setExactAndAllowWhileIdle - is not exact as of developer reference

Solution 1:

So how can I achieve an exact alarm with AlarmManager in 6.0?

You are welcome to try setAlarmClock(), as AFAIK it is unaffected by Doze mode. Otherwise, AlarmManager is not a viable option for you. Even having your app on the battery optimization whitelist will not help, as AlarmManager behavior does not change based on the whitelist.

You are welcome to use GCM, as a high-priority message should give you an opportunity to alert the user. This, of course, requires network connectivity.

The only offline solution that I am aware of — and that I am presently testing — is to have the user add your app to the battery optimization whitelist, then use a foreground service (to try to keep your process around), a ScheduledExecutorService (for the timing), and a partial WakeLock (to keep the CPU on). This will be fairly devastating to the user's battery.

Solution 2:

Using setExactAndAllowWhileIdle() for a one-time alarm will fire exactly on the given time even in Doze idle mode. So this probably is the way to go.

Problems start, if you want to repeat the alarm at a rate of < 15 min (or set any other at a time < 15 min away from the last one), as this will not work in Doze idle mode, where such alarms are forced to the next 15 min or are executed when idle maintenance starts, which happens for about ten minutes first after 1 hour, then after another 2 hours, then after another 4 hours and so on.

- EDIT -

As of today Nov 17, Dianne Hackborn writes in this Post's comments: "For what it's worth, the minimum time between while idle alarms will be changing to 9 minutes at some point relatively soon (even on devices running the current Marshmallow builds)."

This doesn't change anything fundamentally though.

Solution 3:

Here are my discussion with Ian Lake on Google+!

setExactAndAllowWhileIdle() is exact and should work. The 15 minutes time frame is wrong in the java doc.

Solution 4:

I have found that so far the best option is to use a SyncAdapter that extends AbstractThreadedSyncAdapter. I schedule it to automatically keep running my code at the required interval:

ContentResolver.setSyncAutomatically(account, AUTHORITY, true);
ContentResolver.addPeriodicSync(account, AUTHORITY, settingsBundle, syncInterval);