kotlinx.coroutines

Library support for Kotlin coroutines with multiplatform support. This is a companion version for Kotlin 1.3.71 release.

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

Play with coroutines online here

Modules

• core — common coroutines across all platforms:
  • launch and async coroutine builders returning Job and Deferred light-weight futures with cancellation support;
  • Dispatchers object with Main dispatcher for Android/Swing/JavaFx, and Default dispatcher for background coroutines;
  • delay and yield top-level suspending functions;
  • Flow — cold asynchronous stream with flow builder and comprehensive operator set (filter, map, etc);
  • Channel, Mutex, and Semaphore communication and synchronization primitives;
  • coroutineScope, supervisorScope, withContext, and withTimeout scope builders;
  • MainScope() for Android and UI applications;
  • SupervisorJob() and CoroutineExceptionHandler for supervision of coroutines hierarchies;
  • select expression support and more.
• core/jvm — additional core features available on Kotlin/JVM:
  • Dispatchers.IO dispatcher for blocking coroutines;
  • Executor.asCoroutineDispatcher extension, custom thread pools, and more.
• core/js — additional core features available on Kotlin/JS:
  • Integration with Promise via Promise.await and promise builder;
  • Integration with Window via Window.asCoroutineDispatcher, etc.
• test — test utilities for coroutines:
  • Dispatchers.setMain to override Dispatchers.Main in tests;
  • TestCoroutineScope to test suspending functions and coroutines.
• debug — debug utilities for coroutines:
  • DebugProbes API to probe, keep track of, print and dump active coroutines;
  • CoroutinesTimeout test rule to automatically dump coroutines on test timeout.
• reactive — modules that provide builders and iteration support for various reactive streams libraries:
  • Reactive Streams (Publisher.collect, Publisher.awaitSingle, publish, etc),
  • Flow (JDK 9) (the same interface as for Reactive Streams),
  • RxJava 2.x (rxFlowable, rxSingle, etc), and
  • RxJava 3.x (rxFlowable, rxSingle, etc), and
  • Project Reactor (flux, mono, etc).
• ui — modules that provide coroutine dispatchers for various single-threaded UI libraries:
  • Android, JavaFX, and Swing.
• integration — modules that provide integration with various asynchronous callback- and future-based libraries:
  • JDK8 CompletionStage.await, Guava ListenableFuture.await, and Google Play Services Task.await;
  • SLF4J MDC integration via MDCContext.

Documentation

• Presentations and videos:
  • Introduction to Coroutines (Roman Elizarov at KotlinConf 2017, slides)
  • Deep dive into Coroutines (Roman Elizarov at KotlinConf 2017, slides)
  • Kotlin Coroutines in Practice (Roman Elizarov at KotlinConf 2018, slides)
• Guides and manuals:
  • Guide to kotlinx.coroutines by example (read it first)
  • Guide to UI programming with coroutines
  • Debugging capabilities in kotlinx.coroutines
• Compatibility policy and experimental annotations
• Change log for kotlinx.coroutines
• Coroutines design document (KEEP)
• Full kotlinx.coroutines API reference

Using in your projects

The libraries are published to kotlinx bintray repository, linked to JCenter and pushed to Maven Central.

Maven

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

<dependency>
    <groupId>org.jetbrains.kotlinx</groupId>
    <artifactId>kotlinx-coroutines-core</artifactId>
    <version>1.3.5</version>
</dependency>

And make sure that you use the latest Kotlin version:

<properties>
    <kotlin.version>1.3.71</kotlin.version>
</properties>

Gradle

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

dependencies {
    implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.5'
}

And make sure that you use the latest Kotlin version:

buildscript {
    ext.kotlin_version = '1.3.71'
}

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

repository {
    jcenter()
}

Gradle Kotlin DSL

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

dependencies {
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.5")
}

And make sure that you use the latest Kotlin version:

plugins {
    kotlin("jvm") version "1.3.71"
}

Make sure that you have either jcenter() or mavenCentral() in the list of repositories.

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, add dependency to
kotlinx-coroutines-core-common
(follow the link to get the dependency declaration snippet).

Android

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

implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.5'

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

JS

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

You can also use kotlinx-coroutines-core package via NPM.

Native

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

Only single-threaded code (JS-style) on Kotlin/Native is currently supported. Kotlin/Native supports only Gradle version 4.10 and you need to enable Gradle metadata in your settings.gradle file:

enableFeaturePreview('GRADLE_METADATA')

Since Kotlin/Native does not generally provide binary compatibility between versions, you should use the same version of Kotlin/Native compiler as was used to build kotlinx.coroutines.

Building

This library is built with Gradle. To build it, use ./gradlew build. You can import this project into IDEA, but you have to delegate build actions to Gradle (in Preferences -> Build, Execution, Deployment -> Build Tools -> Gradle -> Runner)

Requirements

• JDK >= 11 referred to by the JAVA_HOME environment variable.
• JDK 1.6 referred to by the JDK_16 environment variable. It is okay to have JDK_16 pointing to JAVA_HOME for external contributions.
• JDK 1.8 referred to by the JDK_18 environment variable. Only used by nightly stress-tests. It is okay to have JDK_18 pointing to JAVA_HOME for external contributions.

Contributions and releases

All development (both new features and bug fixes) is performed in develop branch. This way master sources always contain sources of the most recently released version. Please send PRs with bug fixes to develop branch. Fixes to documentation in markdown files are an exception to this rule. They are updated directly in master.

The develop branch is pushed to master during release.

• Full release procedure checklist is here.
• Steps for contributing new integration modules are explained here.
• Use Knit for updates to documentation:
  • In project root directory run ./gradlew knit.
  • Commit updated documents and examples together with other changes.
• Use Binary Compatibility Validator for updates to public API:
  • In project root directory run ./gradlew apiDump.
  • Commit updated API index together with other changes.