Example of structured concurrency in Kotlin

kotlinStructuredConcurrency.kt

import kotlinx.coroutines.experimental.*
import kotlinx.coroutines.experimental.channels.Channel
import java.util.*

/*
 * Structured concurrency means that child co-routines should die when their father dies
 * http://libdill.org//structured-concurrency.html
 *
 * In kotlin in order to have parent->child relationship you need to explicitly pass
 * the coroutineContext to the child coroutine.
 */

fun main(args: Array<String>) = runBlocking<Unit> {

    println("Main: context ${coroutineContext}")

    val father = launch(coroutineContext) {

        println("Father: context ${coroutineContext}")

        launch(coroutineContext) {

            println("Child: context ${coroutineContext}")

            do {
                println("Child: is alive")
                delay(1000)
            } while (true)

        }

        // Father is not actually dead until `father.cancel()` because the child
        // is keeping it alive. Here we could also use
        // coroutineContext.cancel() or coroutineContext.cancelChildren()

    }

    delay(3000)
    print("Main: killing father")
    father.cancel()
    delay(3000)
    print("Main: is done")

}

output:

Main: context [BlockingCoroutine{Active}@66d33a, BlockingEventLoop@7cf10a6f]
Father: context [StandaloneCoroutine{Active}@35f983a6, BlockingEventLoop@7cf10a6f]
Child: context [StandaloneCoroutine{Active}@6cd8737, BlockingEventLoop@7cf10a6f]
Child: is alive
Child: is alive
Child: is alive
Main: killing father
Main: is done