蓝桥ROS机器人之现代C++学习笔记7.3 期物

// future example
#include <iostream>       // std::cout
#include <future>         // std::async, std::future
#include <chrono>         // std::chrono::milliseconds

// a non-optimized way of checking for prime numbers:
bool is_prime (int x) {
  for (int i=2; i<x; ++i) if (x%i==0) return false;
  return true;
}

int main ()
{
  // call function asynchronously:
  std::future<bool> fut = std::async (is_prime,444444443); 

  // do something while waiting for function to set future:
  std::cout << "checking, please wait";
  std::chrono::milliseconds span (100);
  while (fut.wait_for(span)==std::future_status::timeout)
    std::cout << '.' << std::flush;

  bool x = fut.get();     // retrieve return value

  std::cout << "\n444444443 " << (x?"is":"is not") << " prime.\n";

  return 0;
}

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

int main() {
    // pack a lambda expression that returns 7 into a std::packaged_task
    std::packaged_task<int()> task([](){return 7;});
    // get the future of task
    std::future<int> result = task.get_future();    // run task in a thread
    std::thread(std::move(task)).detach();
    std::cout << "waiting...";
    result.wait(); // block until future has arrived
    // output result
    std::cout << "done!" << std:: endl << "future result is " << result.get() << std::endl;
    return 0;
}