK 21: Virtual Threads
     The synchronized keyword
     private final static Object[] lock = new Object[4];
     static {
     for (int i = 0; i < lock.length; ++i) {
     lock[i] = new Object();
     }
     }
     private static long ioSynchronizedTask(final int taskId) {
     synchronized (lock[taskId % lock.length]) {
     return ioBoundTask();
     }
     }
     Remove the use of
     Synchronized
     

     View Slide

198. JDK 21: Virtual Threads
     Locks: Reentrant Lock, Semaphores, …
     private static final ReentrantLock[] rlock = new ReentrantLock[4];
     static {
     for (int i = 0; i < rlock.length; ++i) {
     rlock[i] = new ReentrantLock();
     }
     }
     private static long ioLockedTask(final int taskId) {
     final ReentrantLock lock = rlock[taskId % rlock.length];
     lock.lock();
     try {
     return ioBoundTask(); // http.send(), sleep(), ...
     } finally {
     lock.unlock();
     }
     }
     // Run with -Djdk.virtualThreadScheduler.parallelism=1
     final long startTime = System.nanoTime();
     try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
     for (int i = 0; i < 10; ++i) {
     final int taskId = i;
     executor.submit(() -> {
     ioLockedTask();
     long elapsedNs = System.nanoTime() - startTime;
     });
     }
     }
     4 Tasks will run concurrently
     Locks are a blocking operation
     Releasing the Virtual Thread from the Carrier
     

     View Slide

199. JDK 21
     Virtual Threads
     Do not go and replace all your ExecutorServices with Virtual Threads!
     CPU Bound Tasks will not benefit from it
     Virtual Threads are made for I/O bound Tasks
     Spends most of the time
     using CPU
     Spends most of the time
     waiting for I/O
     Longer CPU bursts Shorter CPU bursts
     CPU Bound I/O Bound
     

     View Slide

200. JDK 21
     Virtual Threads
     Do not go and replace all your ExecutorServices with Virtual Threads!
     CPU Bound Tasks will not benefit from it
     Virtual Threads are made for I/O bound Tasks
     Spends most of the time
     using CPU
     Spends most of the time
     waiting for I/O
     Longer CPU bursts Shorter CPU bursts
     CPU Bound I/O Bound
     Virtual
     Threads
     A Service or a Database
     

     View Slide

201. JDK 21
     Virtual Threads
     Do not go and replace all your ExecutorServices with Virtual Threads!
     CPU Bound Tasks will not benefit from it
     Virtual Threads are made for I/O bound Tasks
     Spends most of the time
     using CPU
     Spends most of the time
     waiting for I/O
     Longer CPU bursts Shorter CPU bursts
     CPU Bound I/O Bound
     Virtual
     Threads
     A Service or a Database
     Can your Database, Service, Disk, …
     handle the extra concurrency?
     (Probably not)
     If you are using Virtual Threads
     You should limit the access
     To a Resource
     Using a Semaphore (or similar)
     

     View Slide