c - 如何使用openmp转换jpg2dicom？

Question

我需要将数百张 jpg 图像转换为 dicom。我有一个 Web 应用程序，该应用程序最初是用 Node.js 制作的，但速度非常慢。我想用 C 语言并使用 openmp 来并行化以下代码:

int main(){
    DIR *dir;
    struct dirent *arq; 
    dir = opendir("./jpg");
    char cmd1[255] = "./dcm4che-2.0.23/bin/jpg2dcm -c dcm4che-2.0.23/etc/jpg2dcm/jpg2dcm.cfg jpg/";
    char cmd_aux[255] = "./dcm4che-2.0.23/bin/jpg2dcm -c dcm4che-2.0.23/etc/jpg2dcm/jpg2dcm.cfg jpg/"; 
    char buf[255];
    char nomeArq[255];
    int i;
    //Stretch in which I use openmp 
    while ((arq = readdir(dir)) != NULL){
        strncpy(nomeArq, arq->d_name, 255);
        if(nomeArq[0] != '.'){
           sprintf(buf, " dcm/imagem-%d.dcm", i); 
           strcat(cmd1, nomeArq); // cmd1 + nomeArquivo
           strcat(cmd1, buf); 
           system(cmd1); 
           strncpy(cmd1, cmd_aux, 255);
     }
      i++;
    }
    closedir(dir);
    return 0;
}

我怎么知道这段代码是 I/O 限制的，我想问一下 openmp 是否真的无法获得任何加速。如果可能的话，如何在使用 openmp 时并行化这个循环。如果我说得不太清楚，抱歉!我还在学英语!

Answer 1

Bash 解决方案

首先，如果您考虑现有工具，您的任务会更容易:

• GNU Parallel
• xargs使用多进程参数

示例为 xargs (从 bash 命令提示符处):

ls ./jpg | xargs -P 0 -i ./dcm4che-2.0.23/bin/jpg2dcm -c dcm4che-2.0.23/etc/jpg2dcm/jpg2dcm.cfg jpg/{} dcm/{}.dcm

OpenMP

使用 for 循环更容易，您可以开始将文件列表放入数组中( Stackoverflow code 了解如何操作)。

// put your code for reading he files list into an array //

int main() {
    char **files;
    const size_t count = file_list("./jpg", &files);

    #pragma omp parallel for
    for(size_t i=0;i<count;++i) {
        if(files[i][0] == '.' ) { continue; } // 'skip' directory entry, maybe you should implement some better check ( extension, or even checking if it is a file at all)
        // keep the buffer local to the loop
        char *buf = malloc(1024);
        // already calling sprintf, use it for building the whole command line, and avoid the strncpy & strcat
        sprintf(buf, "./dcm4che-2.0.23/bin/jpg2dcm -c dcm4che-2.0.23/etc/jpg2dcm/jpg2dcm.cfg jpg/%s dcm/imagem-%zu.dcm",files[i],i);
        system(buf);
        free(buf); // cleanup
    }
    return EXIT_SUCCESS;
}