If you ever wrote concurrent code in Java, you probably used some of its concurrency primitives. It might surprise you that Kotlin doesn’t have any constructs for dealing with concurrency as part of the language. The Kotlin design team felt that this should be the job of libraries. The Kotlin standard library has, in the base kotlin package and the kotlin.concurrent package, several functions, and annotations that can compile to Java's concurrency primitives.
Concurrent programming is a huge topic and we could write an entire book about it. So in this section, we’ll cover only what Kotlin has to offer for concurrent programming.
