folly/folly/io/async/DelayedDestructionBase.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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
 *
 *     http://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.
 */

#pragma once

#include <assert.h>

#include <cstddef>
#include <cstdint>
#include <functional>
#include <memory>
#include <type_traits>
#include <utility>

#include <folly/Portability.h>

namespace folly {

/**
 * DelayedDestructionBase is a helper class to ensure objects are not deleted
 * while they still have functions executing in a higher stack frame.
 *
 * This is useful for objects that invoke callback functions, to ensure that a
 * callback does not destroy the calling object.
 *
 * Classes needing this functionality should:
 * - derive from DelayedDestructionBase directly
 * - implement onDelayedDestroy which'll be called before the object is
 *   going to be destructed
 * - create a DestructorGuard object on the stack in each public method that
 *   may invoke a callback
 *
 * DelayedDestructionBase does not perform any locking.  It is intended to be
 * used only from a single thread.
 */
class DelayedDestructionBase { … };

inline bool operator==(
    const DelayedDestructionBase::DestructorGuard& left,
    const DelayedDestructionBase::DestructorGuard& right) { … }
inline bool operator!=(
    const DelayedDestructionBase::DestructorGuard& left,
    const DelayedDestructionBase::DestructorGuard& right) { … }
inline bool operator==(
    const DelayedDestructionBase::DestructorGuard& left, std::nullptr_t) { … }
inline bool operator==(
    std::nullptr_t, const DelayedDestructionBase::DestructorGuard& right) { … }
inline bool operator!=(
    const DelayedDestructionBase::DestructorGuard& left, std::nullptr_t) { … }
inline bool operator!=(
    std::nullptr_t, const DelayedDestructionBase::DestructorGuard& right) { … }

template <typename LeftAliasType, typename RightAliasType>
inline bool operator==(
    const DelayedDestructionBase::IntrusivePtr<LeftAliasType>& left,
    const DelayedDestructionBase::IntrusivePtr<RightAliasType>& right) { … }
template <typename LeftAliasType, typename RightAliasType>
inline bool operator!=(
    const DelayedDestructionBase::IntrusivePtr<LeftAliasType>& left,
    const DelayedDestructionBase::IntrusivePtr<RightAliasType>& right) { … }
template <typename LeftAliasType>
inline bool operator==(
    const DelayedDestructionBase::IntrusivePtr<LeftAliasType>& left,
    std::nullptr_t) { … }
template <typename RightAliasType>
inline bool operator==(
    std::nullptr_t,
    const DelayedDestructionBase::IntrusivePtr<RightAliasType>& right) { … }
template <typename LeftAliasType>
inline bool operator!=(
    const DelayedDestructionBase::IntrusivePtr<LeftAliasType>& left,
    std::nullptr_t) { … }
template <typename RightAliasType>
inline bool operator!=(
    std::nullptr_t,
    const DelayedDestructionBase::IntrusivePtr<RightAliasType>& right) { … }
} // namespace folly