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.

[edit] Parameters

(none)

[edit] Return value

(none)

[edit] Exceptions

May throw implementation-defined exceptions.

[edit] 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.

[edit] 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

[edit] See also

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