Programming Android with Kotlin

Chapter 9. Channels

In the previous chapter, you learned how to create coroutines, cancel them, and deal with exceptions. So you know that if task B requires the result of task A, you can implement them as two suspending functions called sequentially. What if task A produces a stream of values? async and suspending functions don’t fit this use case. This is what Channels¹ are meant for—making coroutines communicate. In this chapter you’ll learn in detail what channels are and how to use them.

Using nothing but channels and coroutines, we can design complex asynchronous logic using communicating sequential processes (CSP). What is CSP? Kotlin was inspired by several existing programming languages, such as Java, C#, JavaScript, Scala, and Groovy. Notably, Go (the language) inspired coroutines with its “goroutines.”

In computer science, CSP is a concurrent programming language which was first described by Tony Hoare in 1978. It has evolved ever since, and the term CSP is now essentially used to describe a programming style. If you’re familiar with the Actor model, CSP is quite similar—although there are some differences. If you’ve never heard of CSP, don’t worry—we’ll briefly explain the idea behind it with practical examples. For now, you can think of CSP as a programming style.

As usual, we’ll start with a bit of theory, then implement a real-life problem. In the end, we’ll discuss the benefits and trade-offs of CSP, using coroutines.

Channels Overview

Going back to our introductory ...