simple nonblocking read from std::cin

nonblocking.cpp

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

std::string GetLineFromCin() {
    std::string line;
    std::getline(std::cin, line);
    return line;
}

int main() {

    auto future = std::async(std::launch::async, GetLineFromCin);

    while (true) {
        if (future.wait_for(std::chrono::seconds(0)) == std::future_status::ready) {
            auto line = future.get();

            // Set a new line. Subtle race condition between the previous line
            // and this. Some lines could be missed. To aleviate, you need an
            // io-only thread. I'll give an example of that as well.
            future = std::async(std::launch::async, GetLineFromCin);

            std::cout << "you wrote " << line << std::endl;
        }

        std::cout << "waiting..." << std::endl;
        std::this_thread::sleep_for(std::chrono::seconds(1));
    }
}

@vmrob I like this approach. A small notice only: instead of calling sleep at the end of the while loop, why don't you put std::chrono::seconds(1) in the wait_for instead?

i think he wants mutex (critical condition) to be over as fast as possible, so he doesn't block the io thread