JobIntentService不能像IntentService一样在完成后删除线程

Question

我有来自官方文档的JobIntentService：

public class SimpleJobIntentService extends JobIntentService {

    static final int JOB_ID = 1000;

    static void enqueueWork(Context context, Intent work) {
        enqueueWork(context, SimpleJobIntentService.class, JOB_ID, work);
    }

    @Override
    protected void onHandleWork(Intent intent) {
        // We have received work to do.  The system or framework is already
        // holding a wake lock for us at this point, so we can just go.
        Log.i("SimpleJobIntentService", "Executing work: " + intent);
        String label = intent.getStringExtra("label");
        if (label == null) {
            label = intent.toString();
        }
        toast("Executing: " + label);
        for (int i = 0; i < 5; i++) {
            Log.i("SimpleJobIntentService", "Running service " + (i + 1)
                    + "/5 @ " + SystemClock.elapsedRealtime());
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
            }
        }
        Log.i("SimpleJobIntentService", "Completed service @ " + SystemClock.elapsedRealtime());
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        toast("All work complete");
    }

    final Handler mHandler = new Handler();

    // Helper for showing tests
    void toast(final CharSequence text) {
        mHandler.post(new Runnable() {
            @Override public void run() {
                Toast.makeText(SimpleJobIntentService.this, text, Toast.LENGTH_SHORT).show();
            }
        });
    }
}

在运行此服务之前，在致电Thread.activeCount()之后，我得到了 数字33。结束第一次运行的服务后，我得到了34，接下来是35，依此类推。
为什么呢有人可以解释我吗？结束后如何杀死该线程？这是JobIntentService的正常行为吗？ IntentService可以正常工作，总是在结束后杀死线程。

我使用以下代码从片段启动此服务：

Intent intent = new Intent(getActivity(), SimpleJobIntentService.class);
SimpleJobIntentService.enqueueWork(getActivity(), intent);

无论如何，如果我这样启动服务：

getActivity().startService(new Intent(getActivity(), SimpleJobIntentService.class));

JobIntentService也无法删除线程