Implementing coroutines in Java

Question

This question is related to my question on existing coroutine implementations in Java. If, as I suspect, it turns out that there is no full implementation of coroutines cur

Answer 1

Kotlin uses the following approach for co-routines
(from https://kotlinlang.org/docs/reference/coroutines.html):

Coroutines are completely implemented through a compilation technique (no support from the VM or OS side is required), and suspension works through code transformation. Basically, every suspending function (optimizations may apply, but we'll not go into this here) is transformed to a state machine where states correspond to suspending calls. Right before a suspension, the next state is stored in a field of a compiler-generated class along with relevant local variables, etc. Upon resumption of that coroutine, local variables are restored and the state machine proceeds from the state right after suspension.

A suspended coroutine can be stored and passed around as an object that keeps its suspended state and locals. The type of such objects is Continuation, and the overall code transformation described here corresponds to the classical Continuation-passing style. Consequently, suspending functions take an extra parameter of type Continuation under the hood.

Check out the design document at https://github.com/Kotlin/kotlin-coroutines/blob/master/kotlin-coroutines-informal.md