std::future::wait (3) Linux Manual Page

std::future<T>::wait – std::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.

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

See also

           waits for the result, returns if it is not available for the specified timeout duration
wait_for (public member function)
           waits for the result, returns if it is not available until specified time point has been reached
wait_until (public member function)