std::shared_future<T>:: wait

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

May throw implementation-defined exceptions.

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 <chrono>
#include <future>
#include <iostream>
#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(40); });
    std::shared_future<int> f2 = std::async(std::launch::async, []() { return fib(43); });
 
    std::cout << "waiting... " << std::flush;
    const auto start = std::chrono::system_clock::now();
 
    f1.wait();
    f2.wait();
 
    const auto diff = std::chrono::system_clock::now() - start;
    std::cout << std::chrono::duration<double>(diff).count() << " seconds\n";
 
    std::cout << "f1: " << f1.get() << '\n';
    std::cout << "f2: " << f2.get() << '\n';
}

waiting... 1.61803 seconds
f1: 102334155
f2: 433494437

See also