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NaiveFuture
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| #include <variant> | |
| #include <functional> | |
| #include <memory> | |
| #include <iostream> | |
| #include <thread> | |
| #include <chrono> | |
| #include <stdexcept> | |
| #include <Windows.h> | |
| using Win32Handle = std::unique_ptr<void, void (*)(void *) noexcept>; | |
| Win32Handle MakeWin32Handle(void *handle) | |
| { | |
| return Win32Handle{handle, +[](void *h) noexcept {::CloseHandle(h);}}; | |
| } | |
| struct Done {}; | |
| template <typename T> | |
| struct Payload | |
| { | |
| Win32Handle Event; | |
| std::function<T()> Func; | |
| std::variant<std::monostate, std::exception_ptr, T, Done> Data; | |
| template <typename F> | |
| Payload(F f) | |
| : Func{std::move(f)}, | |
| Event{MakeWin32Handle(::CreateEventW({}, FALSE, FALSE, {}))} | |
| { | |
| assert(Event); | |
| } | |
| }; | |
| template <typename T> | |
| class Future | |
| { | |
| public: | |
| T get() | |
| { | |
| const auto waitResult = WaitForSingleObject(payload_->Event.get(), INFINITE); | |
| if (waitResult == WAIT_OBJECT_0) | |
| { | |
| switch (payload_->Data.index()) | |
| { | |
| case 1: | |
| done(); | |
| std::rethrow_exception(std::get<1>(payload_->Data)); | |
| case 2: | |
| { | |
| const auto result = std::get<2>(std::move(payload_->Data)); | |
| done(); | |
| return result; | |
| } | |
| default: | |
| std::terminate(); | |
| } | |
| } | |
| else | |
| { | |
| throw std::system_error{static_cast<int>(::GetLastError()), std::system_category()}; | |
| } | |
| } | |
| ~Future() | |
| { | |
| if (payload_->Data.index() != 3) { | |
| WaitForSingleObject(payload_->Event.get(), INFINITE); | |
| done(); | |
| } | |
| } | |
| Future(std::unique_ptr<Payload<T>> payload) | |
| : payload_{std::move(payload)} | |
| { | |
| } | |
| private: | |
| void done() | |
| { | |
| payload_->Data = Done{}; | |
| } | |
| template <typename F> | |
| friend Future<T> Async(F f); | |
| std::unique_ptr<Payload<T>> payload_; | |
| }; | |
| template <typename F> | |
| Future<std::invoke_result_t<F>> Async(F f) | |
| { | |
| using Result = std::invoke_result_t<F>; | |
| auto payload = std::make_unique<Payload<Result>>(std::move(f)); | |
| ::QueueUserWorkItem(+[](void *param) -> DWORD { | |
| const auto p = static_cast<Payload<Result> *>(param); | |
| { | |
| try | |
| { | |
| p->Data = std::invoke(p->Func); | |
| } | |
| catch (...) | |
| { | |
| p->Data = std::current_exception(); | |
| } | |
| } | |
| SetEvent(p->Event.get()); | |
| return 0; | |
| }, payload.get(), WT_EXECUTEDEFAULT); | |
| return Future{std::move(payload)}; | |
| } | |
| int main() | |
| { | |
| using namespace std::literals; | |
| auto f = Async([]() { | |
| std::cout << "Hello, world!"; | |
| std::this_thread::sleep_for(3s); | |
| return 2; | |
| }); | |
| //std::this_thread::sleep_for(3s); | |
| //std::cout << f.get(); | |
| } |
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