Possible concurrency issue in scan

[jihyeon]

If we unsubscribe the scan right after subscribe (e.g., repeated activity pause/resume, or timeout/retryWhen), scanning started after stop request. We have to kill the app to stop it.

Here's a brief logcat output for the scenario.

// Subscribe and scan start

D/AObserver(31609): start scan
D/RxBle#Radio(31609):   QUEUED RxBleRadioOperationScan(7307165)
D/RxBle#Radio(31609):  STARTED RxBleRadioOperationScan(7307165)

// RxBleRadioImpl thread is running but startLeScan() is not called yet
// now we pause the activity and unsubscribe

V/AActivity(31609): ⇢ onPause()
D/AObserver(31609): Frodo => [@Observable#observe -> @SubscribeOn -> main :: @ObserveOn -> main]
D/AObserver(31609): Frodo => [@Observable#observe -> onUnsubscribe()]
D/BluetoothAdapter(31609): stopLeScan()
D/BluetoothAdapter(31609): scan not started yet    <------------------!!!!!!!!!!!
V/AActivity(31609): ⇠ onPause()

// RxBleRadioImpl thread is still running in the background
// and start the scan

D/BluetoothAdapter(31609): startLeScan(): null
D/BtGatt.GattService(13895): registerClient() - UUID=f17ebcd4-...
D/BtGatt.GattService(13895): onClientRegistered() - UUID=f17ebcd4-..., clientIf=5
D/BluetoothLeScanner(31609): onClientRegistered() - status=0 clientIf=5
D/BtGatt.GattService(13895): start scan with filters
D/BtGatt.ScanManager(13895): handling starting scan
D/BtGatt.ScanManager(13895): configureRegularScanParams() - queue=1
D/BtGatt.ScanManager(13895): configureRegularScanParams() - ScanSetting Scan mode=2 ...
D/RxBle#Radio(31609): FINISHED RxBleRadioOperationScan(7307165)
D/BluetoothLeScanner(31609): onScanResult() - ScanResult{mDevice= ...}
D/BluetoothLeScanner(31609): onScanResult() - ScanResult{mDevice= ...}
D/BluetoothLeScanner(31609): onScanResult() - ScanResult{mDevice= ...}
......

// there's no way to stop the scan. we have to kill the app

[dariuszseweryn]

Should be fixed in 4d92c4f