Question

我正在尝试多线程一个程序，它从文件中取出单词然后散列这些并写入另一个程序。

如果我在没有多线程的情况下完成它的速度非常快，那么它只能使用15-20％的CPU并且具有类似于300.000line / s的速度

但是当我尝试使用多线程时，它只会减速并开始仅以17000行/秒的速度散列，你能帮助我吗？

由于

#include <iostream>     // std::cout, std::streambuf, std::streamsize
#include <fstream>      // std::ifstream
#include <string>
#include <thread>
#include "md5.h"

using namespace std;

static const int num_threads = 10;

void call_from_thread(int tid) {
    cout << "Launched by thread " << tid << std::endl;
    int cl = 0;
    int uscita = 0;
    int parole = 0;
    char* contents;
    ifstream istr("test.txt");

    if (istr) {
        streambuf * pbuf = istr.rdbuf();
        streamsize size = pbuf->pubseekoff(0, istr.end);
        pbuf->pubseekoff(0, istr.beg);       // rewind
        contents = new char[size];
        pbuf->sgetn(contents, size);
        istr.close();

        ofstream myfile;
        myfile.open("out.txt");

        do {
            string prova("");
            uscita = 0;
            do {
                if (contents[cl] == '\n') {
                    uscita = 1;
                }
                prova += contents[cl];
                cl += 1;
            } while (uscita != 1);
            parole += 1;
            //cout << prova << ":" << md5(prova) << endl;
            myfile << prova << ":" << md5(prova) << endl;
        } while (parole != 9586054);

        myfile.close();
    }
}

int main()
{

    thread t[num_threads];

    //Launch a group of threads
    for (int i = 0; i < num_threads; ++i) {
        t[i] = thread(call_from_thread, i);
    }

    cout << "Launched from the main\n";

    //Join the threads with the main thread
    for (int i = 0; i < num_threads; ++i) {
        t[i].join();
    }

    return 0;
}

Answer 1

您在此处看到的是，所有线程都在读取相同的文件并执行相同的工作。这导致文件必须被读取import { Component, ElementRef, Input, ViewEncapsulation } from '@angular/core'; import { PickList, DomHandler } from 'primeng/primeng'; import { ObjectUtils } from 'primeng/components/utils/objectutils'; @Component({ selector: 'ex-pick-list', templateUrl: 'pick-list.component.html', styleUrls: ['pick-list.component.scss'], encapsulation: ViewEncapsulation.None }) export class PickListComponent extends PickList { constructor(el: ElementRef, domHandler: DomHandler, objectUtils: ObjectUtils) { super(el, domHandler, objectUtils); } } <div class="pick-list-container">  <div class="custom-buttons"> <button pButton type="button" (click)="moveRight()" class="ui-[label]="''"></button> </div> </div> </div>次，可能导致约num_threads的速度减慢（因为文件I / O可能在关键路径上）或者甚至更多因为更多的缓存未命中

您可以尝试将整个文件读入内存，在线程之间拆分，然后让每个线程处理该文件内容的子集。

多线程MD5哈希

1 个答案: