Android AlarmManager is sometimes late

Question

I have an application that needs to run the background service regularly, and I use AlarmManager to achieve this behavior. To shorten a long story, it is set to run twice per minute (every 30 seconds), and to complete (basically sleep) takes about 20 seconds.

I use several Android devices for testing (Galaxy SII with 4.1.2, Nexus 4 with 4.2.2 and later with CyanogenMOD 10.1.2 and Nexus 7 with 4.2.2), and they all behave sequentially when connected to USB and debugger

As soon as I disconnect the device and leave it on the table, I noticed that the SOMETIMES service will skip one interval. Looking very carefully at the magazine, I see that the service is sometimes delayed for a certain period of time. If it should work in xx: 05 and xx: 35, I noticed that it starts with xx: 45 (10 seconds later than it should).

The very first thing a service does is to get a partial watchdog lock to ensure that the processor does not fall asleep while it is running - this lock lock is not released until it completely does what it needs to do.

My first thought was that the reason was some kind of resource sharing that caused the behavior (there are other processes running with the application), but the service does not even start, it does not even get a tracking lock until 10 seconds later.

It is worth noting that this behavior is most pronounced on Nexus 4, where up to 30% of the data is missing, and on Galaxy SII and Nexus 7 (about ~ 2%), it is significantly less, but this is still worrying, because the inexplicable behavior.

Answer 1

You did not indicate which alarm you are using, but given your complaints, I assume it is an _WAKEUP alarm. If so, the only guarantee we have is, if we use the PendingIntent broadcast, Android will support waking the device during an onReceive() call. Using the PendingIntent service, as you do, is unreliable, as the device may fall asleep before the service starts and may receive WakeLock .

Therefore, a more reliable pattern for the _WAKEUP is to use the _WAKEUP broadcast, enter BroadcastReceiver acquire() WakeLock , then call startService() to transfer control to your service, your service will do its job, then release WakeLock .

I have this template wrapped in my WakefulIntentService component .