Child coroutine scope

What is the recommended pattern from within a suspend function to launch a new child coroutine from the current scope?

I want to ensure that cancelling the parent scope cancels any coroutines launched by the child scopes.

Is the below the best practice for achieving this?

suspend fun refresh() {
    // need to build a new coroutine scope that is the child of the current coroutine scope (from `suspend`)
    coroutineScope {  // <-- child scope
        val task1 = async { } // some async task
        val task2 = async { } // some async task
        awaitAll(task1, task2)
    }
}
suspend fun example(scope: CoroutineScope) {
    scope.launch { refresh() }
    // will cancelling this job cancel the two async tasks in `refresh()` if they have not completed yet?
    scope.coroutineContext[Job]!!.cancel()
}

[fvasco]

I rewrote your example using an explicit job

suspend fun refresh() {
    // need to build a new coroutine scope that is the child of the current coroutine scope (from `suspend`)
    coroutineScope {
        // <-- child scope
        val task1 = async {
            try {
                println("task1 started")
                delay(100000)
            } catch (e: CancellationException) {
                println("task1 cancelled")
            }

        } // some async task
        val task2 = async { } // some async task
        awaitAll(task1, task2)
    }
}

suspend fun example() {
    val job = Job()
    withContext(job) {
        launch { refresh() }
        // await `launch` initialization or start it UNDISPATCHED
        delay(1000)
        // will cancelling this job cancel the two async tasks in `refresh()` if they have not completed yet?
        job.cancel()
    }
}

The output is

task1 started
task1 cancelled
Exception in thread "main" kotlinx.coroutines.experimental.JobCancellationException: Job was cancelled; job=JobImpl{Cancelled}@71423665

Process finished with exit code 1

[elizarov]

What you are trying to achieve here? Can you, please, give little bit more details about your problem and the context of what you are trying to do. Why do you have suspend fun that is also returning a Deferred. What is the purpose?