Continuations: The magic behind virtual threads in Java

Balkrishna Rawool - ING Bank NV

Have you wondered how virtual threads in Java are able to provide such high scalability? How is JVM able to switch between so many virtual threads while executing a single platform thread? If you did then this talk is for you.

A Continuation is the magic that powers Virtual Threads. It can be viewed as a representation of the current state of the program or it can be viewed as a reference to the rest of the program. It helps us to pause execution of a program (or part thereof) and then resume it later. This ability to pause/resume is a powerful mechanism and is the basis for providing virtual threads.

In this talk, we will start with explaining what continuations are and how does Continuation API in Java work. We will also explore the uses of continuations. And more importantly, we will write our own simple VirtualThread class using the Continuation API provided by JDK. This gives clear idea about the role of continuations in the nature of virtual threads.