future/example5.cpp

#include <thread>
#include <future>
#include <cctype>
#include <vector>
#include <algorithm>
#include <iterator>
#include <iostream>
#include <sstream>
int main()
{
 std::istringstream iss_numbers{"3 4 1 42 23 -23 93 2 -289 93"};
 std::istringstream iss_letters{" a 23 b,e a2 k k?a;si,ksa c"};

 std::vector<int> numbers;
 std::vector<char> letters;
 std::promise<void> numbers_promise, letters_promise;

 auto numbers_ready = numbers_promise.get_future();
 auto letter_ready = letters_promise.get_future();

 std::thread value_reader([&]
 {
     // I/O operations.
     std::copy(std::istream_iterator<int>{iss_numbers},
               std::istream_iterator<int>{},
               std::back_inserter(numbers));

     //Notify for numbers.
     numbers_promise.set_value();

     std::copy_if(std::istreambuf_iterator<char>{iss_letters},
                  std::istreambuf_iterator<char>{},
                  std::back_inserter(letters),
                  ::isalpha);

     //Notify for letters.
     letters_promise.set_value();
 });

 numbers_ready.wait();

 std::sort(numbers.begin(), numbers.end());
 if (letter_ready.wait_for(std::chrono::seconds(1)) ==
         std::future_status::timeout)
 {
     //output the numbers while letters are being obtained.
     for (int num : numbers) std::cout << num << ' ';
     numbers.clear(); //Numbers were already printed.
 }

 letter_ready.wait();
 std::sort(letters.begin(), letters.end());

 //If numbers were already printed, it does nothing.
 for (int num : numbers) std::cout << num << ' ';
 std::cout << '\n';

 for (char let : letters) std::cout << let << ' ';
 std::cout << '\n';

 value_reader.join();
 return 0;
}