为什么我的流复制过程性能稳定下降

Question

此代码在复制大文件时运行速度越来越慢。我做错了什么吗？

    InputStream ms2 = new BufferedInputStream(new FileInputStream("/home/fedd/Videos/homevid.mp4"));
    OutputStream fos2 = new BufferedOutputStream(new FileOutputStream("testfile2.mp4", true));

    try {
        int byt;
        int i = 0;
        long time = System.currentTimeMillis();
        while ((byt = ms2.read()) != -1) {
            fos2.write(byt);
            i++;
            if (i > 100000) {
                i = 0;
                long took = System.currentTimeMillis() - time;
                System.out.println("100000 bytes took " + took + " milliseconds which means " + (100000000 / took) + " bytes per second");
            }
        }
        fos2.close();
        ms2.close();
    } catch (Exception e) {
        throw new RuntimeException(e);
    }

我的Java是：

openjdk 10.0.2 2018-07-17 OpenJDK Runtime Environment (build 10.0.2+13-Ubuntu-1ubuntu0.18.04.4)

OpenJDK 64-Bit Server VM (build 10.0.2+13-Ubuntu-1ubuntu0.18.04.4, mixed mode)

Answer 1

你的表现下降是因为你的计算有误。对于第二个块，您是根据第二个块的大小计算每秒的字节数，但从两个块的时间计算。尝试在 long took = ...

之后添加 time = System.currentTimeMillis();

Answer 2

您需要在每次比较后重置您的基地 'time'。试试这个：

if (i > 100000) {
    i = 0;
    long took = System.currentTimeMillis() - time;
    time = System.currentTimeMillis();
    System.out.println("100000 bytes took " + took + " milliseconds which means " + (100000000 / took) + " bytes per second");
}

为什么我的流复制过程性能稳定下降

Why does my stream copying procedure steadily degrades in performance

java

java-io