iOS why system kills the app using location in background

Question

I have an app that uses the location updates when it is in the foreground as well as in the background. Using the CoreLocation framework, I have implemented the app so that location updates are sent to the server after every 5 minutes, using this code as a reference.

This works fine in foreground, but when the app goes to the background, it is getting killed by the OS after 30 minutes to an hour. I want the app to get updates for at least 8 hours, even in the background.

Also, the app is using the about 10% of the battery per hour. Is this related to the app being killed in the background? If so, then how can I resolve the battery problem? Otherwise, can anyone tell me what the issue is?

Below is the crash log for the device:

Exception Type:  00000020
Exception Codes: 0x000000008badf00d
Exception Note:  SIMULATED (this is NOT a crash)
Highlighted by Thread:  2

Application Specific Information:
<BKNewProcess: 0x17e74840; com.app.app; pid: 560; hostpid: -1> has active assertions beyond permitted time: 
{(
<BKProcessAssertion: 0x17d78740> id: 560-C9E81E97-90D9-4F95-871E-3DC53372F302 name: Called by UIKit, from <redacted> process: <BKNewProcess: 0x17e74840; com.app.example; pid: 560; hostpid: -1> permittedBackgroundDuration: 180.000000 reason: finishTask owner pid:560 preventSuspend  preventIdleSleep  preventSuspendOnSleep ,
<BKProcessAssertion: 0x17e6a870> id: 560-BD7B29FC-DABC-42FF-AF17-B277BDB1C59D name: Called by UIKit, from <redacted> process: <BKNewProcess: 0x17e74840; com.app.example; pid: 560; hostpid: -1> permittedBackgroundDuration: 180.000000 reason: finishTask owner pid:560 preventSuspend  preventIdleSleep  preventSuspendOnSleep 
)}

For the background task I use the following function:

func backgroundTask(){
    var application=UIApplication.sharedApplication()
    var background_task: UIBackgroundTaskIdentifier?
    background_task = application.beginBackgroundTaskWithExpirationHandler({() -> Void in
        application.endBackgroundTask(background_task!)
        background_task = UIBackgroundTaskInvalid
    })
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {() -> Void in
        //run the app without startUpdatingLocation. backgroundTimeRemaining decremented from 600.00
        self.locationManager.startUpdatingLocation()
        while (true) {
            //backgroundTimeRemaining time does not go down.
            print("Background time Remaining: \(UIApplication.sharedApplication().backgroundTimeRemaining)")
            NSThread.sleepForTimeInterval(1)

            break
            //wait for 1 sec
        }
        application.endBackgroundTask(background_task!)
        background_task = UIBackgroundTaskInvalid
    })

}

Answer 1

When your app enters in background state switch to significant location updates and your app will receive location update continuously. you can call startMonitoringSignificantLocationChanges on CLLocationManger's object i think. And you not need to establish background task also i think.

Check the Apple Documentation, It states,

If you start this service and your app is subsequently terminated, the system automatically relaunches the app into the background if a new event arrives. In such a case, the options dictionary passed to the application:willFinishLaunchingWithOptions: and application:didFinishLaunchingWithOptions: methods of your app delegate contains the key UIApplicationLaunchOptionsLocationKey to indicate that your app was launched because of a location event. Upon relaunch, you must still configure a location manager object and call this method to continue receiving location events. When you restart location services, the current event is delivered to your delegate immediately. In addition, the location property of your location manager object is populated with the most recent location object even before you start location services

So, it will solve your problem i think and it will solve issue of battery also.

Second thing (for battery consumption), You should not set DesiredAccuracy to kCLLocationAccuracyBest when want to update location in background for long time. You can set kCLLocationAccuracyThreeKilometers as DesiredAccuracy and you can set setDistanceFilter to very big digit like 99999 when enter in background.

You can refer this so post and this so post.

Hope this will help :)

Answer 2

Do you have any crash log.If application not terminated by exception of some hidden bug you should suspicious of memory pressure.I think this article will lead you to find reason of sudden termination

https://www.raywenderlich.com/23704/demystifying-ios-application-crash-logs