NAME¶

std::shared_future::wait - std::shared_future::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¶

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¶

// Run this code

#include <chrono>
#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(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';
}

Possible output:¶

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

See also¶

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