java.util.ConcurrentModificationException: Unable to create service org.altbeacon.beacon.service.BeaconService

[rubnov]

I am using Altbeacon version 2.21.1 and seeing this crash in my Android app:

Fatal Exception: java.lang.RuntimeException: Unable to create service org.altbeacon.beacon.service.BeaconService: java.util.ConcurrentModificationException
       at android.app.ActivityThread.handleCreateService(ActivityThread.java:3768)
       at android.app.ActivityThread.access$1400(ActivityThread.java:237)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1801)
       at android.os.Handler.dispatchMessage(Handler.java:106)
       at android.os.Looper.loop(Looper.java:214)
       at android.app.ActivityThread.main(ActivityThread.java:7050)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)

Caused by java.util.ConcurrentModificationException:
       at java.util.ArrayList$Itr.next(ArrayList.java:860)
       at java.util.AbstractCollection.addAll(AbstractCollection.java:343)
       at org.altbeacon.beacon.service.ScanHelper.reloadParsers(ScanHelper.java:179)
       at org.altbeacon.beacon.service.BeaconService.onCreate(BeaconService.java:243)
       at android.app.ActivityThread.handleCreateService(ActivityThread.java:3756)
       at android.app.ActivityThread.access$1400(ActivityThread.java:237)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1801)
       at android.os.Handler.dispatchMessage(Handler.java:106)
       at android.os.Looper.loop(Looper.java:214)
       at android.app.ActivityThread.main(ActivityThread.java:7050)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)

Looking at the full stack trace, I can see this stack on another thread:

pool-25-thread-1:
       at android.os.BinderProxy.transactNative(Binder.java)
       at android.os.BinderProxy.transact(Binder.java:1145)
       at android.app.IActivityManager$Stub$Proxy.bindService(IActivityManager.java:4223)
       at android.app.ContextImpl.bindServiceCommon(ContextImpl.java:1761)
       at android.app.ContextImpl.bindService(ContextImpl.java:1701)
       at android.content.ContextWrapper.bindService(ContextWrapper.java:711)
       at org.altbeacon.beacon.BeaconManager$4.bindService(BeaconManager.java:2158)
       at org.altbeacon.beacon.BeaconManager.bindInternal(BeaconManager.java:622)
       at org.altbeacon.beacon.BeaconManager.autoBind(BeaconManager.java:2162)
       at org.altbeacon.beacon.BeaconManager.startMonitoring(BeaconManager.java:1415)
       at nl.hgrams.passenger.services.PSBluetoothService.addRegion(PSBluetoothService.java:1574)
       at nl.hgrams.passenger.services.PSBluetoothService.monitorAllBeaconRegions(PSBluetoothService.java:1764)
       at nl.hgrams.passenger.services.PSBluetoothService.initBeaconManager(PSBluetoothService.java:1277)
       at nl.hgrams.passenger.services.PSBluetoothService.lambda$startBeaconManager$11(PSBluetoothService.java:1254)
       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
       at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
       at java.lang.Thread.run(Thread.java:764)

This looks similar to this closed issue: #929

The issue is inconsistent and only occurred on a handful of devices, running Android 9-13.

My understanding of what's happening:

• My app launches and initializes BeaconManager.
• During initialization, the app starts monitoring a region (pool-25-thread-1). BeaconManager attempts to bind to BeaconService.
• However, at the same time BeaconService is being created. This results in the exception above.

Am I using the library incorrectly? Should I check BeaconService prior to calling startMonitoring?

Here is the relevant app code:

    /**
     * Initialize beacon manager to monitor beacon regions.
     */
    public void startBeaconManager() {
        BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        int result = BeaconTransmitter.checkTransmissionSupported(context);
        if (mBluetoothAdapter != null && result != BeaconTransmitter.NOT_SUPPORTED_BLE &&
                result != BeaconTransmitter.NOT_SUPPORTED_MIN_SDK) {
            if (Utils.hasPermissionBluetooth(context)) {
                ExecutorService executor = Executors.newSingleThreadExecutor();
                executor.execute(() -> initBeaconManager(context));
            }
        }
    }

    public void initBeaconManager(Context context) {
        if (beaconManager == null) {
            beaconManager = BeaconManager.getInstanceForApplication(context);
        }

            enableForegroundScanning();
            monitorAllBeaconRegions();
       ...
    }

    private void monitorAllBeaconRegions() {
        if (mIsAddingRegions) {
            return;
        }
        mIsAddingRegions = true;
        Realm realm = RealmManager.getInstance();
        BeaconSetting beaconSetting = realm.where(BeaconSetting.class).findFirst();
        if (beaconSetting != null) {
            addRegion(beaconSetting.getDefault_beacon_uuid()); 
        }
        ...
    }

    public void addRegion(String uuid) {
        if (uuid == null) { return; }
        if (beaconManager == null) { return; }
        Region region = new Region(uuid, Identifier.parse(uuid), null, null);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.UPSIDE_DOWN_CAKE &&
                !PSLocationService.userHasGrantedFineLocationPermission())
        {
            return;
        }
        beaconManager.startMonitoring(region);
    }

    public void enableForegroundScanning() {
        if (beaconManager != null) {
            if (beaconManager.getForegroundServiceNotification() != null) {
                return;
            } else if (beaconManager.isAnyConsumerBound()) {
                return;
            }
        }
        beaconManager.enableForegroundServiceScanning(
                NotificationCreator.getForegroundServiceNotification(PSApplicationClass.getInstance()),
                NotificationCreator.NOTIFICATION_ID_FOREGROUND_SERVICE);
        beaconManager.setForegroundBetweenScanPeriod(10000);
        beaconManager.setBackgroundBetweenScanPeriod(60000);
        beaconManager.setForegroundScanPeriod(5000);
        beaconManager.setBackgroundScanPeriod(4000);
    }

Thank you for your guidance.

[davidgyoung]

This is an unusual use of the library, which the library currently does not handle properly.

It looks like the app has 2+ threads all of which in parallel call startMonitoring or startRanging. This tries to start up a foreground scanning service, by using the relevant Android SDKs, which throw the exception you mention if two different threads do this at the same time.

The library should really fix this underlying exception in org.altbeacon.beacon.service.ScanHelper.reloadParsers(ScanHelper.java:179) but it may just cause another problem down the line.

I think the right solution for the library to this is to add an internal synchronize around BeaconConsumer.autoBind()

For your app, a quick fix might be to add some code to centralize where you start ranging or monitoring and wrap that in a synchronize block yourself, so two can't try to start up the scanning service at the same time.

[davidgyoung]

Similar issue here #1242, which is about the intent scan strategy instead of the foreground service strategy. Seems like a common solution could fix both.