future, packaged_task promise

#include "stdafx.h"
#include <iostream>
#include <vector>
#include <future>		//future 類型
#include <algorithm>
#include <numeric>		//accumulate


template <typename RAIter>
int sum(RAIter beg, RAIter end)
{
	auto len = end - beg;
	if (len < 1000)
		return std::accumulate(beg, end, 0);


	RAIter mid = beg + len / 2;
	auto handle = std::async(std::launch::async, sum<RAIter>, mid, end);	//返回一個future類型對象


	int s = sum(beg, mid);
	return s + handle.get();	//取得future對象的值
}


int _tmain(int argc, _TCHAR* argv[])
{
// 	std::vector<int> v(10000, 2);
// 	std::cout << "the sum is " << sum(v.begin(), v.end()) << "\n";


	std::packaged_task<int()> task([](){return 7; });//包裝函數 
	std::future<int> f1 = task.get_future(); //取得一個future對象
	std::thread(std::move(task)).detach();	//開啓一個線程


	std::future<int> f2 = std::async(std::launch::async, [](){return 8; });	//通過async直接返回future對象


 	std::promise<int> p;
 	std::future<int> f3 = p.get_future(); //將promise和future對象綁定
// 	std::thread([](std::promise<int> p){p.set_value_at_thread_exit(9); }, std::move(p)).detach();


	std::cout << "waiting.." << std::flush;


	f1.wait();
	f2.wait();
//	f3.wait();


	std::cout << "done!"
		<< f1.get() << ' ' << f2.get() << ' ';// << f3.get() << '\n';
    int a;
	
	int b =  std::move(a);		//左值轉換爲右值
	a = 1;
	
	std::cout << "a:" << a << '\n' << "b:" << b << '\n';
}