AlarmManager无法启动

Question

    Intent myIntent = new Intent(taskiller.this, taskiller.class);
    pendingIntent = 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");

我希望我的服务在一段时间间隔后重新启动，但似乎不会发生。 有人可以建议吗？