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Bug 715405 - Add a type-safe linked list class. r=waldo

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--HG--
extra : rebase_source : c1a829b9c1264c6b07a10b1ff7a8d0a64e3125f7
This commit is contained in:
Justin Lebar 2012-01-26 15:54:03 -05:00
parent 09e70c8a76
commit fc0cb053c5
2 changed files with 401 additions and 0 deletions
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400
mfbt/LinkedList.h Normal file
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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: set ts=4 sw=4 tw=80 et cin:
*
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (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.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla Code.
*
* The Initial Developer of the Original Code is
* The Mozilla Foundation
* Portions created by the Initial Developer are Copyright (C) 2012
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Justin Lebar <justin.lebar@gmail.com>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
/* 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.
*
* For example, you might use LinkedList in a simple observer list class as
* follows.
*
* class Observer : public LinkedListElement<Observer>
* {
* void observe(char* topic) { ... }
* };
*
* class ObserverContainer
* {
* private:
* LinkedList<ElemType> 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();
* }
*
* 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.
*/
private:
LinkedListElement* next;
LinkedListElement* prev;
const bool isSentinel;
public:
LinkedListElement()
: next(this)
, prev(this)
, isSentinel(false)
{
}
/*
* Get the next element in the list, or NULL if this is the last element in
* the list.
*/
T* getNext()
{
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();
}
/*
* 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;
}
/*
* Return true if |this| part is of a linked list, and false otherwise.
*/
bool isInList()
{
MOZ_ASSERT((next == this) == (prev == this));
return next != this;
}
private:
LinkedListElement& operator=(const LinkedList<T>& other) MOZ_DELETE;
LinkedListElement(const LinkedList<T>& other) MOZ_DELETE;
friend class LinkedList<T>;
enum NodeKind {
NODE_TYPE_NORMAL,
NODE_TYPE_SENTINEL
};
LinkedListElement(NodeKind nodeType)
: next(this)
, prev(this)
, isSentinel(nodeType == NODE_TYPE_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);
}
/*
* 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;
}
};
template<typename T>
class LinkedList
{
private:
LinkedListElement<T> sentinel;
public:
LinkedList& operator=(const LinkedList<T>& other) MOZ_DELETE;
LinkedList(const LinkedList<T>& other) MOZ_DELETE;
LinkedList()
: sentinel(LinkedListElement<T>::NODE_TYPE_SENTINEL)
{
}
/*
* 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();
}
/*
* Get the last element of the list, or NULL if the list is empty.
*/
T* getLast()
{
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()
{
return !sentinel.isInList();
}
/*
* 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()
{
#ifdef DEBUG
/*
* Check for cycles in the forward singly-linked list using the
* tortoise/hare algorithm.
*/
for (LinkedListElement<T>* 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 (LinkedListElement<T>* 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 root in the list. */
for (LinkedListElement<T>* elem = sentinel.next;
elem != sentinel;
elem = elem->next) {
MOZ_ASSERT(!elem->isSentinel);
}
/* Check that the next/prev pointers match up. */
LinkedListElement<T>* prev = sentinel;
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 */
}
};
} /* namespace mozilla */
#endif /* ifdef __cplusplus */
#endif /* ifdef mozilla_LinkedList_h_ */

1
mfbt/exported_headers.mk
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@ -45,6 +45,7 @@ EXPORTS_mozilla += \
Assertions.h \
Attributes.h \
GuardObjects.h \
LinkedList.h \
MSStdInt.h \
RangedPtr.h \
RefPtr.h \