Question

I am reading C++ concurrency in action by Anthony Williams.
I was trying to run a sample program implementing std::promise but its giving an error. Please let me know if anyone can help. Thanks.

Code :-

    #include <iostream>
    #include <future>
    #include <thread>

    using namespace std;

    int myValue(int i,promise<int> intPromise)
    {
        cout<<"In myValue()"<<endl;
        intPromise.set_value(i);
    }

    int main()
    {
        cout<<"In main()"<<endl;
        promise<int> myPromise;
        future<int> result=myPromise.get_future();
        thread myThread(myValue,10,move(myPromise));
        cout<<"Value : "<<result.get()<<endl;
    }

I am not getting any error during compilation but while running this program i get following error.

terminate called without an active exception
Aborted (core dumped)

Though i am getting the output but i am also getting this error with it.
I am using g++ 4.7.0 on Fedora 17. Please help.

Answer 1

Looks like the main thread has finished before myThread. In order to block main thread you should use std::thread::join().

Like this:

#include <iostream>
#include <future>
#include <thread>

using namespace std;

void myValue(int i, promise<int> intPromise)
{
        cout << "In myValue()" << endl;
        intPromise.set_value(i);
}

int main()
{
        promise<int> myPromise;
        future<int> result = myPromise.get_future();

        thread myThread(myValue, 10, move(myPromise));
        myThread.join();

        cout << "Value : " << result.get() << endl;
}