Continuations The Magic Behind Virtual Threads

Transcript

1. Alignment indicator 10 Jan 2024 Balkrishna Rawool Continuations The magic behind virtual threads
2. 2 Balkrishna Rawool IT Chapter Lead, Business Lending @BalaRawool
3. Alignment indicator Virtual Threads
4. 4 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. Alignment indicator How to create virtual threads?
7. Alignment indicator 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 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. Alignment indicator Continuations in Java
11. 11 Continuations in Java are One Shot Multi-Prompt Delimited Continuations
12. Continuations in Java 12 Continuation.yield() yield() d() c() b() run() a() main() Stack Heap d() c() b() run() a() main() Stack Heap yield()
13. Continuations in Java 13 Continuation.run() c() b() run() a() main() Stack Heap d() c() b() run() a() main() Stack Heap yield() yield() d()
14. Uses of continuations 14 Ø Green threads or virtual threads Ø Coroutines Ø Exception handling Ø Generators
15. 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 1; //… //… yield 2; //… //… yield 3; //… //… yield 4; } Generator while () { // … } Consumer
16. Alignment indicator Generator using Continuations
17. Alignment indicator A Simple VirtualThread using Continuations
18. 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.
19. Simple VirtualThread 19 VirtualThread VirtualThreadScheduler Virtual threads Platform threads // Consumer { // … // Blocking call // … }
20. Source code 20 github.com/balkrishnarawool
21. Connect with me at 21 @BalaRawool