THUAI6/CAPI/cpp/grpc/include/absl/cleanup/internal/cleanup.h

// Copyright 2021 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// 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.

#ifndef ABSL_CLEANUP_INTERNAL_CLEANUP_H_
#define ABSL_CLEANUP_INTERNAL_CLEANUP_H_

#include <new>
#include <type_traits>
#include <utility>

#include "absl/base/internal/invoke.h"
#include "absl/base/macros.h"
#include "absl/base/thread_annotations.h"
#include "absl/utility/utility.h"

namespace absl
{
    ABSL_NAMESPACE_BEGIN

    namespace cleanup_internal
    {

        struct Tag
        {
        };

        template<typename Arg, typename... Args>
        constexpr bool WasDeduced()
        {
            return (std::is_same<cleanup_internal::Tag, Arg>::value) &&
                   (sizeof...(Args) == 0);
        }

        template<typename Callback>
        constexpr bool ReturnsVoid()
        {
            return (std::is_same<base_internal::invoke_result_t<Callback>, void>::value);
        }

        template<typename Callback>
        class Storage
        {
        public:
            Storage() = delete;

            explicit Storage(Callback callback)
            {
                // Placement-new into a character buffer is used for eager destruction when
                // the cleanup is invoked or cancelled. To ensure this optimizes well, the
                // behavior is implemented locally instead of using an absl::optional.
                ::new (GetCallbackBuffer()) Callback(std::move(callback));
                is_callback_engaged_ = true;
            }

            Storage(Storage&& other)
            {
                ABSL_HARDENING_ASSERT(other.IsCallbackEngaged());

                ::new (GetCallbackBuffer()) Callback(std::move(other.GetCallback()));
                is_callback_engaged_ = true;

                other.DestroyCallback();
            }

            Storage(const Storage& other) = delete;

            Storage& operator=(Storage&& other) = delete;

            Storage& operator=(const Storage& other) = delete;

            void* GetCallbackBuffer()
            {
                return static_cast<void*>(+callback_buffer_);
            }

            Callback& GetCallback()
            {
                return *reinterpret_cast<Callback*>(GetCallbackBuffer());
            }

            bool IsCallbackEngaged() const
            {
                return is_callback_engaged_;
            }

            void DestroyCallback()
            {
                is_callback_engaged_ = false;
                GetCallback().~Callback();
            }

            void InvokeCallback() ABSL_NO_THREAD_SAFETY_ANALYSIS
            {
                std::move(GetCallback())();
            }

        private:
            bool is_callback_engaged_;
            alignas(Callback) char callback_buffer_[sizeof(Callback)];
        };

    }  // namespace cleanup_internal

    ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_CLEANUP_INTERNAL_CLEANUP_H_