kotlinx.coroutines

Three libraries built upon Kotlin coroutines:

kotlinx-coroutines-async with convenient interfaces/wrappers to commonly used asynchronous API shipped with standard JDK, namely promise-like CompletableFuture and asynchronous channels from java.nio package
kotlinx-coroutines-generate provides ability to create Sequence objects generated by coroutine body containing yield suspension points
kotlinx-coroutines-rx allows to use Observable objects from RxJava inside a coroutine body to suspend on them

Examples

Async

import kotlinx.coroutines.async
import java.util.concurrent.CompletableFuture

private fun startLongAsyncOperation(v: Int) =
        CompletableFuture.supplyAsync {
            Thread.sleep(1000)
            "Result: $v"
        }

fun main(args: Array<String>) {
    val future = async {
        (1..5).map {
            startLongAsyncOperation(it).await()
        }.joinToString("\n")
    }

    println(future.get())
}

Bear in mind that async library actively uses CompletableFuture from JDK 8, so it will not work with earlier versions.

Generate

import kotlinx.coroutines.generate

fun main(args: Array<String>) {
    val sequence = generate {
        for (i in 1..5) {
            yield(i)
        }
    }

    println(sequence.joinToString(" "))
}

RxJava

import kotlinx.coroutines.asyncRx
import retrofit2.Retrofit
import retrofit2.adapter.rxjava.RxJavaCallAdapterFactory
import retrofit2.converter.gson.GsonConverterFactory
import retrofit2.http.GET
import retrofit2.http.Path
import rx.Observable

interface GitHub {
    @GET("orgs/{user}/repos")
    fun orgRepos(@Path("user") user: String): Observable<List<Repo>>
}

data class Repo(val name: String)

fun main(args: Array<String>) {
    val retrofit = Retrofit.Builder().apply {
        baseUrl("https://api.github.com")
        addConverterFactory(GsonConverterFactory.create())
        addCallAdapterFactory(RxJavaCallAdapterFactory.create())
    }.build()

    val github = retrofit.create(GitHub::class.java)

    asyncRx {
        for (org in listOf("Kotlin", "ReactiveX")) {
            // `awaitSingle()` call here is a suspension point,
            // i.e. coroutine's code stops on it until request is not completed
            val repos = github.orgRepos(org).take(5).awaitSingle().joinToString()

            println("$org: $repos")
        }
    }
}

For more examples you can look at kotlinx-coroutines-async-example-ui and kotlinx-coroutines-rx-example samples projects or in tests directories.

Using in your projects

Note that these libraries are experimental and are subject to change.

The libraries are published to kotlin-eap-1.1 bintray repository.

These libraries require kotlin compiler version to be at least 1.1-M04 and require kotlin runtime of the same version as a dependency, which can be obtained from the same repository.

Maven

Add the bintray repository to <repositories> section (and also add pluginRepository to <pluginRepositories>, if you're willing to get kotlin-maven-plugin from there):

<repository>
    <snapshots>
        <enabled>false</enabled>
    </snapshots>
    <id>dl</id>
    <name>bintray</name>
    <url>http://dl.bintray.com/kotlin/kotlin-eap-1.1</url>
</repository>

Add dependencies (you can add just those of them that you need):

<dependency>
    <groupId>org.jetbrains.kotlinx</groupId>
    <artifactId>kotlinx-coroutines-generate</artifactId>
    <version>0.2-beta</version>
</dependency>
<dependency>
    <groupId>org.jetbrains.kotlinx</groupId>
    <artifactId>kotlinx-coroutines-async</artifactId>
    <version>0.2-beta</version>
</dependency>
<dependency>
    <groupId>org.jetbrains.kotlinx</groupId>
    <artifactId>kotlinx-coroutines-rx</artifactId>
    <version>0.2-beta</version>
</dependency>

Gradle

Add the bintray repository (and also add it to buildScript section, if you're willing to get kotlin-gradle-plugin from there):

repositories {
    maven {
        url "http://dl.bintray.com/kotlin/kotlin-eap-1.1"
    }
}