future1.cpp

#include <vector>
#include <numeric>
#include <iostream>
#include <chrono>
#include <thread>
#include <mutex>
#include <condition_variable>

int res = 0;						//保存结果的全局变量
std::mutex mu;						//互斥锁全局变量
std::condition_variable cond;       //全局条件变量
 
void accumulate(std::vector<int>::iterator first,
                std::vector<int>::iterator last)
{
    int sum = std::accumulate(first, last, 0);      //标准库求和函数
    std::unique_lock<std::mutex> locker(mu);
    res = sum;
    locker.unlock();
    cond.notify_one();              // 向一个等待线程发出“条件已满足”的通知
}
 
int main()
{
    std::vector<int> numbers = { 1, 2, 3, 4, 5, 6 };
    std::thread work_thread(accumulate, numbers.begin(), numbers.end());

    std::unique_lock<std::mutex> locker(mu);
    cond.wait(locker, [](){ return res;});   //如果条件变量被唤醒，检查结果是否被改变，为真则直接返回，为假则继续等待
    std::cout << "result=" << res << '\n';
    locker.unlock();
    work_thread.join();         //阻塞等待线程执行完成
 
    getchar();
    return 0;
}