| // Copyright (c) 2009 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| // This file is a copy of Chromium's /src/base/containers/linked_list.h with the following |
| // modifications: |
| // - Added iterators for ranged based iterations |
| // - Added in list check before removing node to prevent segfault, now returns true iff removed |
| // - Added MoveInto functionality for moving list elements to another list |
| |
| #ifndef SRC_DAWN_COMMON_LINKEDLIST_H_ |
| #define SRC_DAWN_COMMON_LINKEDLIST_H_ |
| |
| #include "dawn/common/Assert.h" |
| |
| namespace dawn { |
| |
| // Simple LinkedList type. (See the Q&A section to understand how this |
| // differs from std::list). |
| // |
| // To use, start by declaring the class which will be contained in the linked |
| // list, as extending LinkNode (this gives it next/previous pointers). |
| // |
| // class MyNodeType : public LinkNode<MyNodeType> { |
| // ... |
| // }; |
| // |
| // Next, to keep track of the list's head/tail, use a LinkedList instance: |
| // |
| // LinkedList<MyNodeType> list; |
| // |
| // To add elements to the list, use any of LinkedList::Append, |
| // LinkNode::InsertBefore, or LinkNode::InsertAfter: |
| // |
| // LinkNode<MyNodeType>* n1 = ...; |
| // LinkNode<MyNodeType>* n2 = ...; |
| // LinkNode<MyNodeType>* n3 = ...; |
| // |
| // list.Append(n1); |
| // list.Append(n3); |
| // n3->InsertBefore(n3); |
| // |
| // Lastly, to iterate through the linked list forwards: |
| // |
| // for (LinkNode<MyNodeType>* node = list.head(); |
| // node != list.end(); |
| // node = node->next()) { |
| // MyNodeType* value = node->value(); |
| // ... |
| // } |
| // |
| // for (LinkNode<MyNodeType*> node : list) { |
| // MyNodeType* value = node->value(); |
| // ... |
| // } |
| // |
| // Or to iterate the linked list backwards: |
| // |
| // for (LinkNode<MyNodeType>* node = list.tail(); |
| // node != list.end(); |
| // node = node->previous()) { |
| // MyNodeType* value = node->value(); |
| // ... |
| // } |
| // |
| // Questions and Answers: |
| // |
| // Q. Should I use std::list or base::LinkedList? |
| // |
| // A. The main reason to use base::LinkedList over std::list is |
| // performance. If you don't care about the performance differences |
| // then use an STL container, as it makes for better code readability. |
| // |
| // Comparing the performance of base::LinkedList<T> to std::list<T*>: |
| // |
| // * Erasing an element of type T* from base::LinkedList<T> is |
| // an O(1) operation. Whereas for std::list<T*> it is O(n). |
| // That is because with std::list<T*> you must obtain an |
| // iterator to the T* element before you can call erase(iterator). |
| // |
| // * Insertion operations with base::LinkedList<T> never require |
| // heap allocations. |
| // |
| // Q. How does base::LinkedList implementation differ from std::list? |
| // |
| // A. Doubly-linked lists are made up of nodes that contain "next" and |
| // "previous" pointers that reference other nodes in the list. |
| // |
| // With base::LinkedList<T>, the type being inserted already reserves |
| // space for the "next" and "previous" pointers (base::LinkNode<T>*). |
| // Whereas with std::list<T> the type can be anything, so the implementation |
| // needs to glue on the "next" and "previous" pointers using |
| // some internal node type. |
| |
| // Forward declarations of the types in order for recursive referencing and friending. |
| template <typename T> |
| class LinkNode; |
| template <typename T> |
| class LinkedList; |
| |
| template <typename T> |
| class LinkNode { |
| public: |
| LinkNode() : previous_(nullptr), next_(nullptr) {} |
| LinkNode(LinkNode<T>* previous, LinkNode<T>* next) : previous_(previous), next_(next) {} |
| |
| LinkNode(LinkNode<T>&& rhs) { |
| next_ = rhs.next_; |
| rhs.next_ = nullptr; |
| previous_ = rhs.previous_; |
| rhs.previous_ = nullptr; |
| |
| // If the node belongs to a list, next_ and previous_ are both non-null. |
| // Otherwise, they are both null. |
| if (next_) { |
| next_->previous_ = this; |
| previous_->next_ = this; |
| } |
| } |
| |
| ~LinkNode() { |
| // Remove the node from any list, otherwise there can be outstanding references to the node |
| // even after it has been freed. |
| RemoveFromList(); |
| } |
| |
| // Insert |this| into the linked list, before |e|. |
| void InsertBefore(LinkNode<T>* e) { |
| this->next_ = e; |
| this->previous_ = e->previous_; |
| e->previous_->next_ = this; |
| e->previous_ = this; |
| } |
| |
| // Insert |this| into the linked list, after |e|. |
| void InsertAfter(LinkNode<T>* e) { |
| this->next_ = e->next_; |
| this->previous_ = e; |
| e->next_->previous_ = this; |
| e->next_ = this; |
| } |
| |
| // Check if |this| is in a list. |
| bool IsInList() const { |
| ASSERT((this->previous_ == nullptr) == (this->next_ == nullptr)); |
| return this->next_ != nullptr; |
| } |
| |
| // Remove |this| from the linked list. Returns true iff removed from a list. |
| bool RemoveFromList() { |
| if (!IsInList()) { |
| return false; |
| } |
| |
| this->previous_->next_ = this->next_; |
| this->next_->previous_ = this->previous_; |
| // next() and previous() return non-null if and only this node is not in any list. |
| this->next_ = nullptr; |
| this->previous_ = nullptr; |
| return true; |
| } |
| |
| LinkNode<T>* previous() const { return previous_; } |
| |
| LinkNode<T>* next() const { return next_; } |
| |
| // Cast from the node-type to the value type. |
| const T* value() const { return static_cast<const T*>(this); } |
| |
| T* value() { return static_cast<T*>(this); } |
| |
| private: |
| friend class LinkedList<T>; |
| LinkNode<T>* previous_; |
| LinkNode<T>* next_; |
| }; |
| |
| template <typename T> |
| class LinkedList { |
| public: |
| // The "root" node is self-referential, and forms the basis of a circular |
| // list (root_.next() will point back to the start of the list, |
| // and root_->previous() wraps around to the end of the list). |
| LinkedList() : root_(&root_, &root_) {} |
| |
| // Appends |e| to the end of the linked list. |
| void Append(LinkNode<T>* e) { e->InsertBefore(&root_); } |
| |
| // Prepends |e| to the front og the linked list. |
| void Prepend(LinkNode<T>* e) { e->InsertAfter(&root_); } |
| |
| // Moves all elements (in order) of the list and appends them into |l| leaving the list empty. |
| void MoveInto(LinkedList<T>* l) { |
| if (empty()) { |
| return; |
| } |
| l->root_.previous_->next_ = root_.next_; |
| root_.next_->previous_ = l->root_.previous_; |
| l->root_.previous_ = root_.previous_; |
| root_.previous_->next_ = &l->root_; |
| |
| root_.next_ = &root_; |
| root_.previous_ = &root_; |
| } |
| |
| LinkNode<T>* head() const { return root_.next(); } |
| |
| LinkNode<T>* tail() const { return root_.previous(); } |
| |
| const LinkNode<T>* end() const { return &root_; } |
| |
| bool empty() const { return head() == end(); } |
| |
| private: |
| LinkNode<T> root_; |
| }; |
| |
| template <typename T> |
| class LinkedListIterator { |
| public: |
| explicit LinkedListIterator(LinkNode<T>* node) : current_(node), next_(node->next()) {} |
| |
| // We keep an early reference to the next node in the list so that even if the current element |
| // is modified or removed from the list, we have a valid next node. |
| LinkedListIterator<T> const& operator++() { |
| current_ = next_; |
| next_ = current_->next(); |
| return *this; |
| } |
| |
| bool operator!=(const LinkedListIterator<T>& other) const { return current_ != other.current_; } |
| |
| LinkNode<T>* operator*() const { return current_; } |
| |
| private: |
| LinkNode<T>* current_; |
| LinkNode<T>* next_; |
| }; |
| |
| template <typename T> |
| LinkedListIterator<T> begin(LinkedList<T>& l) { |
| return LinkedListIterator<T>(l.head()); |
| } |
| |
| // Free end function does't use LinkedList<T>::end because of it's const nature. Instead we wrap |
| // around from tail. |
| template <typename T> |
| LinkedListIterator<T> end(LinkedList<T>& l) { |
| return LinkedListIterator<T>(l.tail()->next()); |
| } |
| |
| } // namespace dawn |
| |
| #endif // SRC_DAWN_COMMON_LINKEDLIST_H_ |