Continuations: The Magic Behind Virtual Threads - Spring IO

Transcript

1. 30 May 2024 Balkrishna Rawool Continuations The magic behind virtual threads
2. 2 Balkrishna Rawool IT Chapter Lead, ING Bank @BalaRawool
3. Introduction to Virtual Threads
4. 4 Platform Threads and Virtual Threads JVM OS Platform Threads Platform Threads: Ø Thin wrapper over OS threads Ø One-to-one mapping with OS threads Ø Thread pools Virtual Threads Virtual Threads: Ø Lightweight user threads Ø Highly scalable Ø No need for pooling
5. 5 Virtual Thread Scheduler Platform/ Carrier Thread Virtual Threads
6. How to create virtual threads?
7. Continuations
8. Continuation 8 Ø A continuation can be viewed as Ø A representation of the current state of the program
9. Continuation 9 Ø A continuation can be viewed as Ø A representation of the current state of the program or Ø “The rest of the computation” Ø It allows us to pause execution of a program (or part thereof) and resume it later. Ø Continuations in Java Ø WARNING: Continuation API in Java is not supposed to be used directly by application developers. For now, it is only used internally to implement virtual threads.
10. Continuations in Java
11. cont Continuations in Java 12 Continuation.yield() Cont.yield() d() c() b() cont.run() a() main() Stack Heap d() c() b() cont.run() a() main() Stack Heap Cont.yield()
12. Continuations in Java 13 Continuation.run() c() b() cont.run() e() main() Stack Heap d() c() b() cont.run() e() main() Stack Heap Cont.yield() Cont.yield() d() cont cont
13. Uses of continuations 14 Ø Virtual threads or green threads Ø Coroutines Ø Exception handling Ø Generators
14. Generator 15 Ø A generator allows us to write a function that ‘yields’ values. Ø These values are lazily retrieved. Ø They can then be iterated over by using a loop. { //… //… yield “A”; //… //… yield “B”; //… //… yield “C”; } Generator while () { // … } Consumer
15. Generator using Continuations
16. A Simple VirtualThread using Continuations
17. Simple VirtualThread 18 Ø Goals Ø A VirtualThread instance should not use CPU (or platform thread) when waiting/ blocking. Ø A VirtualThread can get mounted on several platform threads during its lifetime. Ø A platform thread can support several VirtualThread-s during its lifetime.
18. Simple VirtualThread 19 VirtualThread VirtualThreadScheduler Virtual threads Platform threads // Consumer { // … // Blocking call // … }
19. Source code and contact 20 @BalaRawool