Minimal android foreground service killed on high-

问题:

I'm trying to create an app that lets users log routes (locations/GPS). To ensure locations are logged even when the screen is off, I have created a foreground service for the location logging. I store the locations in a Room Database which is injected into my service using Dagger2.

However, this service is killed by Android which is, of course, not good. I could subscribe to low memory warnings but that doesn't solve the underlying problem of my service getting killed after ~30 minutes on a modern high-end phone running Android 8.0

I have created a minimal project with only a "Hello world" activity and the service: https://github.com/RandomStuffAndCode/AndroidForegroundService

The service is started in my Application class, and route logging is started through a Binder:

// Application
@Override
public void onCreate() {
    super.onCreate();
    mComponent = DaggerAppComponent.builder()
            .appModule(new AppModule(this))
            .build();

    Intent startBackgroundIntent = new Intent();
    startBackgroundIntent.setClass(this, LocationService.class);
    startService(startBackgroundIntent);
}

// Binding activity
bindService(new Intent(this, LocationService.class), mConnection, Context.BIND_AUTO_CREATE | Context.BIND_IMPORTANT);
// mConnection starts the route logging through `Binder` once connected. The binder calls startForeground()

I probably don't need the BIND_AUTO_CREATE flag, I've been testing different flags in an attempt to not get my service killed - no luck so far.

Using the profiler it does not seem like I have any memory leaks, memory usage is stable at ~35mb:

Using adb shell dumpsys activity processes > tmp.txt i can confirm that foregroundServices=true and my service is listed 8th in the LRU list:

Proc # 3: prcp F/S/FGS trm: 0 31592:com.example.foregroundserviceexample/u0a93 (fg-service)

It seems like it is not possible to create a foreground service that you can trust to not get killed. So what can we do? Well...

1. Put the service in a separate process, in an attempt to let Android kill the UI/Activities while leaving the service alone. Would probably help, but doesn't seem like a guarantee
2. Persist everything in the service in e.g. a Room database. Every variable, every custom class, every time any of the changes and then start the service with START_STICKY. This seems kind of wasteful and doesn't lead to very beautiful code, but it would probably work... somewhat. Depending on how long it takes for Android to re-create the service after killing it, a large portion of locations may be lost.

Is this really the current state of doing stuff in the background on Android? Isn't there a better way?

EDIT: Whitelisting the app for battery optimization (disabling it) does not stop my service from being killed

EDIT: Using Context.startForegroundService() to start the service does not improve the situation

EDIT: So this indeed only occurs on some devices, but it occurs consistently on them. I guess you have to make a choice of either not supporting a huge number of users or write really ugly code. Awesome.

回答1:

From the Processes and Application Lifecycle documentation:

3. [...] Services that have been running for a long time (such as 30 minutes or more) may be demoted in importance to allow their process to drop to the cached LRU list described next. This helps avoid situations where very long running services with memory leaks or other problems consume so much RAM that they prevent the system from making effective use of cached processes.
4. A cached process is one that is not currently needed, so the system is free to kill it as desired when memory is needed elsewhere. In a normally behaving system, these are the only processes involved in memory management: a well running system will have multiple cached processes always available (for more efficient switching between applications) and regularly kill the oldest ones as needed. [...]

There is your reason how some devices can chose to kill your service. First it is demoted to the cached LRU list and then the system is free to kill it.

Basically you answered the question yourself. The way to go is START_STICKY:

For started services, there are two additional major modes of operation they can decide to run in, depending on the value they return from onStartCommand(): START_STICKY is used for services that are explicitly started and stopped as needed, while START_NOT_STICKY or START_REDELIVER_INTENT are used for services that should only remain running while processing any commands sent to them. See the linked documentation for more detail on the semantics.

You can never be sure that your service is not killed at any time. E.g. memory pressure, low battery etc. See who-lives-and-who-dies.

As a general guideline you should do as little as possible in the background service, i.e. only do the location tracking and keep everything else in your foreground activity. Only the tracking should require very little configuration an can be loaded quickly. Also the smaller your service is the less likely it is to be killed. Your activity will be restored by the system in the state that is was before it went into background, as long as it is not killed as well. A "cold-start" of the foreground activity on the other hand should not be a problem.
I don't consider that as ugly, because this guarantees that the phone always provides the best experience to the user. This is the most important thing it has to do. That some devices close services after 30 minutes (possibly without user interaction) is unfortunate.

So, as you stated, you have to

Persist everything in the service in e.g. a Room database. Every variable, every custom class, every time any of them changes and then start the service with START_STICKY.

See creating a never ending service

Implicit question:

Depending on how long it takes for Android to re-create the service after killing it, a large portion of locations may be lost.

This usually takes only a really short time. Especially because you can use the Fused Location Provider Api for the location updates, which is an independent system service and very unlikely to be killed. So it mainly depends on the time you need to recreate the service in onStartCommand.

Also take note that from Android 8.0 onwards you need to use a forground service because of the background location limits.

---

Edit: As recently covered in the news: Some manufacturers may give you a hard time to keep your service running. The site https://dontkillmyapp.com/ keeps track of the manufacturers and possible mitigations for your device. Oneplus is currently (29.01.19) one of the worst offenders.

When releasing their 1+5 and 1+6 phones, OnePlus introduced one of the most severe background limits on the market to date, dwarfing even those performed by Xiaomi or Huawei. Not only did users need to enable extra settings to make their apps work properly, but those settings even get reset with firmware update so that apps break again and users are required to re-enable those settings on a regular basis.

Solution for users

Turn off System Settings > Apps > Gear Icon > Special Access > Battery Optimization.

sadly there is

No known solution on the developer end

回答2:

I suggest you use these: AlarmManager, PowerManager, WakeLock, Thread, WakefulBroadcastReceiver, Handler, Looper

I assume you already are using those "separate process" and other tweaks too.

So in your Application class:

MyApp.java:

import android.app.AlarmManager;
import android.app.Application;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.PowerManager;
import android.util.Log; 

public final class MyApp extends Application{

public static PendingIntent pendingIntent = null;
public static Thread                infiniteRunningThread;
public static PowerManager          pm;
public static PowerManager.WakeLock wl;


@Override
public void onCreate(){
    try{
        Thread.setDefaultUncaughtExceptionHandler(
                (thread, e)->restartApp(this, "MyApp uncaughtException:", e));
    }catch(SecurityException e){
        restartApp(this, "MyApp uncaughtException SecurityException", e);
        e.printStackTrace();
    }
    pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
    if(pm != null){
        wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "TAG");
        wl.acquire(10 * 60 * 1000L /*10 minutes*/);
    }

    infiniteRunningThread = new Thread();

    super.onCreate();
}

public static void restartApp(Context ctx, String callerName, Throwable e){
    Log.w("TAG", "restartApp called from " + callerName);
    wl.release();
    if(pendingIntent == null){
        pendingIntent =
                PendingIntent.getActivity(ctx, 0,
                                          new Intent(ctx, ActivityMain.class), 0);
    }
    AlarmManager mgr = (AlarmManager) ctx.getSystemService(Context.ALARM_SERVICE);
    if(mgr != null){
        mgr.set(AlarmManager.RTC_WAKEUP,
                System.currentTimeMillis() + 10, pendingIntent);
    }
    if(e != null){
        e.printStackTrace();
    }
    System.exit(2);
}
}

And then in your service:

ServiceTrackerTest.java:

import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.IBinder;
import android.os.Looper;
import android.os.PowerManager;
import android.support.v4.app.NotificationCompat;
import android.support.v4.content.WakefulBroadcastReceiver;

public class ServiceTrackerTest extends Service{

private static final int SERVICE_ID = 2018;
private static PowerManager.WakeLock wl;

@Override
public IBinder onBind(Intent intent){
    return null;
}

@Override
public void onCreate(){
    super.onCreate();
    try{
        Thread.setDefaultUncaughtExceptionHandler(
                (thread, e)->MyApp.restartApp(this,
                                              "called from ServiceTracker onCreate "
                                              + "uncaughtException:", e));
    }catch(SecurityException e){
        MyApp.restartApp(this,
                         "called from ServiceTracker onCreate uncaughtException "
                         + "SecurityException", e);
        e.printStackTrace();
    }
    PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
    if(pm != null){
        wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "TAG");
        wl.acquire(10 * 60 * 1000L /*10 minutes*/);
    }


    Handler h = new Handler();
    h.postDelayed(()->{

        MyApp.infiniteRunningThread = new Thread(()->{
            try{
                Thread.setDefaultUncaughtExceptionHandler(
                        (thread, e)->MyApp.restartApp(this,
                                                      "called from ServiceTracker onCreate "
                                                      + "uncaughtException "
                                                      + "infiniteRunningThread:", e));
            }catch(SecurityException e){
                MyApp.restartApp(this,
                                 "called from ServiceTracker onCreate uncaughtException "
                                 + "SecurityException "
                                 + "infiniteRunningThread", e);
                e.printStackTrace();
            }

            Looper.prepare();
            infiniteRunning();
            Looper.loop();
        });
        MyApp.infiniteRunningThread.start();
    }, 5000);
}

@Override
public void onDestroy(){
    wl.release();
    MyApp.restartApp(this, "ServiceTracker onDestroy", null);
}

@SuppressWarnings("deprecation")
@Override
public int onStartCommand(Intent intent, int flags, int startId){
    if(intent != null){
        try{
            WakefulBroadcastReceiver.completeWakefulIntent(intent);
        }catch(Exception e){
            e.printStackTrace();
        }
    }
    startForeground(SERVICE_ID, getNotificationBuilder().build());
    return START_STICKY;
}


private void infiniteRunning(){
    //do your stuff here
    Handler h = new Handler();
    h.postDelayed(this::infiniteRunning, 300000);//5 minutes interval
}

@SuppressWarnings("deprecation")
private NotificationCompat.Builder getNotificationBuilder(){
    return new NotificationCompat.Builder(this)
                   .setContentIntent(MyApp.pendingIntent)
                   .setContentText(getString(R.string.notification_text))
                   .setContentTitle(getString(R.string.app_name))
                   .setLargeIcon(BitmapFactory.decodeResource(getResources(),
                                                              R.drawable.ic_launcher))
                   .setSmallIcon(R.drawable.ic_stat_tracking_service);
}

}

Ignore "Deprecation" and stuff, use them when you have no choice. I think the code is clear and doesn't need to be explained. It's just about workaround suggestions and solutions.