37.并行计算汇总

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <thread>
#include <future>
#include <vector>
#include <cstdlib>
#include <mutex>
using namespace std;
#define COUNT 1000000

//创建互斥量
mutex m;

//多线程计算加法
int add(vector<int> *arr,int start,int count)
{
    static mutex m;//只会初始化一次
    int sum(0);//保存结果
    for (int i = 0; i < count; i++)
    {
        sum += (*arr)[start + i];
    }
    {
        //锁定,离开作用区域,自动释放
        lock_guard<mutex> lckg(m);
        cout << "thread=" << this_thread::get_id()
            << ",count=" << count
            << ",sum=" << sum << endl;
    }
    return sum;
}

void main()
{
    vector <int>data(COUNT);//数组,100万个数据
    for (int i = 0; i < COUNT; i++)
    {
        data[i] = (i + 1) % 1000;// 赋值初始化
    }

    vector<future<int>> result;//结果数组,存放结果

    int cpus = thread::hardware_concurrency();//CPU核心的个数

    for (int i = 0; i < cpus * 2; i++)
    {
        int batch_each = COUNT / (cpus * 2);
        //最后一个线程所计算的个数
        if (i == (cpus * 2) - 1)
        {
            batch_each = COUNT - COUNT / (cpus * 2)*i;
        }
        //不断压入结果
        result.push_back(async(add, &data, i*batch_each, batch_each));
        //async直接返回future类型结果
    }

    //汇总
    int lastresult(0);
    for (int i = 0;i<result.size();i++)
    {
        lastresult += result[i].get();//汇总结果
    }
    cout << "结果=" << lastresult << endl;
    
    cin.get();
}