Kotlin coroutines: design and implementation

Asynchronous programming is having its “renaissance” moment in recent years. Since the 2000s, more and more programming languages have begun to include the support for asynchronous programming, some built around asynchronicity from the start, others including it later in their evolution. In this paper, we explore the design and implementation of asynchronous programming in Kotlin,which uses coroutines for asynchronicity. Kotlin provides a compact built-in API for coroutine support, giving a lot of implementation freedom to the developer; this flexibility allows to transparently support different flavours of asynchronous programming within the same language. We overview existing approaches to asynchronous programming, talk about coroutines in detail, and describe how they are used in Kotlin as the basis for asynchronous computations.