std::future<T>::wait
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std::future
Member functions
Getting the result
State
future::wait
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.
[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 .
[edit] Example
Run this code
#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::future <int> f1 = std::async (std::launch::async, []() { return fib(40); }); std::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
[edit] See also
waits for the result, returns if it is not available for the specified timeout duration
(public member function) [edit]
(public member function) [edit]
waits for the result, returns if it is not available until specified time point has been reached
(public member function) [edit]
(public member function) [edit]