java Android多线程SpeedTest存在性能问题

3 周，2 日 Questions & Answers 250

我最近开始做一个速度测试应用程序。方法很简单：

我实例化多个线程，所有线程都下载同一个不可压缩文件，然后计算平均下载速度

但我觉得我的表现有些问题。当我使用多个线程开始测试时，我在logCat中看到很多GC_CONCURRENT freed和WAIT_FOR_CONCURRENT_GC。我不明白那是从哪里来的

习惯性地，这些问题似乎出现在某些环境中，比如实例化太多的对象或巨大的对象，但我认为这里不是这样

以下是我的代码（简化-无速度计算）：

public class SpeedTest extends Activity{

    private final int NB_THREADS = 2;
    private long bytesIn;
    private long downloadTime;

    private List<Downloader> downloaders = new ArrayList<Downloader>();

    @Override
    protected void onCreate(Bundle savedInstanceState){

        super.onCreate(savedInstanceState);
        setContentView(R.layout.speed_test);

        bytesIn = 0;

        for (int i = 0; i < NB_THREADS; i++){
            downloaders.add(new Downloader());
            downloaders.get(i).executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, i);
        }
    }

    private synchronized void addBytes(){ bytesIn++; }

    private class Downloader extends AsyncTask<Integer, Void, Void>{

        @Override
        protected Void doInBackground(Integer... params){

            Log.d("eduine", "Downloader " + params[0] + " started");

            try{

                InputStream stream = new URL("http://test-de-vitesse.ariase.com/ariasetool/1mb_random.bin").openConnection().getInputStream();

                while((stream.skip(1)) != 0){
                    addBytes();
                }

                stream.close();

            }catch (MalformedURLException e){
                e.printStackTrace();
                Log.e("eduine", "malformed url : " + e.getMessage());
            }catch (IOException e){
                e.printStackTrace();
                Log.e("eduine", "io error : " + e.getMessage());
            }

            Log.d("eduine", "Downloader " + params[0] + " terminated");

            return null;
        }
    }
}

所以我想知道是否有人已经经历过这个问题，或者知道为什么会有这些性能问题，因为它扭曲了速度计算

提前谢谢

编辑：对不起，忘记发布日志了

02-12 14:18:40.945: D/eduine(15637): Downloader 0 started
02-12 14:18:40.955: D/eduine(15637): Downloader 1 started
02-12 14:18:41.355: D/dalvikvm(15637): GC_CONCURRENT freed 3102K, 33% free 7552K/11240K, paused 3ms+3ms, total 20ms
02-12 14:18:41.395: D/dalvikvm(15637): GC_CONCURRENT freed 1564K, 33% free 7533K/11240K, paused 3ms+3ms, total 18ms
02-12 14:18:41.465: D/dalvikvm(15637): GC_CONCURRENT freed 1657K, 33% free 7537K/11240K, paused 2ms+7ms, total 20ms
02-12 14:18:41.465: D/dalvikvm(15637): WAIT_FOR_CONCURRENT_GC blocked 8ms
02-12 14:18:41.485: D/dalvikvm(15637): GC_CONCURRENT freed 1657K, 33% free 7541K/11240K, paused 2ms+3ms, total 17ms
02-12 14:18:41.485: D/dalvikvm(15637): WAIT_FOR_CONCURRENT_GC blocked 10ms
02-12 14:18:41.505: D/dalvikvm(15637): GC_CONCURRENT freed 1669K, 33% free 7533K/11240K, paused 3ms+1ms, total 17ms
02-12 14:18:41.505: D/dalvikvm(15637): WAIT_FOR_CONCURRENT_GC blocked 10ms
02-12 14:18:41.525: D/dalvikvm(15637): GC_CONCURRENT freed 1609K, 33% free 7537K/11240K, paused 3ms+3ms, total 16ms
02-12 14:18:41.545: D/dalvikvm(15637): GC_CONCURRENT freed 1669K, 34% free 7529K/11240K, paused 3ms+2ms, total 16ms
02-12 14:18:41.545: D/dalvikvm(15637): WAIT_FOR_CONCURRENT_GC blocked 13ms

等等等等。。。直到

02-12 14:21:14.795: D/dalvikvm(16164): GC_CONCURRENT freed 1537K, 33% free 7533K/11240K, paused 3ms+2ms, total 16ms
02-12 14:21:14.815: D/dalvikvm(16164): GC_CONCURRENT freed 1537K, 33% free 7533K/11240K, paused 2ms+2ms, total 15ms
02-12 14:21:14.835: D/dalvikvm(16164): GC_CONCURRENT freed 1537K, 33% free 7533K/11240K, paused 2ms+3ms, total 16ms
02-12 14:21:14.845: D/eduine(16164): Downloader 0 terminated at 1392211274859
02-12 14:21:14.855: D/dalvikvm(16164): GC_CONCURRENT freed 1545K, 34% free 7529K/11240K, paused 3ms+3ms, total 17ms
02-12 14:21:14.915: D/eduine(16164): Downloader 1 terminated at 1392211274925

编辑：使用线程池时出现相同问题，代码如下

public class SpeedTest extends Activity{

    private final int NB_OF_THREADS = 8;
    private long bytesIn;
    private long start;

    ExecutorService executorService = new ThreadPoolExecutor(NB_OF_THREADS, NB_OF_THREADS, 1, TimeUnit.MINUTES, new ArrayBlockingQueue<Runnable>(NB_OF_THREADS, true), new ThreadPoolExecutor.CallerRunsPolicy());

    @Override
    protected void onCreate(Bundle savedInstanceState){

        super.onCreate(savedInstanceState);
        setContentView(R.layout.speed_test);

        bytesIn = 0;
        start = System.currentTimeMillis();
        for (int i = 0; i < NB_OF_THREADS; i++) executorService.submit(new Downloader(i));
    }

    private synchronized void addByte(){ bytesIn++; }

    private class Downloader implements Runnable{

        private int id;
        private InputStream stream;
        private long downloadTime;

        public Downloader(int _id){ id = _id; }

        @Override
        public void run(){

            Log.d("eduine", "Downloader " + id + " started at " + System.currentTimeMillis());

            try{

                HttpURLConnection connexion = (HttpURLConnection) new URL("http://test-de-vitesse.ariase.com/ariasetool/1mb_random.bin").openConnection();
                connexion.setUseCaches(false);
                stream = connexion.getInputStream();

                while((stream.skip(1)) != 0) addByte();

                stream.close();

                downloadTime = (System.currentTimeMillis() - start);
                downloadTime = downloadTime == 0 ? 1 : downloadTime;

            }catch (MalformedURLException e){
                e.printStackTrace();
                Log.e("eduine", "malformed url : " + e.getMessage());
            }catch (IOException e){
                e.printStackTrace();
                Log.e("eduine", "io error : " + e.getMessage());
            }

            Log.d("eduine", "Downloader " + id + " terminated at " + System.currentTimeMillis());
        }
    }
}

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