/*std::future is a C++11 class that represents a value or an exception that will be
available in the future. It can be used to retrieve the result of a function
executed in a separate thread of execution.

One way to wait for the result of a std::future is to use the std::future::wait()
member function. wait() blocks the calling thread until the result is available. 
Here is an example of using std::async to launch a function in a separate thread 
and waiting for the result using std::future::wait():*/

#include <iostream>
#include <future>
#include <chrono>

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

int long_running_task() {
    std::cout << "Performing long-running task..." << std::endl;
    std::this_thread::sleep_for(std::chrono::seconds(5));
    std::cout << "Task complete." << std::endl;
    return 42;
}

int main() {
    std::cout << "Starting long-running task..." << std::endl;
    std::future<int> result = std::async(long_running_task);
    std::cout << "Doing other work while the task runs..." << std::endl;
    // ...
    std::cout << "Waiting for result of long-running task..." << std::endl;
    result.wait();
    std::cout << "Retrieving result of long-running task..." << std::endl;
    int task_result = result.get();
    std::cout << "Result of long-running task: " << task_result << std::endl;
    return 0;
}