async.h

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// The MIT License (MIT)
//
// Copyright (c) 2021 Mateusz Pusz
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
 
#pragma once
 
#include <mp-coro/bits/storage.h>
#include <mp-coro/trace.h>
#include <concepts>
#include <coroutine>
#include <thread>
 
namespace mp_coro {
 
template <std::invocable Func>
class async {
  public:
    using return_type = std::invoke_result_t<Func>;
    template <typename F>
    requires std::same_as<std::remove_cvref_t<F>, Func> explicit async(F &&func)
        : func_ {std::forward<F>(func)} {}
 
    decltype(auto)
    operator co_await() & = delete; // async should be co_awaited only once (on rvalue)
    decltype(auto) operator co_await() && {
        struct awaiter {
            async &awaitable;
            bool await_ready() const noexcept {
                TRACE_FUNC();
                return false;
            }
            void await_suspend(std::coroutine_handle<> handle) {
                auto work = [&, handle]() {
                    TRACE_FUNC();
                    try {
                        if constexpr (std::is_void_v<return_type>)
                            awaitable.func_();
                        else
                            awaitable.result_.set_value(awaitable.func_());
                    } catch (...) {
                        awaitable.result_.set_exception(std::current_exception());
                    }
                    handle.resume();
                };
 
                TRACE_FUNC();
                std::jthread(work).detach(); // TODO: Fix that (replace with a thread pool)
            }
            decltype(auto) await_resume() {
                TRACE_FUNC();
                return std::move(awaitable.result_).get();
            }
        };
        return awaiter {*this};
    }
 
  private:
    Func func_;
    detail::storage<return_type> result_;
};
 
template <typename F>
async(F) -> async<F>;
 
} // namespace mp_coro