#include <vector>
#include <iostream>
#include <thread>
#include <future>
#include <cmath>

using namespace std;
#define iterationNumber 1000000

void myFunction(const int index, const int numberInThread, promise<unsigned long>&& p, const vector<int>& numberList) { // const 붙여야 에러 안남 : attempt to use a deleted function
    clock_t begin,end;
int firstIndex = index * numberInThread;
int lastIndex = firstIndex + numberInThread;
vector<int>::const_iterator first = numberList.cbegin() + firstIndex;
vector<int>::const_iterator last = numberList.cbegin() + lastIndex;

vector<int> numbers(first,last);

unsigned long result = 0;

    begin = clock();
for(int i = 0 ; i < numbers.size(); i++) {
        result += numbers.at(i);
    }
    end = clock();
    cout << "thread" << index << " took " << ((float)(end-begin))/CLOCKS_PER_SEC << endl;

    p.set_value(result);

}


int main(void)
{
vector<int> numberList;
vector<thread> t;
vector<future<unsigned long>> futures;
vector<unsigned long> result;
const int NumberOfThreads = thread::hardware_concurrency() ?: 2;
int numberInThread = iterationNumber / NumberOfThreads;

clock_t begin,end;


for(int i = 0 ; i < iterationNumber ; i++) {
int randomN =  rand() % 10000 + 1;
        numberList.push_back(randomN);
    }

for(int j = 0 ; j < NumberOfThreads; j++){
promise<unsigned long> promises;
        futures.push_back(promises.get_future());
        t.push_back(thread(myFunction, j, numberInThread, std::move(promises), numberList));
    }

    for_each(t.begin(), t.end(), std::mem_fn(&std::thread::join));

for (int i = 0; i < futures.size(); i++) {
        result.push_back(futures.at(i).get());
    }

unsigned long RRR = 0;

    begin = clock();
for(int i = 0 ; i < numberList.size(); i++) {
        RRR += numberList.at(i);
    }
    end = clock();
    cout << "not by thread took " << ((float)(end-begin))/CLOCKS_PER_SEC << endl;

}