Mastering Concurrency in Kotlin

By John Doe — Published on October 26, 2023

Kotlin’s approach to concurrency is a game-changer for modern application development. By leveraging coroutines, Kotlin provides a powerful yet simple way to write asynchronous, non-blocking code.This article dives deep into the core concepts of Kotlin concurrency, exploring how to write efficient, scalable, and readable concurrent code.

We’ll start with the basics of coroutines — understanding what they are and how they differ from traditional threads. Then, we will explore structured concurrency, a key feature that simplifies handling concurrent tasks and prevents resource leaks.

Introduction to Coroutines

Coroutines are light-weight threads.
They are launched within a CoroutineScope.
You can create a new coroutine using coroutine builders such as launch or async.

Example

import kotlinx.coroutines.*

fun main() = runBlocking { // this: CoroutineScope
    launch { // launch a new coroutine and continue
        delay(1000L) // non-blocking delay for 1 second (default time unit is ms)
        println("World!") // print after delay
    }
    println("Hello,") // main coroutine continues while a previous one is delayed
}

Structured Concurrency

Structured concurrency is a combination of language features and best practices that ensure coroutines are launched in a specific CoroutineScope.

This scope is responsible for all the coroutines it creates. If the scope is cancelled, all coroutines within it are cancelled as well.

Example

import kotlinx.coroutines.*

fun main() = runBlocking { // this: CoroutineScope
    val job = launch { // launch a new coroutine and keep a reference to its Job
        delay(1000L)
        println("World!")
    }
    println("Hello, ")
    job.join() // wait until child coroutine completes
    println("Done")
}

suspend fun doWorld() = coroutineScope { // this: CoroutineScope
    launch {
        delay(2000L)
        println("World 2")
    }
    launch {
        delay(1000L)
        println("World 1")
    }
    println("Hello")
}