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This file is part of the KDE libraries
Copyright (C) 1998 Lars Knoll (
Copyright (C) 2001 Dirk Mueller <>
Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
Library General Public License for more details.
You should have received a copy of the GNU Library General Public License
along with this library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA.
This class provides all functionality needed for loading images, style sheets and html
pages from the web. It has a memory cache for these objects.
#ifndef Cache_h
#define Cache_h
#include "CachePolicy.h"
#include "CachedResource.h"
#include "PlatformString.h"
#include "StringHash.h"
#include "loader.h"
#include <wtf/HashMap.h>
#include <wtf/HashSet.h>
#include <wtf/Noncopyable.h>
#include <wtf/Vector.h>
namespace WebCore {
class CachedResource;
class DocLoader;
class KURL;
// This cache holds subresources used by Web pages: images, scripts, stylesheets, etc.
// The cache keeps a flexible but bounded window of dead resources that grows/shrinks
// depending on the live resource load. Here's an example of cache growth over time,
// with a min dead resource capacity of 25% and a max dead resource capacity of 50%:
// |-----| Dead: -
// |----------| Live: +
// --|----------| Cache boundary: | (objects outside this mark have been evicted)
// --|----------++++++++++|
// -------|-----+++++++++++++++|
// -------|-----+++++++++++++++|+++++
class Cache : Noncopyable {
friend Cache* cache();
typedef HashMap<String, CachedResource*> CachedResourceMap;
struct LRUList {
CachedResource* m_head;
CachedResource* m_tail;
LRUList() : m_head(0), m_tail(0) { }
struct TypeStatistic {
int count;
int size;
int liveSize;
int decodedSize;
TypeStatistic() : count(0), size(0), liveSize(0), decodedSize(0) { }
struct Statistics {
TypeStatistic images;
TypeStatistic cssStyleSheets;
TypeStatistic scripts;
TypeStatistic xslStyleSheets;
TypeStatistic xblDocs;
TypeStatistic fonts;
// The loader that fetches resources.
Loader* loader() { return &m_loader; }
// Request resources from the cache. A load will be initiated and a cache object created if the object is not
// found in the cache.
CachedResource* requestResource(DocLoader*, CachedResource::Type, const KURL& url, const String* charset = 0, bool skipCanLoadCheck = false, bool sendResourceLoadCallbacks = true);
// Sets the cache's memory capacities, in bytes. These will hold only approximately,
// since the decoded cost of resources like scripts and stylesheets is not known.
// - minDeadBytes: The maximum number of bytes that dead resources should consume when the cache is under pressure.
// - maxDeadBytes: The maximum number of bytes that dead resources should consume when the cache is not under pressure.
// - totalBytes: The maximum number of bytes that the cache should consume overall.
void setCapacities(unsigned minDeadBytes, unsigned maxDeadBytes, unsigned totalBytes);
// Turn the cache on and off. Disabling the cache will remove all resources from the cache. They may
// still live on if they are referenced by some Web page though.
void setDisabled(bool);
bool disabled() const { return m_disabled; }
void setPruneEnabled(bool enabled) { m_pruneEnabled = enabled; }
void prune()
if (m_liveSize + m_deadSize <= m_capacity && m_deadSize <= m_maxDeadCapacity) // Fast path.
pruneDeadResources(); // Prune dead first, in case it was "borrowing" capacity from live.
// Remove an existing cache entry from both the resource map and from the LRU list.
void remove(CachedResource*);
void addDocLoader(DocLoader*);
void removeDocLoader(DocLoader*);
CachedResource* resourceForURL(const String&);
// Calls to put the cached resource into and out of LRU lists.
void insertInLRUList(CachedResource*);
void removeFromLRUList(CachedResource*);
// Called to adjust the cache totals when a resource changes size.
void adjustSize(bool live, int delta);
// Track decoded resources that are in the cache and referenced by a Web page.
void insertInLiveDecodedResourcesList(CachedResource*);
void removeFromLiveDecodedResourcesList(CachedResource*);
void addToLiveResourcesSize(CachedResource*);
void removeFromLiveResourcesSize(CachedResource*);
// Function to collect cache statistics for the caches window in the Safari Debug menu.
Statistics getStatistics();
~Cache(); // Not implemented to make sure nobody accidentally calls delete -- WebCore does not delete singletons.
LRUList* lruListFor(CachedResource*);
void resourceAccessed(CachedResource*);
#ifndef NDEBUG
void dumpLRULists(bool includeLive) const;
unsigned liveCapacity() const;
unsigned deadCapacity() const;
void pruneDeadResources(); // Flush decoded and encoded data from resources not referenced by Web pages.
void pruneLiveResources(); // Flush decoded data from resources still referenced by Web pages.
// Member variables.
HashSet<DocLoader*> m_docLoaders;
Loader m_loader;
bool m_disabled; // Whether or not the cache is enabled.
bool m_pruneEnabled;
unsigned m_capacity;
unsigned m_minDeadCapacity;
unsigned m_maxDeadCapacity;
unsigned m_liveSize; // The number of bytes currently consumed by "live" resources in the cache.
unsigned m_deadSize; // The number of bytes currently consumed by "dead" resources in the cache.
// Size-adjusted and popularity-aware LRU list collection for cache objects. This collection can hold
// more resources than the cached resource map, since it can also hold "stale" muiltiple versions of objects that are
// waiting to die when the clients referencing them go away.
Vector<LRUList, 32> m_allResources;
// List just for live resources with decoded data. Access to this list is based off of painting the resource.
LRUList m_liveDecodedResources;
// A URL-based map of all resources that are in the cache (including the freshest version of objects that are currently being
// referenced by a Web page).
HashMap<String, CachedResource*> m_resources;
// Function to obtain the global cache.
Cache* cache();