C++ 异步多线程

用到 C++ future 库，代码如下：

#include <iostream>
#include <future>
#include <unistd.h>
using namespace std;

double f(double a,double b){
    double c = a+b;
    sleep(3);
    return c;
}

int main(){
    double a=1.0,b=2.1;
    future<double> fu = async(f,a,b);
    cout<<"..."<<endl;
    cout<<"result:"<<fu.get()<<endl;
    return 0;
}

编译方式：

g++ -std=c++11 async.cpp -lpthread -o demo

future 无法实现多个线程等待同一个异步线程结果，future 对象调用 get 后会转移控制权，导致只有一个线程可以获取异步线程的返回值，要解决这个问题可以用 shared_future,代码如下：

#include <iostream>
#include <future>
#include <unistd.h>
using namespace std;

double f(double a,double b){
    double c = a+b;
    sleep(3);
    return c;
}

int main(){
    double a=1.0,b=2.1;
    shared_future<double> fu = async(f,a,b);
    shared_future<double> c1 = async(f,a,fu.get());
    shared_future<double> c2 = async(f,a,fu.get());
    cout<<"..."<<endl;
    cout<<"result:"<<c1.get()<<endl;
    cout<<"result:"<<c2.get()<<endl;
    cout<<"result:"<<fu.get()<<endl;
    return 0;
}