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* Copyright 2013 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkResourceCache_DEFINED
#define SkResourceCache_DEFINED
#include "include/core/SkBitmap.h"
#include "include/private/SkTDArray.h"
#include "src/core/SkMessageBus.h"
class SkCachedData;
class SkDiscardableMemory;
class SkTraceMemoryDump;
* Cache object for bitmaps (with possible scale in X Y as part of the key).
* Multiple caches can be instantiated, but each instance is not implicitly
* thread-safe, so if a given instance is to be shared across threads, the
* caller must manage the access itself (e.g. via a mutex).
* As a convenience, a global instance is also defined, which can be safely
* access across threads via the static methods (e.g. FindAndLock, etc.).
class SkResourceCache {
struct Key {
/** Key subclasses must call this after their own fields and data are initialized.
* All fields and data must be tightly packed.
* @param nameSpace must be unique per Key subclass.
* @param sharedID == 0 means ignore this field, does not support group purging.
* @param dataSize is size of fields and data of the subclass, must be a multiple of 4.
void init(void* nameSpace, uint64_t sharedID, size_t dataSize);
/** Returns the size of this key. */
size_t size() const {
return fCount32 << 2;
void* getNamespace() const { return fNamespace; }
uint64_t getSharedID() const { return ((uint64_t)fSharedID_hi << 32) | fSharedID_lo; }
// This is only valid after having called init().
uint32_t hash() const { return fHash; }
bool operator==(const Key& other) const {
const uint32_t* a = this->as32();
const uint32_t* b = other.as32();
for (int i = 0; i < fCount32; ++i) { // (This checks fCount == other.fCount first.)
if (a[i] != b[i]) {
return false;
return true;
int32_t fCount32; // local + user contents count32
uint32_t fHash;
// split uint64_t into hi and lo so we don't force ourselves to pad on 32bit machines.
uint32_t fSharedID_lo;
uint32_t fSharedID_hi;
void* fNamespace; // A unique namespace tag. This is hashed.
/* uint32_t fContents32[] */
const uint32_t* as32() const { return (const uint32_t*)this; }
struct Rec {
typedef SkResourceCache::Key Key;
Rec() {}
virtual ~Rec() {}
uint32_t getHash() const { return this->getKey().hash(); }
virtual const Key& getKey() const = 0;
virtual size_t bytesUsed() const = 0;
// Called if the cache needs to purge/remove/delete the Rec. Default returns true.
// Subclass may return false if there are outstanding references to it (e.g. bitmaps).
// Will only be deleted/removed-from-the-cache when this returns true.
virtual bool canBePurged() { return true; }
// A rec is first created/initialized, and then added to the cache. As part of the add(),
// the cache will callback into the rec with postAddInstall, passing in whatever payload
// was passed to add/Add.
// This late-install callback exists because the process of add-ing might end up deleting
// the new rec (if an existing rec in the cache has the same key and cannot be purged).
// If the new rec will be deleted during add, the pre-existing one (with the same key)
// will have postAddInstall() called on it instead, so that either way an "install" will
// happen during the add.
virtual void postAddInstall(void*) {}
// for memory usage diagnostics
virtual const char* getCategory() const = 0;
virtual SkDiscardableMemory* diagnostic_only_getDiscardable() const { return nullptr; }
Rec* fNext;
Rec* fPrev;
friend class SkResourceCache;
// Used with SkMessageBus
struct PurgeSharedIDMessage {
PurgeSharedIDMessage(uint64_t sharedID) : fSharedID(sharedID) {}
uint64_t fSharedID;
typedef const Rec* ID;
* Callback function for find(). If called, the cache will have found a match for the
* specified Key, and will pass in the corresponding Rec, along with a caller-specified
* context. The function can read the data in Rec, and copy whatever it likes into context
* (casting context to whatever it really is).
* The return value determines what the cache will do with the Rec. If the function returns
* true, then the Rec is considered "valid". If false is returned, the Rec will be considered
* "stale" and will be purged from the cache.
typedef bool (*FindVisitor)(const Rec&, void* context);
* Returns a locked/pinned SkDiscardableMemory instance for the specified
* number of bytes, or nullptr on failure.
typedef SkDiscardableMemory* (*DiscardableFactory)(size_t bytes);
* The following static methods are thread-safe wrappers around a global
* instance of this cache.
* Returns true if the visitor was called on a matching Key, and the visitor returned true.
* Find() will search the cache for the specified Key. If no match is found, return false and
* do not call the FindVisitor. If a match is found, return whatever the visitor returns.
* Its return value is interpreted to mean:
* true : Rec is valid
* false : Rec is "stale" -- the cache will purge it.
static bool Find(const Key& key, FindVisitor, void* context);
static void Add(Rec*, void* payload = nullptr);
typedef void (*Visitor)(const Rec&, void* context);
// Call the visitor for every Rec in the cache.
static void VisitAll(Visitor, void* context);
static size_t GetTotalBytesUsed();
static size_t GetTotalByteLimit();
static size_t SetTotalByteLimit(size_t newLimit);
static size_t SetSingleAllocationByteLimit(size_t);
static size_t GetSingleAllocationByteLimit();
static size_t GetEffectiveSingleAllocationByteLimit();
static void PurgeAll();
static void CheckMessages();
static void TestDumpMemoryStatistics();
/** Dump memory usage statistics of every Rec in the cache using the
SkTraceMemoryDump interface.
static void DumpMemoryStatistics(SkTraceMemoryDump* dump);
* Returns the DiscardableFactory used by the global cache, or nullptr.
static DiscardableFactory GetDiscardableFactory();
static SkCachedData* NewCachedData(size_t bytes);
static void PostPurgeSharedID(uint64_t sharedID);
* Call SkDebugf() with diagnostic information about the state of the cache
static void Dump();
* Construct the cache to call DiscardableFactory when it
* allocates memory for the pixels. In this mode, the cache has
* not explicit budget, and so methods like getTotalBytesUsed()
* and getTotalByteLimit() will return 0, and setTotalByteLimit
* will ignore its argument and return 0.
* Construct the cache, allocating memory with malloc, and respect the
* byteLimit, purging automatically when a new image is added to the cache
* that pushes the total bytesUsed over the limit. Note: The limit can be
* changed at runtime with setTotalByteLimit.
explicit SkResourceCache(size_t byteLimit);
* Returns true if the visitor was called on a matching Key, and the visitor returned true.
* find() will search the cache for the specified Key. If no match is found, return false and
* do not call the FindVisitor. If a match is found, return whatever the visitor returns.
* Its return value is interpreted to mean:
* true : Rec is valid
* false : Rec is "stale" -- the cache will purge it.
bool find(const Key&, FindVisitor, void* context);
void add(Rec*, void* payload = nullptr);
void visitAll(Visitor, void* context);
size_t getTotalBytesUsed() const { return fTotalBytesUsed; }
size_t getTotalByteLimit() const { return fTotalByteLimit; }
* This is respected by SkBitmapProcState::possiblyScaleImage.
* 0 is no maximum at all; this is the default.
* setSingleAllocationByteLimit() returns the previous value.
size_t setSingleAllocationByteLimit(size_t maximumAllocationSize);
size_t getSingleAllocationByteLimit() const;
// returns the logical single allocation size (pinning against the budget when the cache
// is not backed by discardable memory.
size_t getEffectiveSingleAllocationByteLimit() const;
* Set the maximum number of bytes available to this cache. If the current
* cache exceeds this new value, it will be purged to try to fit within
* this new limit.
size_t setTotalByteLimit(size_t newLimit);
void purgeSharedID(uint64_t sharedID);
void purgeAll() {
DiscardableFactory discardableFactory() const { return fDiscardableFactory; }
SkCachedData* newCachedData(size_t bytes);
* Call SkDebugf() with diagnostic information about the state of the cache
void dump() const;
Rec* fHead;
Rec* fTail;
class Hash;
Hash* fHash;
DiscardableFactory fDiscardableFactory;
size_t fTotalBytesUsed;
size_t fTotalByteLimit;
size_t fSingleAllocationByteLimit;
int fCount;
SkMessageBus<PurgeSharedIDMessage, uint32_t>::Inbox fPurgeSharedIDInbox;
void checkMessages();
void purgeAsNeeded(bool forcePurge = false);
// linklist management
void moveToHead(Rec*);
void addToHead(Rec*);
void release(Rec*);
void remove(Rec*);
void init(); // called by constructors
#ifdef SK_DEBUG
void validate() const;
void validate() const {}