Question

I’m noticing a strange thing with Alarms on Android – they don’t always wake up the device at the correct intervals. For example, if I set an alarm to start a service every 5 minutes (using RTC_WAKEUP, or similar), everything works fine until the device goes to sleep – after that, the alarm may not fire for minutes, or close to an hour. It usually does fire eventually – and it always fires if I wake the device by pressing Menu. Using repeating alarms (vs. re-setting them each time) has the same effect.

So my question is, are alarms guaranteed to fire at proper intervals when the device is asleep? I understand that I shouldn’t expect millisecond or second precision, but tens of minutes?

Answer 1

I’ve never programmed on Android but I was kinda bored so I googled around and found this, which seems to be very related: http://groups.google.com/group/android-developers/browse_thread/thread/f0303a539de3a74a (you’ll need to sign in to your google account in order to read it)

I had another look at the AlarmManager
documentation and I noticed that it
only talks about using alarms to
broadcast events, not start services.
I changed things around to use a
BroadcastReceiver instead that
acquires the lock in its onReceive()
and stored the lock reference as a
static member of another class,
following the example of the
AlarmClock application:
https://android.googlesource.com/platform/packages/apps/AlarmClock

That seems to have worked. I guess
what was happening was that my service
starting alarms were being fired, but
the device was sometimes going back to
sleep before I could acquire the wake
lock. Apparently the only guarantee
that is made when an alarm is received
is that the onReceive will run to
completion.

I just thought I’d post this in case
anyone is ever searching for the same
problem.