How to create a `CoroutineScope` that is a child of another kotlinlang #coroutines

val parentScope = ...
val childScope = parentScope + SupervisorJob()

parentScope.cancel()
parentScope.isActive // false
childScope.isActive // true (!!)

It seems that cancelling the parent does not cancel its children. I guess I'm missing something here...

bezrukov

03/11/2020, 4:49 PM

val childScope = parentScope + SupervisorJob(parentScope.coroutineContext[Job])

it attaches child job to parent job

Javier Troconis

03/11/2020, 5:01 PM

Woudln't this make them siblings rather than enforce a parent-child hierarchy?

Dennis

03/11/2020, 5:05 PM

Isn't it just either

coroutineScope

(doc) or

supervisorScope

(doc)

Well this doesn't return the scope to you, right.

bezrukov

03/11/2020, 5:14 PM

@Javier Troconis nope, it will be parent-child hierarchy, if you cancel childScope, parentScope will be active active. From the SupervisorJob doc:

* If [parent] job is specified, then this supervisor job becomes a child job of its parent and is cancelled when its parent fails or is cancelled. All this supervisor's children are cancelled in this case, too. The invocation of [cancel][Job.cancel] with exception (other than [CancellationException]) on this supervisor job also cancels parent.

👍 1

Javier Troconis

03/11/2020, 5:28 PM

Thanks @bezrukov. Thought that it was simply setting the job itself and not the parent

tseisel

03/11/2020, 7:24 PM

Indeed, that was the missing part! I expected the child scope to directly inherit the job of its parent. It seems that this parent-child relationship should be explicitly defined

bezrukov

03/11/2020, 7:47 PM

I think it's impossible because constructor can't be suspend, and there is no access to coroutineContext from non-suspend block.

3 Views

#coroutines Join Slack