xref: /openbmc/sdbusplus/include/sdbusplus/async/stdexec/__detail/__connect_awaitable.hpp (revision 06f265f6)

/*
 * Copyright (c) 2021-2024 NVIDIA Corporation
 *
 * Licensed under the Apache License Version 2.0 with LLVM Exceptions
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *   https://llvm.org/LICENSE.txt
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#pragma once

#include "__awaitable.hpp"
#include "__completion_signatures.hpp"
#include "__concepts.hpp"
#include "__config.hpp"
#include "__execution_fwd.hpp"
#include "__meta.hpp"
#include "__receivers.hpp"
#include "__tag_invoke.hpp"

#include <exception>
#include <utility>

namespace stdexec
{
#if !STDEXEC_STD_NO_COROUTINES()
/////////////////////////////////////////////////////////////////////////////
// __connect_awaitable_
namespace __connect_awaitable_
{
struct __promise_base
{
    auto initial_suspend() noexcept -> __coro::suspend_always
    {
        return {};
    }

    [[noreturn]] auto final_suspend() noexcept -> __coro::suspend_always
    {
        std::terminate();
    }

    [[noreturn]] void unhandled_exception() noexcept
    {
        std::terminate();
    }

    [[noreturn]] void return_void() noexcept
    {
        std::terminate();
    }
};

struct __operation_base
{
    __coro::coroutine_handle<> __coro_;

    explicit __operation_base(__coro::coroutine_handle<> __hcoro) noexcept :
        __coro_(__hcoro)
    {}

    __operation_base(__operation_base&& __other) noexcept :
        __coro_(std::exchange(__other.__coro_, {}))
    {}

    ~__operation_base()
    {
        if (__coro_)
        {
#if STDEXEC_MSVC()
            // MSVCBUG
            // https://developercommunity.visualstudio.com/t/Double-destroy-of-a-local-in-coroutine-d/10456428

            // Reassign __coro_ before calling destroy to make the mutation
            // observable and to hopefully ensure that the compiler does not
            // eliminate it.
            auto __coro = __coro_;
            __coro_ = {};
            __coro.destroy();
#else
            __coro_.destroy();
#endif
        }
    }

    void start() & noexcept
    {
        __coro_.resume();
    }
};

template <class _ReceiverId>
struct __promise;

template <class _ReceiverId>
struct __operation
{
    struct __t : __operation_base
    {
        using promise_type = stdexec::__t<__promise<_ReceiverId>>;
        using __operation_base::__operation_base;
    };
};

template <class _ReceiverId>
struct __promise
{
    using _Receiver = stdexec::__t<_ReceiverId>;

    struct __t : __promise_base
    {
        using __id = __promise;

        explicit __t(auto&, _Receiver& __rcvr) noexcept : __rcvr_(__rcvr) {}

        auto unhandled_stopped() noexcept -> __coro::coroutine_handle<>
        {
            stdexec::set_stopped(static_cast<_Receiver&&>(__rcvr_));
            // Returning noop_coroutine here causes the __connect_awaitable
            // coroutine to never resume past the point where it co_await's
            // the awaitable.
            return __coro::noop_coroutine();
        }

        auto get_return_object() noexcept
            -> stdexec::__t<__operation<_ReceiverId>>
        {
            return stdexec::__t<__operation<_ReceiverId>>{
                __coro::coroutine_handle<__t>::from_promise(*this)};
        }

        template <class _Awaitable>
        auto await_transform(_Awaitable&& __awaitable) noexcept -> _Awaitable&&
        {
            return static_cast<_Awaitable&&>(__awaitable);
        }

        template <class _Awaitable>
            requires tag_invocable<as_awaitable_t, _Awaitable, __t&>
        auto await_transform(_Awaitable&& __awaitable) //
            noexcept(nothrow_tag_invocable<as_awaitable_t, _Awaitable, __t&>)
                -> tag_invoke_result_t<as_awaitable_t, _Awaitable, __t&>
        {
            return tag_invoke(as_awaitable,
                              static_cast<_Awaitable&&>(__awaitable), *this);
        }

        // Pass through the get_env receiver query
        auto get_env() const noexcept -> env_of_t<_Receiver>
        {
            return stdexec::get_env(__rcvr_);
        }

        _Receiver& __rcvr_;
    };
};

template <receiver _Receiver>
using __promise_t = __t<__promise<__id<_Receiver>>>;

template <receiver _Receiver>
using __operation_t = __t<__operation<__id<_Receiver>>>;

struct __connect_awaitable_t
{
  private:
    template <class _Fun, class... _Ts>
    static auto __co_call(_Fun __fun, _Ts&&... __as) noexcept
    {
        auto __fn = [&, __fun]() noexcept {
            __fun(static_cast<_Ts&&>(__as)...);
        };

        struct __awaiter
        {
            decltype(__fn) __fn_;

            static constexpr auto await_ready() noexcept -> bool
            {
                return false;
            }

            void await_suspend(__coro::coroutine_handle<>) noexcept
            {
                __fn_();
            }

            [[noreturn]] void await_resume() noexcept
            {
                std::terminate();
            }
        };

        return __awaiter{__fn};
    }

    template <class _Awaitable, class _Receiver>
#if STDEXEC_GCC() && (__GNUC__ > 11)
    __attribute__((__used__))
#endif
    static auto
        __co_impl(_Awaitable __awaitable,
                  _Receiver __rcvr) -> __operation_t<_Receiver>
    {
        using __result_t = __await_result_t<_Awaitable, __promise_t<_Receiver>>;
        std::exception_ptr __eptr;
        try
        {
            if constexpr (same_as<__result_t, void>)
                co_await (co_await static_cast<_Awaitable&&>(__awaitable),
                          __co_call(set_value,
                                    static_cast<_Receiver&&>(__rcvr)));
            else
                co_await __co_call(
                    set_value, static_cast<_Receiver&&>(__rcvr),
                    co_await static_cast<_Awaitable&&>(__awaitable));
        }
        catch (...)
        {
            __eptr = std::current_exception();
        }
        co_await __co_call(set_error, static_cast<_Receiver&&>(__rcvr),
                           static_cast<std::exception_ptr&&>(__eptr));
    }

    template <receiver _Receiver, class _Awaitable>
    using __completions_t = //
        completion_signatures<
            __minvoke<      // set_value_t() or set_value_t(T)
                __mremove<void, __qf<set_value_t>>,
                __await_result_t<_Awaitable, __promise_t<_Receiver>>>,
            set_error_t(std::exception_ptr), set_stopped_t()>;

  public:
    template <class _Receiver, __awaitable<__promise_t<_Receiver>> _Awaitable>
        requires receiver_of<_Receiver, __completions_t<_Receiver, _Awaitable>>
    auto operator()(_Awaitable&& __awaitable,
                    _Receiver __rcvr) const -> __operation_t<_Receiver>
    {
        return __co_impl(static_cast<_Awaitable&&>(__awaitable),
                         static_cast<_Receiver&&>(__rcvr));
    }
};
} // namespace __connect_awaitable_

using __connect_awaitable_::__connect_awaitable_t;
#else
struct __connect_awaitable_t
{};
#endif
inline constexpr __connect_awaitable_t __connect_awaitable{};
} // namespace stdexec