I have a long running operation which I start from my `viewModelScope`. When the viewmodel gets dest...

# coroutines

[voben]

I have a long running operation which I start from my viewModelScope. When the viewmodel gets destroyed before the long running operation finishes, the function println(“Hello World”) is still getting called. Wouldn’t the coroutine get cancelled and not print “Hello World” due to structured concurrency?

viewModelScope.launch {
        doLongRunningOperation()
}

suspend fun doLongRunningOperation() = withContext(Dispatchers.Default) {
        longRunningCalculation() // Not a suspending function
        println("Hello World")
    }

[rook]

I think that your withContext(Dispatchers.Default) starts your long running operation off of `viewModelScope`’s context

[rook]

suspend fun doLongRunningOperation() {
  longRunningCalculation()
  println("HelloWorld")
}

[voben]

but I need to run the long running operation off of the main thread. I don’t see why having another Dispatcher would be the issue

[Lou Morda]

cancel it in onCleared()?

[voben]

cancel already gets called onCleared

[louiscad]

Blocking code is not cancellable, unless you go into a specific (and complicated) integration with coroutines cancellation.

[reline]

Use isActive to check if the coroutine is not cancelled before performing some action

[louiscad]

withContext already checks for cancellation on enter and exit

[reline]

Yeah, I meant after his blocking operation he could check before println()

[Jonathan Walsh]

couldn't you also add checks for isActive inside the longRunningCalculation() if that is doing CPU work and not just blocked on IO?

[Dominaezzz]

isActive only works in suspend functions, although you could pass in the context I guess.

[louiscad]

Wrong, isActive works on blocking functions too if you have a reference to the CoroutineScope (usually in a receiver). Can be used in tight loops.

[Dominaezzz]

Tomato/Tomato. 😛