Alarm Manager not working at specific given time interval

Question

Hi I am using alarm Manager for specific time interval for 3 minutes and I started monitoring. It worked for sometimes and suddenly I noticed there is irregular time interval which is not correct! You can see in attached log where at "20-Jul-2016 12:22:03 pm" time varies! I connected the phone and turned off the screen and monitored! where for every 3 minutes, i hit the server and gets the response as 1. But at one time, it takes 5 minutes to hit the server! Why this strange issue happened?

Here is code.

 public void startAt3() {
    Intent alarmIntent = new Intent(ActivityTracking.this, AlarmReceiver.class);
    pendingIntent = PendingIntent.getBroadcast(ActivityTracking.this, 0, alarmIntent, 0);
    AlarmManager manager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
                        /* Set the alarm */
    Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(System.currentTimeMillis());
    /* Repeating on every 3 minute interval */
    manager.setInexactRepeating(AlarmManager.RTC_WAKEUP,
            calendar.getTimeInMillis(),
            180000L, pendingIntent);
    String mydate = java.text.DateFormat.getDateTimeInstance().format(Calendar.getInstance().getTime());
    Log.e("alarm",mydate);

}

AlarmReceiver:

   public class AlarmReceiver extends WakefulBroadcastReceiver    {//AlarmReceiver class
@Override
public void onReceive(Context context, Intent intent) {//onReceive method
    String mydate = java.text.DateFormat.getDateTimeInstance().format(Calendar.getInstance().getTime());
    Log.e("alarm",mydate);
    Intent service = new Intent(context, SimpleWakefulService.class);//intent to call another class
    // Start the service, keeping the device awake while it is launching.
    startWakefulService(context, service);//service started
}

SimpleWakefulService:

    public class SimpleWakefulService extends IntentService {
      public SimpleWakefulService() {
        super("SimpleWakefulService");//instantiates simpleWakefulService

    }
     @Override
     protected void onHandleIntent(Intent intent) {
        Log.e("simpleWakeful","simpleWakeful");
      serviceCall(this); //here is downloadTaskMethod called and getting response as 1.
  }

Answer 1

Don't use setInexactRepeating. This, as the name suggests, doesn't schedule the alarm to go off at an exact time.

You can use something like this:

public void scheduleSingleAlarm(Context context) {
    Intent intent = new Intent(context, NotificationReceiver.class);
    PendingIntent pendingUpdateIntent = PendingIntent.getBroadcast(context,
            SINGLE_ALARM_ID, intent, PendingIntent.FLAG_CANCEL_CURRENT);

    Calendar futureDate = Calendar.getInstance();
    futureDate.add(Calendar.MINUTE, 3);

    setSingleExactAlarm(futureDate.getTime().getTime(), pendingUpdateIntent);
}

@SuppressLint("NewApi")
private void setSingleExactAlarm(long time, PendingIntent pIntent) {
    if (android.os.Build.VERSION.SDK_INT >= 19) {
        mAlarmManager.setExact(AlarmManager.RTC_WAKEUP, time, pIntent);
    } else {
        mAlarmManager.set(AlarmManager.RTC_WAKEUP, time, pIntent);
    }
}

When you receive a call from the alarm, schedule another alarm to go off in another three minutes. I've blogged about this here