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/* -*- 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 */
* SurfaceCache is a service for caching temporary surfaces and decoded image
* data in imagelib.
#ifndef mozilla_image_SurfaceCache_h
#define mozilla_image_SurfaceCache_h
#include "mozilla/HashFunctions.h" // for HashGeneric and AddToHash
#include "mozilla/Maybe.h" // for Maybe
#include "mozilla/MemoryReporting.h" // for MallocSizeOf
#include "mozilla/NotNull.h"
#include "mozilla/SVGImageContext.h" // for SVGImageContext
#include "mozilla/gfx/2D.h" // for SourceSurface
#include "mozilla/gfx/Point.h" // for mozilla::gfx::IntSize
#include "gfx2DGlue.h"
#include "gfxPoint.h" // for gfxSize
#include "nsCOMPtr.h" // for already_AddRefed
#include "ImageRegion.h"
#include "PlaybackType.h"
#include "SurfaceFlags.h"
namespace mozilla {
namespace image {
class ImageResource;
class ISurfaceProvider;
class LookupResult;
class SurfaceCacheImpl;
struct SurfaceMemoryCounter;
* ImageKey contains the information we need to look up all SurfaceCache entries
* for a particular image.
using ImageKey = ImageResource*;
* SurfaceKey contains the information we need to look up a specific
* SurfaceCache entry. Together with an ImageKey, this uniquely identifies the
* surface.
* Callers should construct a SurfaceKey using the appropriate helper function
* for their image type - either RasterSurfaceKey or VectorSurfaceKey.
class SurfaceKey {
typedef gfx::IntSize IntSize;
bool operator==(const SurfaceKey& aOther) const {
return aOther.mSize == mSize && aOther.mRegion == mRegion &&
aOther.mSVGContext == mSVGContext && aOther.mPlayback == mPlayback &&
aOther.mFlags == mFlags;
PLDHashNumber Hash() const {
PLDHashNumber hash = HashGeneric(mSize.width, mSize.height);
hash = AddToHash(hash,;
hash = AddToHash(hash, HashSIC(mSVGContext));
hash = AddToHash(hash, uint8_t(mPlayback), uint32_t(mFlags));
return hash;
SurfaceKey CloneWithSize(const IntSize& aSize) const {
return SurfaceKey(aSize, mRegion, mSVGContext, mPlayback, mFlags);
const IntSize& Size() const { return mSize; }
const Maybe<ImageIntRegion>& Region() const { return mRegion; }
const SVGImageContext& SVGContext() const { return mSVGContext; }
PlaybackType Playback() const { return mPlayback; }
SurfaceFlags Flags() const { return mFlags; }
SurfaceKey(const IntSize& aSize, const Maybe<ImageIntRegion>& aRegion,
const SVGImageContext& aSVGContext, PlaybackType aPlayback,
SurfaceFlags aFlags)
: mSize(aSize),
mFlags(aFlags) {}
static PLDHashNumber HashIIR(const ImageIntRegion& aIIR) {
return aIIR.Hash();
static PLDHashNumber HashSIC(const SVGImageContext& aSIC) {
return aSIC.Hash();
friend SurfaceKey RasterSurfaceKey(const IntSize&, SurfaceFlags,
friend SurfaceKey VectorSurfaceKey(const IntSize&, const SVGImageContext&);
friend SurfaceKey VectorSurfaceKey(const IntSize&,
const Maybe<ImageIntRegion>&,
const SVGImageContext&, SurfaceFlags,
IntSize mSize;
Maybe<ImageIntRegion> mRegion;
SVGImageContext mSVGContext;
PlaybackType mPlayback;
SurfaceFlags mFlags;
inline SurfaceKey RasterSurfaceKey(const gfx::IntSize& aSize,
SurfaceFlags aFlags,
PlaybackType aPlayback) {
return SurfaceKey(aSize, Nothing(), SVGImageContext(), aPlayback, aFlags);
inline SurfaceKey VectorSurfaceKey(const gfx::IntSize& aSize,
const Maybe<ImageIntRegion>& aRegion,
const SVGImageContext& aSVGContext,
SurfaceFlags aFlags,
PlaybackType aPlayback) {
return SurfaceKey(aSize, aRegion, aSVGContext, aPlayback, aFlags);
inline SurfaceKey VectorSurfaceKey(const gfx::IntSize& aSize,
const SVGImageContext& aSVGContext) {
// We don't care about aFlags for VectorImage because none of the flags we
// have right now influence VectorImage's rendering. If we add a new flag that
// *does* affect how a VectorImage renders, we'll have to change this.
// Similarly, we don't accept a PlaybackType parameter because we don't
// currently cache frames of animated SVG images.
return SurfaceKey(aSize, Nothing(), aSVGContext, PlaybackType::eStatic,
* AvailabilityState is used to track whether an ISurfaceProvider has a surface
* available or is just a placeholder.
* To ensure that availability changes are atomic (and especially that internal
* SurfaceCache code doesn't have to deal with asynchronous availability
* changes), an ISurfaceProvider which starts as a placeholder can only reveal
* the fact that it now has a surface available via a call to
* SurfaceCache::SurfaceAvailable().
* It also tracks whether or not there are "explicit" users of this surface
* which will not accept substitutes. This is used by SurfaceCache when pruning
* unnecessary surfaces from the cache.
class AvailabilityState {
static AvailabilityState StartAvailable() { return AvailabilityState(true); }
static AvailabilityState StartAsPlaceholder() {
return AvailabilityState(false);
bool IsAvailable() const { return mIsAvailable; }
bool IsPlaceholder() const { return !mIsAvailable; }
bool CannotSubstitute() const { return mCannotSubstitute; }
void SetCannotSubstitute() { mCannotSubstitute = true; }
friend class SurfaceCacheImpl;
explicit AvailabilityState(bool aIsAvailable)
: mIsAvailable(aIsAvailable), mCannotSubstitute(false) {}
void SetAvailable() { mIsAvailable = true; }
bool mIsAvailable : 1;
bool mCannotSubstitute : 1;
enum class InsertOutcome : uint8_t {
SUCCESS, // Success (but see Insert documentation).
FAILURE, // Couldn't insert (e.g., for capacity reasons).
FAILURE_ALREADY_PRESENT // A surface with the same key is already present.
* SurfaceCache is an ImageLib-global service that allows caching of decoded
* image surfaces, temporary surfaces (e.g. for caching rotated or clipped
* versions of images), or dynamically generated surfaces (e.g. for animations).
* SurfaceCache entries normally expire from the cache automatically if they go
* too long without being accessed.
* Because SurfaceCache must support both normal surfaces and dynamically
* generated surfaces, it does not actually hold surfaces directly. Instead, it
* holds ISurfaceProvider objects which can provide access to a surface when
* requested; SurfaceCache doesn't care about the details of how this is
* accomplished.
* Sometime it's useful to temporarily prevent entries from expiring from the
* cache. This is most often because losing the data could harm the user
* experience (for example, we often don't want to allow surfaces that are
* currently visible to expire) or because it's not possible to rematerialize
* the surface. SurfaceCache supports this through the use of image locking; see
* the comments for Insert() and LockImage() for more details.
* Any image which stores surfaces in the SurfaceCache *must* ensure that it
* calls RemoveImage() before it is destroyed. See the comments for
* RemoveImage() for more details.
struct SurfaceCache {
typedef gfx::IntSize IntSize;
* Initialize static data. Called during imagelib module initialization.
static void Initialize();
* Release static data. Called during imagelib module shutdown.
static void Shutdown();
* Looks up the requested cache entry and returns a drawable reference to its
* associated surface.
* If the image associated with the cache entry is locked, then the entry will
* be locked before it is returned.
* If a matching ISurfaceProvider was found in the cache, but SurfaceCache
* couldn't obtain a surface from it (e.g. because it had stored its surface
* in a volatile buffer which was discarded by the OS) then it is
* automatically removed from the cache and an empty LookupResult is returned.
* Note that this will never happen to ISurfaceProviders associated with a
* locked image; SurfaceCache tells such ISurfaceProviders to keep a strong
* references to their data internally.
* @param aImageKey Key data identifying which image the cache entry
* belongs to.
* @param aSurfaceKey Key data which uniquely identifies the requested
* cache entry.
* @return a LookupResult which will contain a DrawableSurface
* if the cache entry was found.
static LookupResult Lookup(const ImageKey aImageKey,
const SurfaceKey& aSurfaceKey, bool aMarkUsed);
* Looks up the best matching cache entry and returns a drawable reference to
* its associated surface.
* The result may vary from the requested cache entry only in terms of size.
* @param aImageKey Key data identifying which image the cache entry
* belongs to.
* @param aSurfaceKey Key data which uniquely identifies the requested
* cache entry.
* @return a LookupResult which will contain a DrawableSurface
* if a cache entry similar to the one the caller
* requested could be found. Callers can use
* LookupResult::IsExactMatch() to check whether the
* returned surface exactly matches @aSurfaceKey.
static LookupResult LookupBestMatch(const ImageKey aImageKey,
const SurfaceKey& aSurfaceKey,
bool aMarkUsed);
* Insert an ISurfaceProvider into the cache. If an entry with the same
* ImageKey and SurfaceKey is already in the cache, Insert returns
* FAILURE_ALREADY_PRESENT. If a matching placeholder is already present, it
* is replaced.
* Cache entries will never expire as long as they remain locked, but if they
* become unlocked, they can expire either because the SurfaceCache runs out
* of capacity or because they've gone too long without being used. When it
* is first inserted, a cache entry is locked if its associated image is
* locked. When that image is later unlocked, the cache entry becomes
* unlocked too. To become locked again at that point, two things must happen:
* the image must become locked again (via LockImage()), and the cache entry
* must be touched again (via one of the Lookup() functions).
* All of this means that a very particular procedure has to be followed for
* cache entries which cannot be rematerialized. First, they must be inserted
* *after* the image is locked with LockImage(); if you use the other order,
* the cache entry might expire before LockImage() gets called or before the
* entry is touched again by Lookup(). Second, the image they are associated
* with must never be unlocked.
* If a cache entry cannot be rematerialized, it may be important to know
* whether it was inserted into the cache successfully. Insert() returns
* FAILURE if it failed to insert the cache entry, which could happen because
* of capacity reasons, or because it was already freed by the OS. If the
* cache entry isn't associated with a locked image, checking for SUCCESS or
* FAILURE is useless: the entry might expire immediately after being
* inserted, even though Insert() returned SUCCESS. Thus, many callers do not
* need to check the result of Insert() at all.
* @param aProvider The new cache entry to insert into the cache.
* @return SUCCESS if the cache entry was inserted successfully. (But see
* above for more information about when you should check this.)
* FAILURE if the cache entry could not be inserted, e.g. for capacity
* reasons. (But see above for more information about when you
* should check this.)
* FAILURE_ALREADY_PRESENT if an entry with the same ImageKey and
* SurfaceKey already exists in the cache.
static InsertOutcome Insert(NotNull<ISurfaceProvider*> aProvider);
* Mark the cache entry @aProvider as having an available surface. This turns
* a placeholder cache entry into a normal cache entry. The cache entry
* becomes locked if the associated image is locked; otherwise, it starts in
* the unlocked state.
* If the cache entry containing @aProvider has already been evicted from the
* surface cache, this function has no effect.
* It's illegal to call this function if @aProvider is not a placeholder; by
* definition, non-placeholder ISurfaceProviders should have a surface
* available already.
* @param aProvider The cache entry that now has a surface available.
static void SurfaceAvailable(NotNull<ISurfaceProvider*> aProvider);
* Checks if a surface of a given size could possibly be stored in the cache.
* If CanHold() returns false, Insert() will always fail to insert the
* surface, but the inverse is not true: Insert() may take more information
* into account than just image size when deciding whether to cache the
* surface, so Insert() may still fail even if CanHold() returns true.
* Use CanHold() to avoid the need to create a temporary surface when we know
* for sure the cache can't hold it.
* @param aSize The dimensions of a surface in pixels.
* @param aBytesPerPixel How many bytes each pixel of the surface requires.
* Defaults to 4, which is appropriate for RGBA or RGBX
* images.
* @return false if the surface cache can't hold a surface of that size.
static bool CanHold(const IntSize& aSize, uint32_t aBytesPerPixel = 4);
static bool CanHold(size_t aSize);
* Locks an image. Any of the image's cache entries which are either inserted
* or accessed while the image is locked will not expire.
* Locking an image does not automatically lock that image's existing cache
* entries. A call to LockImage() guarantees that entries which are inserted
* afterward will not expire before the next call to UnlockImage() or
* UnlockSurfaces() for that image. Cache entries that are accessed via
* Lookup() or LookupBestMatch() after a LockImage() call will also not expire
* until the next UnlockImage() or UnlockSurfaces() call for that image. Any
* other cache entries owned by the image may expire at any time.
* All of an image's cache entries are removed by RemoveImage(), whether the
* image is locked or not.
* It's safe to call LockImage() on an image that's already locked; this has
* no effect.
* You must always unlock any image you lock. You may do this explicitly by
* calling UnlockImage(), or implicitly by calling RemoveImage(). Since you're
* required to call RemoveImage() when you destroy an image, this doesn't
* impose any additional requirements, but it's preferable to call
* UnlockImage() earlier if it's possible.
* @param aImageKey The image to lock.
static void LockImage(const ImageKey aImageKey);
* Unlocks an image, allowing any of its cache entries to expire at any time.
* It's OK to call UnlockImage() on an image that's already unlocked; this has
* no effect.
* @param aImageKey The image to unlock.
static void UnlockImage(const ImageKey aImageKey);
* Unlocks the existing cache entries of an image, allowing them to expire at
* any time.
* This does not unlock the image itself, so accessing the cache entries via
* Lookup() or LookupBestMatch() will lock them again, and prevent them from
* expiring.
* This is intended to be used in situations where it's no longer clear that
* all of the cache entries owned by an image are needed. Calling
* UnlockSurfaces() and then taking some action that will cause Lookup() to
* touch any cache entries that are still useful will permit the remaining
* entries to expire from the cache.
* If the image is unlocked, this has no effect.
* @param aImageKey The image which should have its existing cache entries
* unlocked.
static void UnlockEntries(const ImageKey aImageKey);
* Removes all cache entries (including placeholders) associated with the
* given image from the cache. If the image is locked, it is automatically
* unlocked.
* This MUST be called, at a minimum, when an Image which could be storing
* entries in the surface cache is destroyed. If another image were allocated
* at the same address it could result in subtle, difficult-to-reproduce bugs.
* @param aImageKey The image which should be removed from the cache.
static void RemoveImage(const ImageKey aImageKey);
* Attempts to remove cache entries (including placeholders) associated with
* the given image from the cache, assuming there is an equivalent entry that
* it is able substitute that entry with. Note that this only applies if the
* image is in factor of 2 mode. If it is not, this operation does nothing.
* @param aImageKey The image whose cache which should be pruned.
static void PruneImage(const ImageKey aImageKey);
* Removes all rasterized cache entries (including placeholders) associated
* with the given image from the cache. Any blob recordings are marked as
* dirty and must be regenerated.
* @param aImageKey The image whose cache which should be regenerated.
* @returns true if any recordings were invalidated, else false.
static bool InvalidateImage(const ImageKey aImageKey);
* Evicts all evictable entries from the cache.
* All entries are evictable except for entries associated with locked images.
* Non-evictable entries can only be removed by RemoveImage().
static void DiscardAll();
* Calls Reset on the ISurfaceProvider (which is currently only implemented
* for AnimationSurfaceProvider). This is needed because we need to call Reset
* on AnimationSurfaceProvider while they are in placeholder status and there
* is no way to access a surface cache entry from outside of the surface cache
* when it's in placeholder status.
static void ResetAnimation(const ImageKey aImageKey,
const SurfaceKey& aSurfaceKey);
* Collects an accounting of the surfaces contained in the SurfaceCache for
* the given image, along with their size and various other metadata.
* This is intended for use with memory reporting.
* @param aImageKey The image to report memory usage for.
* @param aCounters An array into which the report for each surface will
* be written.
* @param aMallocSizeOf A fallback malloc memory reporting function.
static void CollectSizeOfSurfaces(const ImageKey aImageKey,
nsTArray<SurfaceMemoryCounter>& aCounters,
MallocSizeOf aMallocSizeOf);
* @return maximum capacity of the SurfaceCache in bytes. This is only exposed
* for use by tests; normal code should use CanHold() instead.
static size_t MaximumCapacity();
* @return true if the given size is valid.
static bool IsLegalSize(const IntSize& aSize);
* @return clamped size for the given vector image size to rasterize at.
static IntSize ClampVectorSize(const IntSize& aSize);
* @return clamped size for the given image and size to rasterize at.
static IntSize ClampSize(const ImageKey aImageKey, const IntSize& aSize);
* Release image on main thread.
* The function uses SurfaceCache to release pending releasing images quickly.
static void ReleaseImageOnMainThread(already_AddRefed<image::Image> aImage,
bool aAlwaysProxy = false);
* Clear all pending releasing images.
static void ClearReleasingImages();
virtual ~SurfaceCache() = 0; // Forbid instantiation.
} // namespace image
} // namespace mozilla
#endif // mozilla_image_SurfaceCache_h