AlarmManager not starting up

    Intent myIntent = new Intent(taskiller.this, taskiller.class);
    pendingIn开发者_如何学JAVAtent = PendingIntent.getService(taskiller.this, 0, myIntent, 0);

    AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
    Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(System.currentTimeMillis());
    //Set taskiller at 20secs
    calendar.add(Calendar.SECOND, 20);
    alarmManager.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis() , pendingIntent);
    Log.i("Securitas", "Set alarm to be triggered");

I want my service to restart itself after a certain time interval but it doesnt seem to happen. Can anybody please advice?