std::shared_future<T>::wait (3) - Linux Manuals

std::shared_future<T>::wait: std::shared_future<T>::wait

NAME

std::shared_future<T>::wait - std::shared_future<T>::wait

Synopsis

void wait() const; (since C++11)

Blocks until the result becomes available. valid() == true after the call.
The behavior is undefined if valid()== false before the call to this function.

Parameters

(none)

Return value

(none)

Exceptions

(none)

Notes

The implementations are encouraged to detect the case when valid == false before the call and throw a std::future_error with an error condition of std::future_errc::no_state.
Calling wait on the same std::shared_future from multiple threads is not safe; the intended use is for each thread that waits on the same shared state to have a copy of a std::shared_future.

Example

// Run this code

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

  int fib(int n)
  {
    if (n < 3) return 1;
    else return fib(n-1) + fib(n-2);
  }

  int main()
  {
      std::shared_future<int> f1 = std::async(std::launch::async, [](){
          return fib(20);
      });
      std::shared_future<int> f2 = std::async(std::launch::async, [](){
          return fib(25);
      });

      std::cout << "waiting...\n";
      f1.wait();
      f2.wait();

      std::cout << "f1: " << f1.get() << '\n';
      std::cout << "f2: " << f2.get() << '\n';
  }

Output:

  waiting...
  f1: 6765
  f2: 75025