Hello, I'm working on converting a callback from a...

# coroutines

[alexandre mommers]

Hello, I'm working on converting a callback from a C library into a suspend function. I'm considering using :

suspend fun myFun() {
    val atomicLong = AtomicReference<Long?>(null)

    externalFunctionWithCallback { value ->
        atomicLong.set(value)
    }

    while (atomicLong.get() == null) {
        yield()
    }

    return atomicLong.get()
}

Or may be this one

suspend fun myFun() {
    val atomicLong = AtomicReference<Long?>(null)

    externalFunctionWithCallback { value ->
        atomicLong.set(value)
    }

    while (atomicLong.get() == null) {
        delay(1000)
    }

    return atomicLong.get()
}

What do you think? The goal would be to let other coroutine run while I'm waiting something

[Sam]

Did you consider using suspendCoroutine (or suspendCancellableCoroutine)?

[Joffrey]

Ah, you beat me to it 😅

[Sam]

suspend fun myFun() = suspendCoroutine<Long> { cont ->
  externalFunctionWithCallback { value ->
    cont.resume(value)
  }
}

[alexandre mommers]

Thanks I will check that !

[Joffrey]

And if the external function somehow allows cancellation, you could use the suspendCancellableCoroutine variant to make it cooperate with coroutines cancellation:

suspend fun myFun() = suspendCancellableCoroutine<Long> { cont ->

  // you could also put this after the external call depending on the API to cancel
  cont.invokeOnCancellation { ...cancel/stop/cleanup code here... }

  externalFunctionWithCallback { value ->
    cont.resume(value)
  }
}

[Joffrey]

Note that you could also use this variant if the external function does NOT support cancellation (thus without the invokeOnCancellation call), but if you do this, you will technically leak the non-cancelled external function call, which is probably a bad idea