Leak resulting from RxBleClient.scanBleDevices()

I’ve been pulling my hair out trying to debug a leak in my app when using RxBleClient.scanBleDevices(). My subscribe onNext lambda holds a reference to the Activity, however I am unsubscribing when the Activity is destroyed, so I shouldn’t be leaking. The leak’s GC root is a thread, which references com.polidea.rxandroidble.internal.radio.FIFORunnableEntry.emitter.

Maybe I’m just missing something here? In that case, any insight is greatly appreciated.

I’ve created an example that demonstrates the issue:

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

import com.google.common.base.Strings;
import com.polidea.rxandroidble.RxBleClient;
import com.polidea.rxandroidble.scan.ScanSettings;

import com.example.R;
import com.example.MyApplication;
import rx.Observable;
import rx.Subscription;
import timber.log.Timber;

public class DebugLeakActivity extends AppCompatActivity {

    RxBleClient bleClient;
    Subscription subscription = null;
    String someActivityField;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_debug_leak);

        // in my app, RxBleClient is provided by dependency injection and has the lifetime of the app.
        // simulating here.
        bleClient = ((MyApplication)getApplication()).bleClient;

    }

    @Override
    protected void onStart() {
        super.onStart();

        subscription = scan()
                .subscribe(
                        // reference a field in the activity to create a reference to the Activity from the lambda
                        deviceString -> someActivityField = deviceString,
                        throwable -> Timber.e(throwable));
    }

    @Override
    protected void onDestroy() {

        if (subscription != null) {
            subscription.unsubscribe();
            subscription = null;
        }
        super.onDestroy();
    }

    public Observable<String> scan() {
        ScanSettings scanSettings = new ScanSettings.Builder()
                .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
                .build();

        return bleClient.scanBleDevices(scanSettings)
                .doOnUnsubscribe(() -> Timber.d("scanBleDevices() unsubscribed"))
                .distinct()
                .doOnNext(scanResult -> Timber.d(String.format("Found BLE device: %s, %s", scanResult.getBleDevice().getMacAddress(), Strings.nullToEmpty(scanResult.getBleDevice().getName()))))
                .map(rxBleScanResult -> rxBleScanResult.toString());
    }
}

Here is the reference chain from LeakCanary:

In com.example:0.20.0-SNAPSHOT:200000.
* com.example.presentation.DebugLeakActivity has leaked:
* GC ROOT thread java.lang.Thread.<Java Local> (named 'Thread-8')
* references com.polidea.rxandroidble.internal.radio.FIFORunnableEntry.emitter
* references rx.internal.operators.OnSubscribeCreate$NoneEmitter.actual
* references rx.internal.operators.OperatorUnsubscribeOn$1.val$subscriber (anonymous subclass of rx.Subscriber)
* references rx.internal.operators.OnSubscribeMap$MapSubscriber.actual
* references rx.internal.operators.OperatorMerge$InnerSubscriber.parent
* references rx.internal.operators.OperatorMerge$MergeSubscriber.child
* references rx.observers.Subscribers$5.val$subscriber (anonymous subclass of rx.Subscriber)
* references rx.observers.Subscribers$5.val$subscriber (anonymous subclass of rx.Subscriber)
* references rx.observers.Subscribers$5.val$subscriber (anonymous subclass of rx.Subscriber)
* references rx.internal.operators.OperatorDistinct$1.val$child (anonymous subclass of rx.Subscriber)
* references rx.internal.operators.OnSubscribeDoOnEach$DoOnEachSubscriber.subscriber
* references rx.internal.operators.OnSubscribeMap$MapSubscriber.actual
* references rx.observers.SafeSubscriber.actual
* references rx.internal.util.ActionSubscriber.onNext
* references com.example.presentation.DebugLeakActivity$$Lambda$1.arg$1 (anonymous implementation of rx.functions.Action1)
* leaks com.example.presentation.DebugLeakActivity instance

I’ve attached the full LeakCanary details for more information: In 2.txt

[streetsofboston]

Looking at this code snippet:

    @Override
    protected void onStart() {
        super.onStart();

        subscription = scan()
                .subscribe(
                        // reference a field in the activity to create a reference to the Activity from the lambda
                        deviceString -> someActivityField = deviceString,
                        throwable -> Timber.e(throwable));
    }

    @Override
    protected void onDestroy() {

        if (subscription != null) {
            subscription.unsubscribe();
            subscription = null;
        }
        super.onDestroy();
    }

The onStart can be called multiple times before the onDestroy is finally called.

Instead of unsubscribing in the onDestroy, override the onStop instead and unsubscribe there.

[dariuszseweryn]

I think that @streetsofboston comment may pinpoint the cause of the observed leak. Closing for now. If new information will be available—feel free to reopen.