std::future
cppreference.com
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| <future> .
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template< class T > class future; |
(1) | (since C++11) |
template< class T > class future<T&>; |
(2) | (since C++11) |
template<> class future<void>; |
(3) | (since C++11) |
std::future .:
- (std::async, std::packaged_task, std::promise )
std::future.
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std::future, , . .
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std::future(shared state)-std::promise::set_value- .
std::future (std::shared_future .)
| constructs the future object (public member function) | |
| destructs the future object (public member function) | |
| moves the future object (public member function) | |
transfers the shared state from *this to a shared_future and returns it (public member function) | |
Getting the result | |
| returns the result (public member function) | |
State | |
| checks if the future has a shared state (public member function) | |
| waits for the result to become available (public member function) | |
| 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) | |
#include <iostream>
#include <future>
#include <thread>
int main()
{
// packaged_task future
std::packaged_task<int()> task([](){ return 7; }); //
std::future<int> f1 = task.get_future(); // future
std::thread(std::move(task)).detach(); //
// an async() future
std::future<int> f2 = std::async(std::launch::async, [](){ return 8; });
// promise future
std::promise<int> p;
std::future<int> f3 = p.get_future();
std::thread( [](std::promise<int> p){ p.set_value_at_thread_exit(9); },
std::move(p) ).detach();
std::cout << "Waiting..." << std::flush;
f1.wait();
f2.wait();
f3.wait();
std::cout << "Done!\nResults are: "
<< f1.get() << ' ' << f2.get() << ' ' << f3.get() << '\n';
}
Output:
Waiting...Done!
Results are: 7 8 9
See also
(C++11) |
runs a function asynchronously (potentially in a new thread) and returns a std::future that will hold the result (function template) |
(C++11) |
waits for a value (possibly referenced by other futures) that is set asynchronously (class template) |