Introduction to stackless coroutines

So, we’ve finally arrived at the point where we introduce the last method of modeling asynchronous operations in this book. You probably remember that we gave a high-level overview of stackful and stackless coroutines in Chapter 2. In Chapter 5, we implemented an example of stackful coroutines when writing our own fibers/green threads, so now it’s time to take a closer look at how stackless coroutines are implemented and used.

A stackless coroutine is a way of representing a task that can be interrupted and resumed. If you remember all the way back in Chapter 1, we mentioned that if we want tasks to run concurrently (be in progress at the same time) but not necessarily in parallel, we need to be able to pause and resume the task.

In its simplest form, a coroutine is just a task that can stop and resume by yielding control to either its caller, another coroutine, or a scheduler.

Many languages will have a coroutine implementation...