Modern C++ Programming Cookbook

How to do it...

To communicate a value from one thread to another through promises and futures, do this:

1. Make a promise available to the thread function through a parameter, for example:

        void produce_value(std::promise<int>& p)        {          // simulate long running operation          {            using namespace std::chrono_literals;            std::this_thread::sleep_for(2s);          }          // continued at 2.        }

2. Call set_value() on the premise to set the result to represent a value or set_exception() to set the result to indicate an exception:

        // continued from 1.        p.set_value(42);

3. Make the future associated with the premise available to the other thread function through a parameter, for example:

        void consume_value(std::future<int>& f)        {          // continued at 4.        }

4. Call get() on the future ...