gistfile1.cpp

#include <iostream>
#include <vector>

#define BOOST_THREAD_PROVIDES_FUTURE
#define BOOST_THREAD_PROVIDES_FUTURE_CONTINUATION
#define BOOST_THREAD_PROVIDES_FUTURE_WHEN_ALL_WHEN_ANY
#include <boost/thread/future.hpp>

using namespace boost;

#if 1

int main() {
   future<int> f1 = async([]() { return 1; });
   future<int> f2 = async([]() { return 2; });
   future<int> f3 = async([]() { return 3; });

   f1.then([](decltype(f1) res) {
      std::cout << "f1 done" << std::endl;

   });

   f2.then([](decltype(f2) res) {
      std::cout << "f2 done" << std::endl;
   });

   f3.then([](decltype(f3) res) {
      std::cout << "f3 done" << std::endl;
   });

   auto f12 = when_all(std::move(f1), std::move(f2));

   auto f12d = f12.then([](decltype(f12)) {
      std::cout << "f12 done" << std::endl;
   });

   auto f23 = when_all(std::move(f2), std::move(f3));

   auto f23d = f23.then([](decltype(f23)) {
      std::cout << "f23 done" << std::endl;
   });

   auto f123 = when_all(std::move(f12d), std::move(f23d));

   auto fall = f123.then([](decltype(f123)) {
      std::cout << "all done" << std::endl;
   });

   fall.get();
}

#else

int main() {
   std::vector<future<int>> futures = {
      async([]() { return 1; }),
      async([]() { return 2; })
   };

   future<std::vector<future<int>>> f3 = when_all(std::begin(futures), std::end(futures));

   auto f4 = f3.then([](decltype(f3)) {
      std::cout << "done" << std::endl;
   });

   f4.get();
}

#endif