ladybird/AK/IntrusiveList.h
Brian Gianforcaro 8e41d96618 AK: Enable IntrusiveList self reference to be optimized out when empty
If a member is an empty class, the standard normally stats that it needs
to have a size of at least 1 byte in order to guarantee that the
addresses of distinct objects of the same type are always distinct.

However as of c++20, we can use [[no_unique_address]] to instruct the
compiler that if the member has an empty type, it may optimize it to
occupy no space.
2021-08-19 08:07:45 +04:30

456 lines
14 KiB
C++

/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Assertions.h>
#include <AK/BitCast.h>
#include <AK/Forward.h>
#include <AK/Noncopyable.h>
#include <AK/StdLibExtras.h>
namespace AK {
namespace Detail {
template<typename T, typename Container = RawPtr<T>>
class IntrusiveListNode;
template<typename T, typename Container>
struct SubstituteIntrusiveListNodeContainerType {
using Type = Container;
};
template<typename T>
struct SubstituteIntrusiveListNodeContainerType<T, NonnullRefPtr<T>> {
using Type = RefPtr<T>;
};
}
template<typename T, typename Container = RawPtr<T>>
using IntrusiveListNode = Detail::IntrusiveListNode<T, typename Detail::SubstituteIntrusiveListNodeContainerType<T, Container>::Type>;
template<typename T, typename Container>
class IntrusiveListStorage {
private:
friend class Detail::IntrusiveListNode<T, Container>;
template<class T_, typename Container_, IntrusiveListNode<T_, Container_> T_::*member>
friend class IntrusiveList;
IntrusiveListNode<T, Container>* m_first { nullptr };
IntrusiveListNode<T, Container>* m_last { nullptr };
};
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
class IntrusiveList {
AK_MAKE_NONCOPYABLE(IntrusiveList);
AK_MAKE_NONMOVABLE(IntrusiveList);
public:
IntrusiveList() = default;
~IntrusiveList();
void clear();
[[nodiscard]] bool is_empty() const;
[[nodiscard]] size_t size_slow() const;
void append(T& n);
void prepend(T& n);
void insert_before(T&, T&);
void remove(T& n);
[[nodiscard]] bool contains(const T&) const;
[[nodiscard]] Container first() const;
[[nodiscard]] Container last() const;
[[nodiscard]] Container take_first();
[[nodiscard]] Container take_last();
class Iterator {
public:
Iterator() = default;
Iterator(T* value)
: m_value(move(value))
{
}
const T& operator*() const { return *m_value; }
auto operator->() const { return m_value; }
T& operator*() { return *m_value; }
auto operator->() { return m_value; }
bool operator==(const Iterator& other) const { return other.m_value == m_value; }
bool operator!=(const Iterator& other) const { return !(*this == other); }
Iterator& operator++()
{
m_value = IntrusiveList<T, Container, member>::next(m_value);
return *this;
}
Iterator& erase();
private:
T* m_value { nullptr };
};
Iterator begin();
Iterator end() { return Iterator {}; }
class ReverseIterator {
public:
ReverseIterator() = default;
ReverseIterator(T* value)
: m_value(move(value))
{
}
const T& operator*() const { return *m_value; }
auto operator->() const { return m_value; }
T& operator*() { return *m_value; }
auto operator->() { return m_value; }
bool operator==(const ReverseIterator& other) const { return other.m_value == m_value; }
bool operator!=(const ReverseIterator& other) const { return !(*this == other); }
ReverseIterator& operator++()
{
m_value = IntrusiveList<T, Container, member>::prev(m_value);
return *this;
}
ReverseIterator& erase();
private:
T* m_value { nullptr };
};
ReverseIterator rbegin();
ReverseIterator rend() { return ReverseIterator {}; }
class ConstIterator {
public:
ConstIterator() = default;
ConstIterator(const T* value)
: m_value(value)
{
}
const T& operator*() const { return *m_value; }
auto operator->() const { return m_value; }
bool operator==(const ConstIterator& other) const { return other.m_value == m_value; }
bool operator!=(const ConstIterator& other) const { return !(*this == other); }
ConstIterator& operator++()
{
m_value = IntrusiveList<T, Container, member>::next(m_value);
return *this;
}
private:
const T* m_value { nullptr };
};
ConstIterator begin() const;
ConstIterator end() const { return ConstIterator {}; }
private:
static T* next(T* current);
static T* prev(T* current);
static const T* next(const T* current);
static const T* prev(const T* current);
static T* node_to_value(IntrusiveListNode<T, Container>& node);
IntrusiveListStorage<T, Container> m_storage;
};
template<typename Contained, bool _IsRaw>
struct SelfReferenceIfNeeded {
Contained reference = nullptr;
};
template<typename Contained>
struct SelfReferenceIfNeeded<Contained, true> {
};
namespace Detail {
template<typename T, typename Container>
class IntrusiveListNode {
public:
~IntrusiveListNode();
void remove();
bool is_in_list() const;
static constexpr bool IsRaw = IsPointer<Container>;
// Note: For some reason, clang does not consider `member` as declared here, and as declared above (`IntrusiveListNode<T, Container> T::*`)
// to be of equal types. so for now, just make the members public on clang.
#ifndef __clang__
private:
template<class T_, typename Container_, IntrusiveListNode<T_, Container_> T_::*member>
friend class ::AK::IntrusiveList;
#endif
IntrusiveListStorage<T, Container>* m_storage = nullptr;
IntrusiveListNode<T, Container>* m_next = nullptr;
IntrusiveListNode<T, Container>* m_prev = nullptr;
[[no_unique_address]] SelfReferenceIfNeeded<Container, IsRaw> m_self;
};
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline typename IntrusiveList<T, Container, member>::Iterator& IntrusiveList<T, Container, member>::Iterator::erase()
{
auto old = m_value;
m_value = IntrusiveList<T, Container, member>::next(m_value);
(old->*member).remove();
return *this;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline IntrusiveList<T, Container, member>::~IntrusiveList()
{
clear();
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline void IntrusiveList<T, Container, member>::clear()
{
while (m_storage.m_first)
m_storage.m_first->remove();
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline bool IntrusiveList<T, Container, member>::is_empty() const
{
return m_storage.m_first == nullptr;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline size_t IntrusiveList<T, Container, member>::size_slow() const
{
size_t size = 0;
auto it_end = end();
for (auto it = begin(); it != it_end; ++it) {
++size;
}
return size;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline void IntrusiveList<T, Container, member>::append(T& n)
{
remove(n);
auto& nnode = n.*member;
nnode.m_storage = &m_storage;
nnode.m_prev = m_storage.m_last;
nnode.m_next = nullptr;
if constexpr (!RemoveReference<decltype(nnode)>::IsRaw)
nnode.m_self.reference = &n; // Note: Self-reference ensures that the object will keep a ref to itself when the Container is a smart pointer.
if (m_storage.m_last)
m_storage.m_last->m_next = &nnode;
m_storage.m_last = &nnode;
if (!m_storage.m_first)
m_storage.m_first = &nnode;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline void IntrusiveList<T, Container, member>::prepend(T& n)
{
remove(n);
auto& nnode = n.*member;
nnode.m_storage = &m_storage;
nnode.m_prev = nullptr;
nnode.m_next = m_storage.m_first;
if constexpr (!RemoveReference<decltype(nnode)>::IsRaw)
nnode.m_self.reference = &n;
if (m_storage.m_first)
m_storage.m_first->m_prev = &nnode;
m_storage.m_first = &nnode;
if (!m_storage.m_last)
m_storage.m_last = &nnode;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline void IntrusiveList<T, Container, member>::insert_before(T& bn, T& n)
{
remove(n);
auto& new_node = n.*member;
auto& before_node = bn.*member;
new_node.m_storage = &m_storage;
new_node.m_next = &before_node;
new_node.m_prev = before_node.m_prev;
if (before_node.m_prev)
before_node.m_prev->m_next = &new_node;
before_node.m_prev = &new_node;
if (m_storage.m_first == &before_node) {
m_storage.m_first = &new_node;
}
if constexpr (!RemoveReference<decltype(new_node)>::IsRaw)
new_node.m_self.reference = &n;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline void IntrusiveList<T, Container, member>::remove(T& n)
{
auto& nnode = n.*member;
if (nnode.m_storage)
nnode.remove();
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline bool IntrusiveList<T, Container, member>::contains(const T& n) const
{
auto& nnode = n.*member;
return nnode.m_storage == &m_storage;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline Container IntrusiveList<T, Container, member>::first() const
{
return m_storage.m_first ? node_to_value(*m_storage.m_first) : nullptr;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline Container IntrusiveList<T, Container, member>::take_first()
{
if (Container ptr = first()) {
remove(*ptr);
return ptr;
}
return nullptr;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline Container IntrusiveList<T, Container, member>::take_last()
{
if (Container ptr = last()) {
remove(*ptr);
return ptr;
}
return nullptr;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline Container IntrusiveList<T, Container, member>::last() const
{
return m_storage.m_last ? node_to_value(*m_storage.m_last) : nullptr;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline const T* IntrusiveList<T, Container, member>::next(const T* current)
{
auto& nextnode = (current->*member).m_next;
const T* nextstruct = nextnode ? node_to_value(*nextnode) : nullptr;
return nextstruct;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline const T* IntrusiveList<T, Container, member>::prev(const T* current)
{
auto& prevnode = (current->*member).m_prev;
const T* prevstruct = prevnode ? node_to_value(*prevnode) : nullptr;
return prevstruct;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline T* IntrusiveList<T, Container, member>::next(T* current)
{
auto& nextnode = (current->*member).m_next;
T* nextstruct = nextnode ? node_to_value(*nextnode) : nullptr;
return nextstruct;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline T* IntrusiveList<T, Container, member>::prev(T* current)
{
auto& prevnode = (current->*member).m_prev;
T* prevstruct = prevnode ? node_to_value(*prevnode) : nullptr;
return prevstruct;
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline typename IntrusiveList<T, Container, member>::Iterator IntrusiveList<T, Container, member>::begin()
{
return m_storage.m_first ? Iterator(node_to_value(*m_storage.m_first)) : Iterator();
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline typename IntrusiveList<T, Container, member>::ReverseIterator IntrusiveList<T, Container, member>::rbegin()
{
return m_storage.m_last ? ReverseIterator(node_to_value(*m_storage.m_last)) : ReverseIterator();
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline typename IntrusiveList<T, Container, member>::ConstIterator IntrusiveList<T, Container, member>::begin() const
{
return m_storage.m_first ? ConstIterator(node_to_value(*m_storage.m_first)) : ConstIterator();
}
template<class T, typename Container, IntrusiveListNode<T, Container> T::*member>
inline T* IntrusiveList<T, Container, member>::node_to_value(IntrusiveListNode<T, Container>& node)
{
// Note: Since this might seem odd, here's an explanation on what this function actually does:
// `node` is a reference that resides in some part of the actual value (of type T), the
// placement (i.e. offset) of which is described by the pointer-to-data-member parameter
// named `member`.
// This function effectively takes in the address of the data member, and returns the address
// of the value (of type T) holding that member.
return bit_cast<T*>(bit_cast<unsigned char*>(&node) - bit_cast<unsigned char*>(member));
}
namespace Detail {
template<typename T, typename Container>
inline IntrusiveListNode<T, Container>::~IntrusiveListNode()
{
VERIFY(!is_in_list());
}
template<typename T, typename Container>
inline void IntrusiveListNode<T, Container>::remove()
{
VERIFY(m_storage);
if (m_storage->m_first == this)
m_storage->m_first = m_next;
if (m_storage->m_last == this)
m_storage->m_last = m_prev;
if (m_prev)
m_prev->m_next = m_next;
if (m_next)
m_next->m_prev = m_prev;
m_prev = nullptr;
m_next = nullptr;
m_storage = nullptr;
if constexpr (!IsRaw)
m_self.reference = nullptr;
}
template<typename T, typename Container>
inline bool IntrusiveListNode<T, Container>::is_in_list() const
{
return m_storage != nullptr;
}
}
// Specialise IntrusiveList for NonnullRefPtr
// By default, intrusive lists cannot contain null entries anyway, so switch to RefPtr
// and just make the user-facing functions deref the pointers.
template<class T, IntrusiveListNode<T, NonnullRefPtr<T>> T::*member>
class IntrusiveList<T, NonnullRefPtr<T>, member> : public IntrusiveList<T, RefPtr<T>, member> {
public:
[[nodiscard]] NonnullRefPtr<T> first() const { return *IntrusiveList<T, RefPtr<T>, member>::first(); }
[[nodiscard]] NonnullRefPtr<T> last() const { return *IntrusiveList<T, RefPtr<T>, member>::last(); }
[[nodiscard]] NonnullRefPtr<T> take_first() { return *IntrusiveList<T, RefPtr<T>, member>::take_first(); }
[[nodiscard]] NonnullRefPtr<T> take_last() { return *IntrusiveList<T, RefPtr<T>, member>::take_last(); }
};
}
using AK::IntrusiveList;
using AK::IntrusiveListNode;