Shows results of `wait_for` on a deferred function.

deferred_function.cc

#include <chrono>
#include <future>
#include <iostream>
#include <string>
#include <thread>
 
void DoStuff() {
  std::cout << "Starting task.\n";
  std::this_thread::sleep_for(std::chrono::seconds(2));
}
 
std::string WaitFor(std::future<void>& future) {
  const std::chrono::seconds timeout(1);
  auto start(std::chrono::steady_clock::now());
  auto result(future.wait_for(timeout));
  std::string status(result == std::future_status::ready ? "ready" :
                     result == std::future_status::timeout ? "timeout" : "deferred");
  std::string blocked(std::chrono::steady_clock::now() - start >= timeout ?
                      "blocked" : "not blocked");
  return std::string("status: ") + status + '\t' + blocked + '\n';
}
 
int main() {
  auto deferred_future(std::async(std::launch::deferred, DoStuff));
  std::string result("deferred_future -  " + WaitFor(deferred_future));
  std::cout << result;
 
  auto async_future(std::async(std::launch::async, DoStuff));
  result = "async_future -     " + WaitFor(async_future);
  std::cout << result;
 
  std::promise<void> promise;
  auto promise_future(promise.get_future());
  result = "promise_future -   " + WaitFor(promise_future);
  std::cout << result;
 
  return 0;
}