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Library support for Kotlin coroutines

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Quick Overview

Kotlinx.coroutines is a rich library for Kotlin coroutines with multiplatform support. It provides high-level coroutine-enabled primitives including launch, async, and more. The library is designed to simplify asynchronous programming and make concurrent code more readable and maintainable.

Pros

  • Simplifies asynchronous and concurrent programming in Kotlin
  • Supports multiple platforms (JVM, JavaScript, Native)
  • Provides a wide range of coroutine-based utilities and patterns
  • Excellent integration with other Kotlin libraries and frameworks

Cons

  • Learning curve for developers new to coroutines
  • Potential for misuse leading to performance issues if not used correctly
  • Debugging coroutine-based code can be challenging
  • Some advanced features may require in-depth understanding of coroutines

Code Examples

  1. Basic coroutine launch:
import kotlinx.coroutines.*

fun main() = runBlocking {
    launch {
        delay(1000L)
        println("World!")
    }
    println("Hello,")
}

This example launches a coroutine that prints "World!" after a 1-second delay, while the main coroutine immediately prints "Hello,".

  1. Async/await pattern:
import kotlinx.coroutines.*

suspend fun fetchUserData(): String {
    delay(1000L) // Simulating network request
    return "User data"
}

suspend fun fetchUserPosts(): List<String> {
    delay(1000L) // Simulating network request
    return listOf("Post 1", "Post 2")
}

fun main() = runBlocking {
    val userData = async { fetchUserData() }
    val userPosts = async { fetchUserPosts() }
    
    println("User: ${userData.await()}")
    println("Posts: ${userPosts.await()}")
}

This example demonstrates concurrent execution of two suspending functions using async, and then awaiting their results.

  1. Flow usage:
import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*

fun numbers(): Flow<Int> = flow {
    for (i in 1..3) {
        delay(100)
        emit(i)
    }
}

fun main() = runBlocking {
    numbers()
        .map { it * it }
        .collect { println(it) }
}

This example shows how to create and use a Flow to emit a sequence of values asynchronously.

Getting Started

To use kotlinx.coroutines in your project, add the following dependency to your build.gradle file:

dependencies {
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.1")
}

For Android projects, you may also want to add:

implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.7.1")

Then, you can start using coroutines in your Kotlin code by importing the necessary functions and classes from the kotlinx.coroutines package.

Competitor Comparisons

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RxJava

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RxJava – Reactive Extensions for the JVM – a library for composing asynchronous and event-based programs using observable sequences for the Java VM.

Pros of RxJava

  • More mature and widely adopted in the Java ecosystem
  • Extensive set of operators for complex data transformations
  • Better support for backpressure handling

Cons of RxJava

  • Steeper learning curve due to its complexity
  • Can lead to callback hell in nested operations
  • Less intuitive for developers new to reactive programming

Code Comparison

RxJava:

Observable.just(1, 2, 3)
    .map(i -> i * 2)
    .subscribe(System.out::println);

kotlinx.coroutines:

launch {
    listOf(1, 2, 3).map { it * 2 }
        .forEach { println(it) }
}

RxJava offers a rich set of operators and is well-established in the Java ecosystem. It excels in handling complex data streams and backpressure scenarios. However, it can be challenging for newcomers and may lead to convoluted code in nested operations.

kotlinx.coroutines, on the other hand, provides a more straightforward approach to asynchronous programming. It integrates seamlessly with Kotlin's language features, making it easier to write and understand concurrent code. While it may not have as many specialized operators as RxJava, it offers a more intuitive API for most common use cases.

The code comparison demonstrates the difference in syntax and approach. RxJava uses a chain of operators, while kotlinx.coroutines leverages Kotlin's built-in functions within a coroutine scope, resulting in more readable and concise code.

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RxKotlin

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Pros of RxKotlin

  • Extensive set of operators for complex data transformations
  • Cross-platform support (Android, iOS, web)
  • Well-established ecosystem with many resources and libraries

Cons of RxKotlin

  • Steeper learning curve due to its functional reactive paradigm
  • Can lead to callback hell if not used carefully
  • Heavier memory footprint compared to coroutines

Code Comparison

RxKotlin:

Observable.just(1, 2, 3)
    .map { it * 2 }
    .subscribe { println(it) }

kotlinx.coroutines:

launch {
    listOf(1, 2, 3).forEach {
        println(it * 2)
    }
}

Summary

RxKotlin offers powerful reactive programming capabilities with a rich set of operators, making it suitable for complex data streams and cross-platform development. However, it can be more challenging to learn and may lead to callback-heavy code.

kotlinx.coroutines provides a more straightforward approach to asynchronous programming, integrating seamlessly with Kotlin's language features. It has a gentler learning curve and generally results in more readable code, but may have fewer built-in operators for complex data transformations compared to RxKotlin.

The choice between the two depends on project requirements, team expertise, and the specific use case at hand.

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README

kotlinx.coroutines

Kotlin Stable JetBrains official project GitHub license Download Kotlin Slack channel

Library support for Kotlin coroutines with multiplatform support. This is a companion version for the Kotlin 2.0.0 release.

suspend fun main() = coroutineScope {
    launch { 
       delay(1000)
       println("Kotlin Coroutines World!") 
    }
    println("Hello")
}

Play with coroutines online here

Modules

Documentation

Using in your projects

Maven

Add dependencies (you can also add other modules that you need):

<dependency>
    <groupId>org.jetbrains.kotlinx</groupId>
    <artifactId>kotlinx-coroutines-core</artifactId>
    <version>1.9.0-RC.2</version>
</dependency>

And make sure that you use the latest Kotlin version:

<properties>
    <kotlin.version>2.0.0</kotlin.version>
</properties>

Gradle

Add dependencies (you can also add other modules that you need):

dependencies {
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.9.0-RC.2")
}

And make sure that you use the latest Kotlin version:

plugins {
    // For build.gradle.kts (Kotlin DSL)
    kotlin("jvm") version "2.0.0"
    
    // For build.gradle (Groovy DSL)
    id "org.jetbrains.kotlin.jvm" version "2.0.0"
}

Make sure that you have mavenCentral() in the list of repositories:

repositories {
    mavenCentral()
}

Android

Add kotlinx-coroutines-android module as a dependency when using kotlinx.coroutines on Android:

implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.9.0-RC.2")

This gives you access to the Android Dispatchers.Main coroutine dispatcher and also makes sure that in case of a crashed coroutine with an unhandled exception that this exception is logged before crashing the Android application, similarly to the way uncaught exceptions in threads are handled by the Android runtime.

R8 and ProGuard

R8 and ProGuard rules are bundled into the kotlinx-coroutines-android module. For more details see "Optimization" section for Android.

Avoiding including the debug infrastructure in the resulting APK

The kotlinx-coroutines-core artifact contains a resource file that is not required for the coroutines to operate normally and is only used by the debugger. To exclude it at no loss of functionality, add the following snippet to the android block in your Gradle file for the application subproject:

packagingOptions {
    resources.excludes += "DebugProbesKt.bin"
}

Multiplatform

Core modules of kotlinx.coroutines are also available for Kotlin/JS and Kotlin/Native.

In common code that should get compiled for different platforms, you can add a dependency to kotlinx-coroutines-core right to the commonMain source set:

commonMain {
    dependencies {
        implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.9.0-RC.2")
    }
}

Platform-specific dependencies are recommended to be used only for non-multiplatform projects that are compiled only for target platform.

JS

Kotlin/JS version of kotlinx.coroutines is published as kotlinx-coroutines-core-js (follow the link to get the dependency declaration snippet).

Native

Kotlin/Native version of kotlinx.coroutines is published as kotlinx-coroutines-core-$platform where $platform is the target Kotlin/Native platform. Targets are provided in accordance with official K/N target support.

Building and Contributing

See Contributing Guidelines.