Scanning for beacons using foreground service gives irregular scan intervals when device screen if off

[Kavish20]

I have configured the settings for my foreground service like below:

val settings = Settings(
scanStrategy = Settings.ForegroundServiceScanStrategy(
notification, 456
),
scanPeriods = Settings.ScanPeriods(10000L, 30000L, 10000L, 30000L),
longScanForcingEnabled = true
)
beaconManager.replaceSettings(settings)

It should wait for 30 seconds and then scan for 10 seconds in both foreground and background. Thus, one scan cycle will be of total 40 seconds.

The problem is when the app is killed and the device screen is off, the scan intervals are not regular, i.e they are not exactly 40 seconds. I have observed few cycles as low as 1 seconds and as high as 140 seconds.

Otherwise, when the device screen is on, the scan cycles are exactly at 40 seconds irrespective of the app is in the foreground or background.

The device I am using is Samsung M31 which runs on Android 12.

Is there any issue with the device hardware/software or some setting has to be configured in the library?

The library version is 2.21.1

[davidgyoung]

@Kavish20 please see the documentation section on "Restrictions on Foreground Service Start" here: https://altbeacon.github.io/android-beacon-library/foreground-service.html. You may be experiencing a case where the library is unable to start the foreground service do to operating system restrictions, and falls back to using the JobService strategy. You can read more about detection times for each strategy here: https://altbeacon.github.io/android-beacon-library/detection_times.html. You may wish to confirm if this is what is happening in your case by turning on library debug logging with BeaconManager.setDebug(true), then look at LogCat for when your app restarts after being killed to see if the foreground service is really starting or it is failing to do so and falling back go another strategy. Look for this log line "Foreground service blocked by ServiceStartNotAllowedException. Falling back to job scheduler": https://github.com/AltBeacon/android-beacon-library/blob/master/lib/src/main/java/org/altbeacon/beacon/BeaconManager.java#L614C52-L614C145

If you find the ForegroundService is running but the intervals are still irregular, I suggest turning on debug logging with BeaconManager.setDebug(true) and capturing some logs from the library's CycledLeScanner classs. This might tell us if the timers the library uses to schedule the scans are not firing as expected. https://github.com/AltBeacon/android-beacon-library/blob/master/lib/src/main/java/org/altbeacon/beacon/service/scanner/CycledLeScanner.java