实际上，C++11中对异步的支持不比Python和JavaScript弱，就是有点长。

#include <iostream>

#include <vector>

#include <algorithm>

#include <future>

#include <numeric> 

template <typename RAIter>

int parallel_sum(RAIter front, RAIter beg, RAIter end)

{

  auto len = end - beg;

  if (len < 1000)

    {

      char out[50];

      sprintf(out, "Calculate from %d to %d\n", beg - front, end - front);

      std::cout << out;

      return std::accumulate(beg, end, 0);

    }

  RAIter mid = beg + len / 2;

  auto handle_right = std::async(std::launch::async, parallel_sum<RAIter>, front, mid, end);

  auto handle_left = std::async(std::launch::async,parallel_sum<RAIter>, front, beg, mid);

  return handle_left.get() + handle_right.get();

}

int main()

{

  std::vector<int> v(20000, 1);

  std::cout << "The sum is " << parallel_sum(v.begin(), v.begin(), v.end()) << '\n';

}

一个小插曲，这里编译的时候用g++直接-o，结果疯狂出错。最后发现要加上-pthread参数才能正常使用，看来gcc操作也要多学习

结果1

Calculate from 9375 to 10000

Calculate from 6875 to 7500

Calculate from 6250 to 6875

Calculate from 14375 to 15000

Calculate from 5625 to 6250

Calculate from 16875 to 17500

Calculate from 8750 to 9375

Calculate from 8125 to 8750

Calculate from 5000 to 5625

Calculate from 19375 to 20000

Calculate from 11875 to 12500

Calculate from 13125 to 13750

Calculate from 16250 to 16875

Calculate from 7500 to 8125

Calculate from 13750 to 14375

Calculate from 11250 to 11875

Calculate from 1250 to 1875

Calculate from 1875 to 2500

Calculate from 10625 to 11250

Calculate from 4375 to 5000

Calculate from 10000 to 10625

Calculate from 18125 to 18750

Calculate from 17500 to 18125

Calculate from 3750 to 4375

Calculate from 18750 to 19375

Calculate from 15625 to 16250

Calculate from 15000 to 15625

Calculate from 12500 to 13125

Calculate from 625 to 1250

Calculate from 2500 to 3125

Calculate from 3125 to 3750

Calculate from 0 to 625

The sum is 20000

结果2：

Calculate from 18125 to 18750

Calculate from 9375 to 10000

Calculate from 4375 to 5000

Calculate from 18750 to 19375

Calculate from 13750 to 14375

Calculate from 6875 to 7500

Calculate from 15625 to 16250

Calculate from 11875 to 12500

Calculate from 3750 to 4375

Calculate from 1875 to 2500

Calculate from 6250 to 6875

Calculate from 16250 to 16875

Calculate from 11250 to 11875

Calculate from 10625 to 11250

Calculate from 13125 to 13750

Calculate from 19375 to 20000

Calculate from 14375 to 15000

Calculate from 12500 to 13125

Calculate from 8750 to 9375

Calculate from 8125 to 8750

Calculate from 17500 to 18125

Calculate from 16875 to 17500

Calculate from 5625 to 6250

Calculate from 10000 to 10625

Calculate from 15000 to 15625

Calculate from 1250 to 1875

Calculate from 7500 to 8125

Calculate from 625 to 1250

Calculate from 0 to 625

Calculate from 2500 to 3125

Calculate from 3125 to 3750

Calculate from 5000 to 5625

The sum is 20000

如果在输出中间信息的时候不先在字符串里输出会很乱，因为同一行cout输出不同项的操作不是原子的，中间可能会转到其他线程去。还是要看编译器在汇编时如何工作比较好。