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Diffstat (limited to 'src/msg/async/dpdk/shared_ptr.h')
| -rw-r--r-- | src/msg/async/dpdk/shared_ptr.h | 391 |
1 files changed, 391 insertions, 0 deletions
diff --git a/src/msg/async/dpdk/shared_ptr.h b/src/msg/async/dpdk/shared_ptr.h new file mode 100644 index 00000000..d078063b --- /dev/null +++ b/src/msg/async/dpdk/shared_ptr.h @@ -0,0 +1,391 @@ +// -*- mode:C++; tab-width:8; c-basic-offset:4; indent-tabs-mode:nil -*- +/* + * This file is open source software, licensed to you under the terms + * of the Apache License, Version 2.0 (the "License"). See the NOTICE file + * distributed with this work for additional information regarding copyright + * ownership. 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. + */ +/* + * Copyright (C) 2014 Cloudius Systems, Ltd. + */ + +#ifndef CEPH_LW_SHARED_PTR_H_ +#define CEPH_LW_SHARED_PTR_H_ + +#include <utility> +#include <type_traits> +#include <functional> +#include <iostream> + +// This header defines a shared pointer facility, lw_shared_ptr<>, +// modeled after std::shared_ptr<>. +// +// Unlike std::shared_ptr<>, this implementation is thread +// safe, and two pointers sharing the same object must not be used in +// different threads. +// +// lw_shared_ptr<> is the more lightweight variant, with a lw_shared_ptr<> +// occupying just one machine word, and adding just one word to the shared +// object. However, it does not support polymorphism. +// +// It supports shared_from_this() via enable_shared_from_this<> +// and lw_enable_shared_from_this<>(). +// + +template <typename T> +class lw_shared_ptr; + +template <typename T> +class enable_lw_shared_from_this; + +template <typename T> +class enable_shared_from_this; + +template <typename T, typename... A> +lw_shared_ptr<T> make_lw_shared(A&&... a); + +template <typename T> +lw_shared_ptr<T> make_lw_shared(T&& a); + +template <typename T> +lw_shared_ptr<T> make_lw_shared(T& a); + +struct lw_shared_ptr_counter_base { + long _count = 0; +}; + + +namespace internal { + +template <class T, class U> +struct lw_shared_ptr_accessors; + +template <class T> +struct lw_shared_ptr_accessors_esft; + +template <class T> +struct lw_shared_ptr_accessors_no_esft; + +} + + +// We want to support two use cases for shared_ptr<T>: +// +// 1. T is any type (primitive or class type) +// +// 2. T is a class type that inherits from enable_shared_from_this<T>. +// +// In the first case, we must wrap T in an object containing the counter, +// since T may be a primitive type and cannot be a base class. +// +// In the second case, we want T to reach the counter through its +// enable_shared_from_this<> base class, so that we can implement +// shared_from_this(). +// +// To implement those two conflicting requirements (T alongside its counter; +// T inherits from an object containing the counter) we use std::conditional<> +// and some accessor functions to select between two implementations. + + +// CRTP from this to enable shared_from_this: +template <typename T> +class enable_lw_shared_from_this : private lw_shared_ptr_counter_base { + using ctor = T; +protected: + enable_lw_shared_from_this() noexcept {} + enable_lw_shared_from_this(enable_lw_shared_from_this&&) noexcept {} + enable_lw_shared_from_this(const enable_lw_shared_from_this&) noexcept {} + enable_lw_shared_from_this& operator=(const enable_lw_shared_from_this&) noexcept { return *this; } + enable_lw_shared_from_this& operator=(enable_lw_shared_from_this&&) noexcept { return *this; } +public: + lw_shared_ptr<T> shared_from_this(); + lw_shared_ptr<const T> shared_from_this() const; + + template <typename X> + friend class lw_shared_ptr; + template <typename X> + friend class ::internal::lw_shared_ptr_accessors_esft; + template <typename X, class Y> + friend class ::internal::lw_shared_ptr_accessors; +}; + +template <typename T> +struct shared_ptr_no_esft : private lw_shared_ptr_counter_base { + T _value; + + shared_ptr_no_esft() = default; + shared_ptr_no_esft(const T& x) : _value(x) {} + shared_ptr_no_esft(T&& x) : _value(std::move(x)) {} + template <typename... A> + shared_ptr_no_esft(A&&... a) : _value(std::forward<A>(a)...) {} + + template <typename X> + friend class lw_shared_ptr; + template <typename X> + friend class ::internal::lw_shared_ptr_accessors_no_esft; + template <typename X, class Y> + friend class ::internal::lw_shared_ptr_accessors; +}; + + +/// Extension point: the user may override this to change how \ref lw_shared_ptr objects are destroyed, +/// primarily so that incomplete classes can be used. +/// +/// Customizing the deleter requires that \c T be derived from \c enable_lw_shared_from_this<T>. +/// The specialization must be visible for all uses of \c lw_shared_ptr<T>. +/// +/// To customize, the template must have a `static void dispose(T*)` operator that disposes of +/// the object. +template <typename T> +struct lw_shared_ptr_deleter; // No generic implementation + +namespace internal { + +template <typename T> +struct lw_shared_ptr_accessors_esft { + using concrete_type = std::remove_const_t<T>; + static T* to_value(lw_shared_ptr_counter_base* counter) { + return static_cast<T*>(counter); + } + static void dispose(lw_shared_ptr_counter_base* counter) { + delete static_cast<T*>(counter); + } + static void instantiate_to_value(lw_shared_ptr_counter_base* p) { + // since to_value() is defined above, we don't need to do anything special + // to force-instantiate it + } +}; + +template <typename T> +struct lw_shared_ptr_accessors_no_esft { + using concrete_type = shared_ptr_no_esft<T>; + static T* to_value(lw_shared_ptr_counter_base* counter) { + return &static_cast<concrete_type*>(counter)->_value; + } + static void dispose(lw_shared_ptr_counter_base* counter) { + delete static_cast<concrete_type*>(counter); + } + static void instantiate_to_value(lw_shared_ptr_counter_base* p) { + // since to_value() is defined above, we don't need to do anything special + // to force-instantiate it + } +}; + +// Generic case: lw_shared_ptr_deleter<T> is not specialized, select +// implementation based on whether T inherits from enable_lw_shared_from_this<T>. +template <typename T, typename U = void> +struct lw_shared_ptr_accessors : std::conditional_t< + std::is_base_of<enable_lw_shared_from_this<T>, T>::value, + lw_shared_ptr_accessors_esft<T>, + lw_shared_ptr_accessors_no_esft<T>> { +}; + +// Overload when lw_shared_ptr_deleter<T> specialized +template <typename T> +struct lw_shared_ptr_accessors<T, std::void_t<decltype(lw_shared_ptr_deleter<T>{})>> { + using concrete_type = T; + static T* to_value(lw_shared_ptr_counter_base* counter); + static void dispose(lw_shared_ptr_counter_base* counter) { + lw_shared_ptr_deleter<T>::dispose(to_value(counter)); + } + static void instantiate_to_value(lw_shared_ptr_counter_base* p) { + // instantiate to_value(); must be defined by shared_ptr_incomplete.hh + to_value(p); + } +}; + +} + +template <typename T> +class lw_shared_ptr { + using accessors = ::internal::lw_shared_ptr_accessors<std::remove_const_t<T>>; + using concrete_type = typename accessors::concrete_type; + mutable lw_shared_ptr_counter_base* _p = nullptr; +private: + lw_shared_ptr(lw_shared_ptr_counter_base* p) noexcept : _p(p) { + if (_p) { + ++_p->_count; + } + } + template <typename... A> + static lw_shared_ptr make(A&&... a) { + auto p = new concrete_type(std::forward<A>(a)...); + accessors::instantiate_to_value(p); + return lw_shared_ptr(p); + } +public: + using element_type = T; + + lw_shared_ptr() noexcept = default; + lw_shared_ptr(std::nullptr_t) noexcept : lw_shared_ptr() {} + lw_shared_ptr(const lw_shared_ptr& x) noexcept : _p(x._p) { + if (_p) { + ++_p->_count; + } + } + lw_shared_ptr(lw_shared_ptr&& x) noexcept : _p(x._p) { + x._p = nullptr; + } + [[gnu::always_inline]] + ~lw_shared_ptr() { + if (_p && !--_p->_count) { + accessors::dispose(_p); + } + } + lw_shared_ptr& operator=(const lw_shared_ptr& x) noexcept { + if (_p != x._p) { + this->~lw_shared_ptr(); + new (this) lw_shared_ptr(x); + } + return *this; + } + lw_shared_ptr& operator=(lw_shared_ptr&& x) noexcept { + if (_p != x._p) { + this->~lw_shared_ptr(); + new (this) lw_shared_ptr(std::move(x)); + } + return *this; + } + lw_shared_ptr& operator=(std::nullptr_t) noexcept { + return *this = lw_shared_ptr(); + } + lw_shared_ptr& operator=(T&& x) noexcept { + this->~lw_shared_ptr(); + new (this) lw_shared_ptr(make_lw_shared<T>(std::move(x))); + return *this; + } + + T& operator*() const noexcept { return *accessors::to_value(_p); } + T* operator->() const noexcept { return accessors::to_value(_p); } + T* get() const noexcept { + if (_p) { + return accessors::to_value(_p); + } else { + return nullptr; + } + } + + long int use_count() const noexcept { + if (_p) { + return _p->_count; + } else { + return 0; + } + } + + operator lw_shared_ptr<const T>() const noexcept { + return lw_shared_ptr<const T>(_p); + } + + explicit operator bool() const noexcept { + return _p; + } + + bool owned() const noexcept { + return _p->_count == 1; + } + + bool operator==(const lw_shared_ptr<const T>& x) const { + return _p == x._p; + } + + bool operator!=(const lw_shared_ptr<const T>& x) const { + return !operator==(x); + } + + bool operator==(const lw_shared_ptr<std::remove_const_t<T>>& x) const { + return _p == x._p; + } + + bool operator!=(const lw_shared_ptr<std::remove_const_t<T>>& x) const { + return !operator==(x); + } + + bool operator<(const lw_shared_ptr<const T>& x) const { + return _p < x._p; + } + + bool operator<(const lw_shared_ptr<std::remove_const_t<T>>& x) const { + return _p < x._p; + } + + template <typename U> + friend class lw_shared_ptr; + + template <typename X, typename... A> + friend lw_shared_ptr<X> make_lw_shared(A&&...); + + template <typename U> + friend lw_shared_ptr<U> make_lw_shared(U&&); + + template <typename U> + friend lw_shared_ptr<U> make_lw_shared(U&); + + template <typename U> + friend class enable_lw_shared_from_this; +}; + +template <typename T, typename... A> +inline +lw_shared_ptr<T> make_lw_shared(A&&... a) { + return lw_shared_ptr<T>::make(std::forward<A>(a)...); +} + +template <typename T> +inline +lw_shared_ptr<T> make_lw_shared(T&& a) { + return lw_shared_ptr<T>::make(std::move(a)); +} + +template <typename T> +inline +lw_shared_ptr<T> make_lw_shared(T& a) { + return lw_shared_ptr<T>::make(a); +} + +template <typename T> +inline +lw_shared_ptr<T> +enable_lw_shared_from_this<T>::shared_from_this() { + return lw_shared_ptr<T>(this); +} + +template <typename T> +inline +lw_shared_ptr<const T> +enable_lw_shared_from_this<T>::shared_from_this() const { + return lw_shared_ptr<const T>(const_cast<enable_lw_shared_from_this*>(this)); +} + +template <typename T> +static inline +std::ostream& operator<<(std::ostream& out, const lw_shared_ptr<T>& p) { + if (!p) { + return out << "null"; + } + return out << *p; +} + +namespace std { + + template <typename T> + struct hash<lw_shared_ptr<T>> : private hash<T*> { + size_t operator()(const lw_shared_ptr<T>& p) const { + return hash<T*>::operator()(p.get()); + } + }; + +} + +#endif /* CEPH_LW_SHARED_PTR_H_ */ |