What will happen inside

suspendCancellableCoroutine

if a callback causes calling

continuation.resume()

twice? E.g.

suspendCancellableCoroutine { continuation ->
            bleManager.startScan(
                onDeviceAppeared = { device ->
                        continuation.resume(Unit.right())
                    }
                },
                onScanError = {
                    continuation.resume(it.left())
                },
             )
        }

If I get a second

onDeviceAppeared

callback will the coroutine try to resume again?

It'll throw an exception: Continuations can only be resumed once.

Ok, so the correct solution is to remove the callback before resuming?

Yup, or guard it.

Oh yes, good point. Thank you!

However, if onDeviceAppeared can occur more than once, you may want to consider using a Flow (callbackFlow { ... }) instead.

I just want to finish the scan after first device

Still, maybe a Flow could be good to use as the one that produces the scanned devices and then call

devicesFlow.first()

on it to get the first one.

Yes, that's also a good idea

Then you can filter the flow, combine, etc

Sorry, I haven't made myself clear. I meant rather the stopping of the BLE scan

Ah... yup.

Also Flow would guarantee the

resume

cannot be called twice

You mean 'suspend' would guarantee that? A Flow's

emit

can be called many times.

1. In case of

suspendCancellableCoroutine

I filter for the specific device inside of the callback. That means, if

onDeviceAppeared

will be called twice for the same device, I would try to

resume

twice. 2. In case of a

callbackFlow

I would just emit the same device twice -> no problem, as the collection on consumer side probably already finished anyway (because we stopped collecting when we got the desired device).

Yup; and you can filter (eg filter on name) inside the callbackFlow, like you would in a suspendCancellableCoroutine, but also later in a

.filter

operator.

Yes, that's also much nicer.

You're welcome 🙂