std::shared_future<T>::wait

void wait() const;

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

#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';
}

waiting...
f1: 6765
f2: 75025

See also