std::shared_future
From cppreference.com
Defined in header
<future>
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template< class T > class shared_future;
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(1) | (since C++11) |
template< class T > class shared_future<T&>;
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(2) | (since C++11) |
template<> class shared_future<void>;
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(3) | (since C++11) |
This section is incomplete |
Contents |
[edit] Member functions
constructs the future object (public member function) |
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destructs the future object (public member function) |
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assigns the contents (public member function) |
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Getting the result |
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returns the result (public member function) |
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State |
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checks if the future has a shared state (public member function) |
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waits for the result to become available (public member function) |
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waits for the result, returns if it is not available for the specified timeout duration (public member function) |
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waits for the result, returns if it is not available until specified time point has been reached (public member function) |
[edit] Example
A shared_future
may be used to signal multiple threads simultaneously, similar to std::condition_variable::notify_all()
Run this code
#include <iostream> #include <future> #include <chrono> int main() { std::promise<void> ready_promise, t1_ready_promise, t2_ready_promise; std::shared_future<void> ready_future(ready_promise.get_future()); std::chrono::time_point<std::chrono::high_resolution_clock> start; auto fun1 = [&]() -> std::chrono::duration<double, std::milli> { t1_ready_promise.set_value(); ready_future.wait(); // waits for the signal from main() return std::chrono::high_resolution_clock::now() - start; }; auto fun2 = [&]() -> std::chrono::duration<double, std::milli> { t2_ready_promise.set_value(); ready_future.wait(); // waits for the signal from main() return std::chrono::high_resolution_clock::now() - start; }; auto result1 = std::async(std::launch::async, fun1); auto result2 = std::async(std::launch::async, fun2); // wait for the threads to become ready t1_ready_promise.get_future().wait(); t2_ready_promise.get_future().wait(); // the threads are ready, start the clock start = std::chrono::high_resolution_clock::now(); // signal the threads to go ready_promise.set_value(); std::cout << "Thread 1 received the signal " << result1.get().count() << " ms after start\n" << "Thread 2 received the signal " << result2.get().count() << " ms after start\n"; }
Possible output:
Thread 1 received the signal 0.072 ms after start Thread 2 received the signal 0.041 ms after start