mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-05 08:35:26 +00:00
430 lines
12 KiB
C++
430 lines
12 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
|
|
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
/* A type-safe doubly-linked list class. */
|
|
|
|
/*
|
|
* The classes LinkedList<T> and LinkedListElement<T> together form a
|
|
* convenient, type-safe doubly-linked list implementation.
|
|
*
|
|
* The class T which will be inserted into the linked list must inherit from
|
|
* LinkedListElement<T>. A given object may be in only one linked list at a
|
|
* time.
|
|
*
|
|
* A LinkedListElement automatically removes itself from the list upon
|
|
* destruction, and a LinkedList will fatally assert in debug builds if it's
|
|
* non-empty when it's destructed.
|
|
*
|
|
* For example, you might use LinkedList in a simple observer list class as
|
|
* follows.
|
|
*
|
|
* class Observer : public LinkedListElement<Observer>
|
|
* {
|
|
* public:
|
|
* void observe(char* topic) { ... }
|
|
* };
|
|
*
|
|
* class ObserverContainer
|
|
* {
|
|
* private:
|
|
* LinkedList<Observer> list;
|
|
*
|
|
* public:
|
|
* void addObserver(Observer* observer) {
|
|
* // Will assert if |observer| is part of another list.
|
|
* list.insertBack(observer);
|
|
* }
|
|
*
|
|
* void removeObserver(Observer* observer) {
|
|
* // Will assert if |observer| is not part of some list.
|
|
* observer.remove();
|
|
* // Or, will assert if |observer| is not part of |list| specifically.
|
|
* // observer.removeFrom(list);
|
|
* }
|
|
*
|
|
* void notifyObservers(char* topic) {
|
|
* for (Observer* o = list.getFirst(); o != NULL; o = o->getNext())
|
|
* o->Observe(topic);
|
|
* }
|
|
* };
|
|
*
|
|
*/
|
|
|
|
#ifndef mozilla_LinkedList_h_
|
|
#define mozilla_LinkedList_h_
|
|
|
|
#include "mozilla/Assertions.h"
|
|
#include "mozilla/Attributes.h"
|
|
|
|
#ifdef __cplusplus
|
|
|
|
namespace mozilla {
|
|
|
|
template<typename T>
|
|
class LinkedList;
|
|
|
|
template<typename T>
|
|
class LinkedListElement
|
|
{
|
|
/*
|
|
* It's convenient that we return NULL when getNext() or getPrevious() hits
|
|
* the end of the list, but doing so costs an extra word of storage in each
|
|
* linked list node (to keep track of whether |this| is the sentinel node)
|
|
* and a branch on this value in getNext/getPrevious.
|
|
*
|
|
* We could get rid of the extra word of storage by shoving the "is
|
|
* sentinel" bit into one of the pointers, although this would, of course,
|
|
* have performance implications of its own.
|
|
*
|
|
* But the goal here isn't to win an award for the fastest or slimmest
|
|
* linked list; rather, we want a *convenient* linked list. So we won't
|
|
* waste time guessing which micro-optimization strategy is best.
|
|
*
|
|
*
|
|
* Speaking of unnecessary work, it's worth addressing here why we wrote
|
|
* mozilla::LinkedList in the first place, instead of using stl::list.
|
|
*
|
|
* The key difference between mozilla::LinkedList and stl::list is that
|
|
* mozilla::LinkedList stores the prev/next pointers in the object itself,
|
|
* while stl::list stores the prev/next pointers in a list element which
|
|
* itself points to the object being stored.
|
|
*
|
|
* mozilla::LinkedList's approach makes it harder to store an object in more
|
|
* than one list. But the upside is that you can call next() / prev() /
|
|
* remove() directly on the object. With stl::list, you'd need to store a
|
|
* pointer to its iterator in the object in order to accomplish this. Not
|
|
* only would this waste space, but you'd have to remember to update that
|
|
* pointer every time you added or removed the object from a list.
|
|
*
|
|
* In-place, constant-time removal is a killer feature of doubly-linked
|
|
* lists, and supporting this painlessly was a key design criterion.
|
|
*/
|
|
|
|
private:
|
|
LinkedListElement* next;
|
|
LinkedListElement* prev;
|
|
const bool isSentinel;
|
|
|
|
LinkedListElement* thisDuringConstruction() { return this; }
|
|
|
|
public:
|
|
LinkedListElement()
|
|
: next(thisDuringConstruction()),
|
|
prev(thisDuringConstruction()),
|
|
isSentinel(false)
|
|
{ }
|
|
|
|
~LinkedListElement() {
|
|
if (!isSentinel && isInList())
|
|
remove();
|
|
}
|
|
|
|
/*
|
|
* Get the next element in the list, or NULL if this is the last element in
|
|
* the list.
|
|
*/
|
|
T* getNext() {
|
|
return next->asT();
|
|
}
|
|
const T* getNext() const {
|
|
return next->asT();
|
|
}
|
|
|
|
/*
|
|
* Get the previous element in the list, or NULL if this is the first element
|
|
* in the list.
|
|
*/
|
|
T* getPrevious() {
|
|
return prev->asT();
|
|
}
|
|
const T* getPrevious() const {
|
|
return prev->asT();
|
|
}
|
|
|
|
/*
|
|
* Insert elem after this element in the list. |this| must be part of a
|
|
* linked list when you call setNext(); otherwise, this method will assert.
|
|
*/
|
|
void setNext(T* elem) {
|
|
MOZ_ASSERT(isInList());
|
|
setNextUnsafe(elem);
|
|
}
|
|
|
|
/*
|
|
* Insert elem before this element in the list. |this| must be part of a
|
|
* linked list when you call setPrevious(); otherwise, this method will
|
|
* assert.
|
|
*/
|
|
void setPrevious(T* elem) {
|
|
MOZ_ASSERT(isInList());
|
|
setPreviousUnsafe(elem);
|
|
}
|
|
|
|
/*
|
|
* Remove this element from the list which contains it. If this element is
|
|
* not currently part of a linked list, this method asserts.
|
|
*/
|
|
void remove() {
|
|
MOZ_ASSERT(isInList());
|
|
|
|
prev->next = next;
|
|
next->prev = prev;
|
|
next = this;
|
|
prev = this;
|
|
}
|
|
|
|
/*
|
|
* Identical to remove(), but also asserts in debug builds that this element
|
|
* is in list.
|
|
*/
|
|
void removeFrom(const LinkedList<T>& list) {
|
|
list.assertContains(asT());
|
|
remove();
|
|
}
|
|
|
|
/*
|
|
* Return true if |this| part is of a linked list, and false otherwise.
|
|
*/
|
|
bool isInList() const {
|
|
MOZ_ASSERT((next == this) == (prev == this));
|
|
return next != this;
|
|
}
|
|
|
|
private:
|
|
friend class LinkedList<T>;
|
|
|
|
enum NodeKind {
|
|
NODE_KIND_NORMAL,
|
|
NODE_KIND_SENTINEL
|
|
};
|
|
|
|
LinkedListElement(NodeKind nodeKind)
|
|
: next(thisDuringConstruction()),
|
|
prev(thisDuringConstruction()),
|
|
isSentinel(nodeKind == NODE_KIND_SENTINEL)
|
|
{ }
|
|
|
|
/*
|
|
* Return |this| cast to T* if we're a normal node, or return NULL if we're
|
|
* a sentinel node.
|
|
*/
|
|
T* asT() {
|
|
if (isSentinel)
|
|
return NULL;
|
|
|
|
return static_cast<T*>(this);
|
|
}
|
|
const T* asT() const {
|
|
if (isSentinel)
|
|
return NULL;
|
|
|
|
return static_cast<const T*>(this);
|
|
}
|
|
|
|
/*
|
|
* Insert elem after this element, but don't check that this element is in
|
|
* the list. This is called by LinkedList::insertFront().
|
|
*/
|
|
void setNextUnsafe(T* elem) {
|
|
LinkedListElement *listElem = static_cast<LinkedListElement*>(elem);
|
|
MOZ_ASSERT(!listElem->isInList());
|
|
|
|
listElem->next = this->next;
|
|
listElem->prev = this;
|
|
this->next->prev = listElem;
|
|
this->next = listElem;
|
|
}
|
|
|
|
/*
|
|
* Insert elem before this element, but don't check that this element is in
|
|
* the list. This is called by LinkedList::insertBack().
|
|
*/
|
|
void setPreviousUnsafe(T* elem) {
|
|
LinkedListElement<T>* listElem = static_cast<LinkedListElement<T>*>(elem);
|
|
MOZ_ASSERT(!listElem->isInList());
|
|
|
|
listElem->next = this;
|
|
listElem->prev = this->prev;
|
|
this->prev->next = listElem;
|
|
this->prev = listElem;
|
|
}
|
|
|
|
private:
|
|
LinkedListElement& operator=(const LinkedList<T>& other) MOZ_DELETE;
|
|
LinkedListElement(const LinkedList<T>& other) MOZ_DELETE;
|
|
};
|
|
|
|
template<typename T>
|
|
class LinkedList
|
|
{
|
|
private:
|
|
LinkedListElement<T> sentinel;
|
|
|
|
public:
|
|
LinkedList() : sentinel(LinkedListElement<T>::NODE_KIND_SENTINEL) { }
|
|
|
|
~LinkedList() {
|
|
MOZ_ASSERT(isEmpty());
|
|
}
|
|
|
|
/*
|
|
* Add elem to the front of the list.
|
|
*/
|
|
void insertFront(T* elem) {
|
|
/* Bypass setNext()'s this->isInList() assertion. */
|
|
sentinel.setNextUnsafe(elem);
|
|
}
|
|
|
|
/*
|
|
* Add elem to the back of the list.
|
|
*/
|
|
void insertBack(T* elem) {
|
|
sentinel.setPreviousUnsafe(elem);
|
|
}
|
|
|
|
/*
|
|
* Get the first element of the list, or NULL if the list is empty.
|
|
*/
|
|
T* getFirst() {
|
|
return sentinel.getNext();
|
|
}
|
|
const T* getFirst() const {
|
|
return sentinel.getNext();
|
|
}
|
|
|
|
/*
|
|
* Get the last element of the list, or NULL if the list is empty.
|
|
*/
|
|
T* getLast() {
|
|
return sentinel.getPrevious();
|
|
}
|
|
const T* getLast() const {
|
|
return sentinel.getPrevious();
|
|
}
|
|
|
|
/*
|
|
* Get and remove the first element of the list. If the list is empty,
|
|
* return NULL.
|
|
*/
|
|
T* popFirst() {
|
|
T* ret = sentinel.getNext();
|
|
if (ret)
|
|
static_cast<LinkedListElement<T>*>(ret)->remove();
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Get and remove the last element of the list. If the list is empty,
|
|
* return NULL.
|
|
*/
|
|
T* popLast() {
|
|
T* ret = sentinel.getPrevious();
|
|
if (ret)
|
|
static_cast<LinkedListElement<T>*>(ret)->remove();
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Return true if the list is empty, or false otherwise.
|
|
*/
|
|
bool isEmpty() const {
|
|
return !sentinel.isInList();
|
|
}
|
|
|
|
/*
|
|
* Remove all the elements from the list.
|
|
*
|
|
* This runs in time linear to the list's length, because we have to mark
|
|
* each element as not in the list.
|
|
*/
|
|
void clear() {
|
|
while (popFirst())
|
|
continue;
|
|
}
|
|
|
|
/*
|
|
* In a debug build, make sure that the list is sane (no cycles, consistent
|
|
* next/prev pointers, only one sentinel). Has no effect in release builds.
|
|
*/
|
|
void debugAssertIsSane() const {
|
|
#ifdef DEBUG
|
|
const LinkedListElement<T>* slow;
|
|
const LinkedListElement<T>* fast1;
|
|
const LinkedListElement<T>* fast2;
|
|
|
|
/*
|
|
* Check for cycles in the forward singly-linked list using the
|
|
* tortoise/hare algorithm.
|
|
*/
|
|
for (slow = sentinel.next,
|
|
fast1 = sentinel.next->next,
|
|
fast2 = sentinel.next->next->next;
|
|
slow != sentinel && fast1 != sentinel && fast2 != sentinel;
|
|
slow = slow->next, fast1 = fast2->next, fast2 = fast1->next)
|
|
{
|
|
MOZ_ASSERT(slow != fast1);
|
|
MOZ_ASSERT(slow != fast2);
|
|
}
|
|
|
|
/* Check for cycles in the backward singly-linked list. */
|
|
for (slow = sentinel.prev,
|
|
fast1 = sentinel.prev->prev,
|
|
fast2 = sentinel.prev->prev->prev;
|
|
slow != sentinel && fast1 != sentinel && fast2 != sentinel;
|
|
slow = slow->prev, fast1 = fast2->prev, fast2 = fast1->prev)
|
|
{
|
|
MOZ_ASSERT(slow != fast1);
|
|
MOZ_ASSERT(slow != fast2);
|
|
}
|
|
|
|
/*
|
|
* Check that |sentinel| is the only node in the list with
|
|
* isSentinel == true.
|
|
*/
|
|
for (const LinkedListElement<T>* elem = sentinel.next;
|
|
elem != sentinel;
|
|
elem = elem->next)
|
|
{
|
|
MOZ_ASSERT(!elem->isSentinel);
|
|
}
|
|
|
|
/* Check that the next/prev pointers match up. */
|
|
const LinkedListElement<T>* prev = sentinel;
|
|
const LinkedListElement<T>* cur = sentinel.next;
|
|
do {
|
|
MOZ_ASSERT(cur->prev == prev);
|
|
MOZ_ASSERT(prev->next == cur);
|
|
|
|
prev = cur;
|
|
cur = cur->next;
|
|
} while (cur != sentinel);
|
|
#endif /* ifdef DEBUG */
|
|
}
|
|
|
|
private:
|
|
friend class LinkedListElement<T>;
|
|
|
|
void assertContains(const T* t) const {
|
|
#ifdef DEBUG
|
|
for (const T* elem = getFirst();
|
|
elem;
|
|
elem = elem->getNext())
|
|
{
|
|
if (elem == t)
|
|
return;
|
|
}
|
|
MOZ_NOT_REACHED("element wasn't found in this list!");
|
|
#endif
|
|
}
|
|
|
|
LinkedList& operator=(const LinkedList<T>& other) MOZ_DELETE;
|
|
LinkedList(const LinkedList<T>& other) MOZ_DELETE;
|
|
};
|
|
|
|
} /* namespace mozilla */
|
|
|
|
#endif /* ifdef __cplusplus */
|
|
#endif /* ifdef mozilla_LinkedList_h_ */
|