std::shared_future<T>::wait
From cppreference.com
< cpp | thread | shared future
| 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 <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'; }
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 timeout duration (public member function) | |
| waits for the result, returns if it is not available until specified time point has been reached (public member function) |