I have a question about `SupervisorJob`. This code...

# coroutines

[streetsofboston]

I have a question about SupervisorJob.
This code

CoroutineScope(SupervisorJob()).launch {
    launch { 
        println("Launched Child 1")
        delay(500)
        println("Child 1 crashed")
        throw SillyException()
    }

    launch {
        println("Launched Child 2")
        delay(1000)
        println("Child 2 is still running")
        delay(500)
    }

    delay(1000)
    println("Parent is still running")
}

Thread.sleep(2000)

prints out this:

Launched Child 1
Launched Child 2
Child 1 crashed
Exception in thread "DefaultDispatcher-worker-2 @coroutine#3" launch_exceptions.SillyException: Silly
	at launch_exceptions.FileKt$main$1$1.invokeSuspend(File.kt:20)
        ...

I expected only “Child 1” to crash/stop, due to the parent being a Supervisor-Job .
However, I expected “Child 2" launch and the parent to continue running…
especially since MainScope() is defined in a similar way…

[Evgeniy Zaharov]

inner launch is start as child for outer launch, which is not a SupervisorJob. Only childs of CoroutineScope(SupervisorJob()) fails independently from each other

[streetsofboston]

I see. Thank you, @Evgeniy Zaharov ! You say that this would work:

val scope = CoroutineScope(SupervisorJob())
scope.launch { 
    println("Launched Child 1")
    delay(500)
    println("Child 1 crashed")
    throw SillyException()
}

scope.launch {
    println("Launched Child 2")
    delay(1000)
    println("Child 2 is still running")
    delay(500)
}

[louiscad]

You could use supervisorScope { … } also, and launch all the coroutines here.

[streetsofboston]

Thanks!
But not always, though. The function supervisorScope is a suspend fun and can’t be called from a regular non-suspending function.

[streetsofboston]

But it is a handy function to move a sub-tree of your coroutine scope’s children within a SupervisorJob. 🙂

[Dico]

Perhaps it would work if you used the coroutine context parameter instead of the scope