加载/清除大量数据时，std :: vector变得越来越慢

时间：2016-11-24 10:25:47

标签： c++ arrays windows memory vector

问题

我有一个非常复杂的图像处理应用程序，其中一个子模块需要将巨大的二进制位图加载到内存中。实际上高达96 GB（意味着888 888 x 888 888像素图像）。磁盘是2xSSD raid0，读/写速率约为1 GB / s。它将图像加载到带有字节的向量的智能指针的向量（每个元素表示位图中的一行）中（每个元素代表8个像素）。这里的奇怪问题是，在重复加载和清除向量之后（我看到内存实际上被填充并清除而没有内存泄漏），每次迭代似乎需要越来越长的时间。特别清除内存需要很长时间。

测试

我做了一些简单的测试应用程序来测试这个孤立的和不同的角度。 用原始指针替换智能指针给出了同样奇怪的行为。 然后我尝试使用原生数组而不是矢量，这就是诀窍。在100次迭代加载/清除之后24 GB时间在使用向量时急剧增加，而阵列实现在时间上是稳定的。下面是测试应用程序填充内存与24 GB垃圾而不是加载实际图像，具有相同的结果。在具有128 GB RAM的Windows 10 Pro上完成的测试，并使用Visual Studio 2013 Update 5构建。

此函数使用向量进行加载/清除：

void SimpleLoadAndClear_Vector(int width, int height) {
    time_t start_time, end_time;

    // Load memory
    time(&start_time);
    cout << "Loading image into memory...";
    auto width_bytes = width / 8;
    auto image = new vector<vector<unsigned char>*>(height);
    for (auto y = 0; y < height; y++) {
        (*image)[y] = new vector<unsigned char>(width_bytes);
        auto row_ptr = (*image)[y];
        for (auto b = 0; b < width_bytes; b++) {
            (*row_ptr)[b] = 0xFF;
        }
    }
    cout << "DONE: ";
    time(&end_time);
    auto mem_load = (int)difftime(end_time, start_time);
    cout << to_string(mem_load) << " sec" << endl;

    // Clear memory
    time(&start_time);
    cout << "Clearing memory...";
    for (auto y = 0; y < height; y++) {
        delete (*image)[y];
    }
    delete image;
    cout << "DONE: ";
    time(&end_time);
    auto mem_clear = (int)difftime(end_time, start_time);
    cout << to_string(mem_clear) + " sec" << endl;
}

此函数使用数组进行加载清除：

void SimpleLoadAndClear_Array(int width, int height) {
    time_t start_time, end_time;

    // Load memory
    time(&start_time);
    cout << "Loading image into memory...";

    auto width_bytes = width / 8;
    auto image = new unsigned char*[height];
    for (auto y = 0; y < height; y++) {
        image[y] = new unsigned char[width_bytes];
        auto row_ptr = image[y];
        for (auto b = 0; b < width_bytes; b++) {
            row_ptr[b] = 0xFF;
        }
    }
    cout << "DONE: ";
    time(&end_time);
    auto mem_load = (int)difftime(end_time, start_time);
    cout << to_string(mem_load) << " sec" << endl;

    // Clear memory
    time(&start_time);
    cout << "Clearing memory...";

    for (auto y = 0; y < height; y++) {
        delete[] image[y];
    }
    delete[] image;
    cout << "DONE: ";
    time(&end_time);
    auto mem_clear = (int)difftime(end_time, start_time);
    cout << to_string(mem_clear) + " sec" << endl;
}

这是调用上述加载/清除功能的主要功能：

void main()
{
    auto width = 455960;
    auto height = 453994;
    auto i_max = 50;
    for (auto i = 0; i < i_max; i++){
        SimpleLoadAndClear_Vector(width, height);
    }
}

矢量版本的测试输出在50次迭代后看起来如下（显然加载/清除时间越来越多）：

Loading image into memory...DONE: 19 sec
Clearing memory...DONE: 24 sec
Loading image into memory...DONE: 40 sec
Clearing memory...DONE: 20 sec
Loading image into memory...DONE: 27 sec
Clearing memory...DONE: 39 sec
Loading image into memory...DONE: 35 sec
Clearing memory...DONE: 24 sec
Loading image into memory...DONE: 27 sec
Clearing memory...DONE: 34 sec
Loading image into memory...DONE: 33 sec
Clearing memory...DONE: 29 sec
Loading image into memory...DONE: 27 sec
Clearing memory...DONE: 35 sec
Loading image into memory...DONE: 32 sec
Clearing memory...DONE: 33 sec
Loading image into memory...DONE: 28 sec
Clearing memory...DONE: 37 sec
Loading image into memory...DONE: 31 sec
Clearing memory...DONE: 35 sec
Loading image into memory...DONE: 30 sec
Clearing memory...DONE: 38 sec
Loading image into memory...DONE: 31 sec
Clearing memory...DONE: 38 sec
Loading image into memory...DONE: 31 sec
Clearing memory...DONE: 41 sec
Loading image into memory...DONE: 32 sec
Clearing memory...DONE: 40 sec
Loading image into memory...DONE: 33 sec
Clearing memory...DONE: 42 sec
Loading image into memory...DONE: 35 sec
Clearing memory...DONE: 43 sec
Loading image into memory...DONE: 34 sec
Clearing memory...DONE: 46 sec
Loading image into memory...DONE: 36 sec
Clearing memory...DONE: 47 sec
Loading image into memory...DONE: 35 sec
Clearing memory...DONE: 49 sec
Loading image into memory...DONE: 37 sec
Clearing memory...DONE: 50 sec
Loading image into memory...DONE: 37 sec
Clearing memory...DONE: 51 sec
Loading image into memory...DONE: 39 sec
Clearing memory...DONE: 51 sec
Loading image into memory...DONE: 39 sec
Clearing memory...DONE: 53 sec
Loading image into memory...DONE: 40 sec
Clearing memory...DONE: 52 sec
Loading image into memory...DONE: 40 sec
Clearing memory...DONE: 55 sec
Loading image into memory...DONE: 41 sec
Clearing memory...DONE: 56 sec
Loading image into memory...DONE: 41 sec
Clearing memory...DONE: 59 sec
Loading image into memory...DONE: 42 sec
Clearing memory...DONE: 59 sec
Loading image into memory...DONE: 42 sec
Clearing memory...DONE: 60 sec
Loading image into memory...DONE: 44 sec
Clearing memory...DONE: 60 sec
Loading image into memory...DONE: 44 sec
Clearing memory...DONE: 63 sec
Loading image into memory...DONE: 44 sec
Clearing memory...DONE: 63 sec
Loading image into memory...DONE: 45 sec
Clearing memory...DONE: 64 sec
Loading image into memory...DONE: 46 sec
Clearing memory...DONE: 65 sec
Loading image into memory...DONE: 45 sec
Clearing memory...DONE: 67 sec
Loading image into memory...DONE: 47 sec
Clearing memory...DONE: 69 sec
Loading image into memory...DONE: 47 sec
Clearing memory...DONE: 70 sec
Loading image into memory...DONE: 48 sec
Clearing memory...DONE: 72 sec
Loading image into memory...DONE: 48 sec
Clearing memory...DONE: 74 sec
Loading image into memory...DONE: 49 sec
Clearing memory...DONE: 74 sec
Loading image into memory...DONE: 50 sec
Clearing memory...DONE: 74 sec
Loading image into memory...DONE: 50 sec
Clearing memory...DONE: 76 sec
Loading image into memory...DONE: 51 sec
Clearing memory...DONE: 78 sec
Loading image into memory...DONE: 53 sec
Clearing memory...DONE: 78 sec
Loading image into memory...DONE: 53 sec
Clearing memory...DONE: 80 sec
Loading image into memory...DONE: 54 sec
Clearing memory...DONE: 80 sec
Loading image into memory...DONE: 54 sec
Clearing memory...DONE: 82 sec
Loading image into memory...DONE: 55 sec
Clearing memory...DONE: 91 sec
Loading image into memory...DONE: 56 sec
Clearing memory...DONE: 84 sec
Loading image into memory...DONE: 56 sec
Clearing memory...DONE: 88 sec

数组版本的测试输出在50次迭代后看起来如下（显然加载/清除时间稳定且不会增加越来越多）：

Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 17 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 17 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 17 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 25 sec
Loading image into memory...DONE: 27 sec
Clearing memory...DONE: 17 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 17 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 17 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 17 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 25 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 25 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 25 sec
Clearing memory...DONE: 19 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 25 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 25 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 25 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 25 sec
Loading image into memory...DONE: 25 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 25 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 25 sec
Clearing memory...DONE: 17 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 26 sec
Loading image into memory...DONE: 25 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 25 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 25 sec
Loading image into memory...DONE: 25 sec
Clearing memory...DONE: 19 sec
Loading image into memory...DONE: 18 sec
Clearing memory...DONE: 25 sec
Loading image into memory...DONE: 26 sec
Clearing memory...DONE: 18 sec

问题

  1. 这个Windows是否以错误的方式处理内存操作 处理巨大的std :: vectors？
  2. 是std :: vector只是表现糟糕 庞大的数据，按设计？
  3. 我完全错过了什么？
  4. 我应该使用其他明显的std容器（我需要通过不同线程的x和y索引访问图像数据）？
  5. 任何其他好的解释和建议的解决方案？

1 个答案:

答案 0 :(得分：2)

我做错了是我为图像中的每一行调用了矢量分配器（数千次）。当首先将整个事物分配为一个向量然后将不同的行映射到大向量中的正确位置时，问题就解决了。

感谢@PaulMcKenzie的答案，指出我正确的方向。

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