C++基礎-並行計算求和(async)

並行計算使用的是async, 通過每一個線程都進行相同的計算，最后在vector<future<int>>result; 將結果進行相加

全部代碼

//
// Created by Administrator on 2021/6/29.
//
#include<iostream>
#include<thread>
#include<future>
#include<vector>
#include<cstdlib>


using namespace std;
#define COUNT 1000000

int add(vector<int>*arr, int start, int count)
{
    static mutex m; //只會初始化一次
    int sum(0); //保存結果的作用
    for(int i = 0; i < count; i++){
        sum += (*arr)[start + i];
    }
    {
        //顯示結果必須, 僅僅計算多余, 加鎖
        lock_guard<mutex> lck(m); //鎖定
        cout << "thread" << this_thread::get_id << ",count" <<
        ",sum=" << sum << endl; //打印結果
    }
    return sum;
}


int main()
{
    vector<int>data(COUNT); //數組, 100萬
    for(int i = 0; i < COUNT; i++)
    {
        data[i] = (i + 1) % 1000; //0-999
    }

    vector<future<int>>result; //結果數組
    int cpus = thread::hardware_concurrency(); //CPU核心的個數
    for(int i = 0; i < cpus * 2; i++)
    {
        int batch_each = COUNT / (cpus * 2); //
        if(i == (cpus * 2) - 1) {
            batch_each = COUNT - COUNT / (cpus * 2) * i; //最后一個承擔更多的計算
        }
        //不斷壓入結果
        result.push_back(async(add, &data, i * batch_each, batch_each)); //返回結果
    }
    int lastresult(0);
    for(int i = 0; i < cpus * 2; i++)
    {
        lastresult += result[i].get();  //匯總結果
    }
    cout << "lastresult=" << lastresult << endl;
    cin.get();
}

//
// Created by Administrator on 2021/6/29.
//
#include<iostream>
#include<thread>
#include<future>
#include<vector>
#include<cstdlib>


using namespace std;
#define COUNT 1000000

int add(vector<int>*arr, int start, int count)
{
    static mutex m; //只會初始化一次
    int sum(0); //保存結果的作用
    for(int i = 0; i < count; i++){
        sum += (*arr)[start + i];
    }
    {
        //顯示結果必須, 僅僅計算多余, 加鎖
        lock_guard<mutex> lck(m); //鎖定
        cout << "thread" << this_thread::get_id << ",count" <<
        ",sum=" << sum << endl; //打印結果
    }
    return sum;
}


int main()
{
    vector<int>data(COUNT); //數組, 100萬
    for(int i = 0; i < COUNT; i++)
    {
        data[i] = (i + 1) % 1000; //0-999
    }

    vector<future<int>>result; //結果數組
    int cpus = thread::hardware_concurrency(); //CPU核心的個數
    for(int i = 0; i < cpus * 2; i++)
    {
        int batch_each = COUNT / (cpus * 2); //
        if(i == (cpus * 2) - 1) {
            batch_each = COUNT - COUNT / (cpus * 2) * i; //最后一個承擔更多的計算
        }
        //不斷壓入結果
        result.push_back(async(add, &data, i * batch_each, batch_each)); //返回結果
    }
    int lastresult(0);
    for(int i = 0; i < cpus * 2; i++)
    {
        lastresult += result[i].get();  //匯總結果
    }
    cout << "lastresult=" << lastresult << endl;
    cin.get();
}