Calling a suspend function from a function block i...

# coroutines

[Miguel Vargas]

Calling a suspend function from a function block in a suspend function doesn’t work

private suspend fun outerSuspend() {
    timer(period = 10) {
        innerSuspend() // Error: Suspend functions can be only called within coroutine body
    }
}

It works if I create a new CoroutineScope inside the function block

private suspend fun outerSuspend() {
    timer(period = 10) {
        CoroutineScope(<http://Dispatchers.IO|Dispatchers.IO>).launch {
            innerSuspend()
        }
    }
}

Is there a way to use the outer scope in the inner block?

[octylFractal]

in order to do that you need to have timer be inline or suspend itself

[streetsofboston]

And if that is not possible (timer being inline/suspend), you can do this:

private suspend fun outerSuspend() = coroutineScope {
    timer(period = 10) {
        launch { innerSuspend() }
    }
}

Because creating a new CoroutineScope, like in your original example’s solution, breaks cancellation/structured-concurrency.

[octylFractal]

hmm, but that does not actually gate the code in the timer

[octylFractal]

you would have to explicitly runBlocking it to do that (or runInterruptible in more recent versions)

[streetsofboston]

Yup. But I didn’t think that gating it was needed

[gildor]

Just curious what timer does. It looks that it easier to reimplement it with coroutines than try to use non-suspend version of it, also it would make it properly cancellable

[streetsofboston]

True. A

while (isActive) { 
    innerSuspend()
    delay(periodInMillis)
}

is a straightforward solution.

[gildor]

yeah, if it repeat just use delay before or after innerSuspend, and remove while if you don’t need repeat and you just want wait

[julian]

@octylFractal You used the term "gate". What does it mean?

[octylFractal]

basically that it will "escape" outside a normal sequential execution flow, i.e. if the timer function was intended to cancel / interrupt / measure the inner block, it would not do so properly because launch immediately returns in this case

[octylFractal]

"gate" is a bit metaphorical in this case, I'm not really sure I could explain it well

[julian]

I think I get it. Thanks @octylFractal!