The Tor Browser: image/src/SurfaceCache.h@ac0c01689b40 (annotated)

image/src/SurfaceCache.h@ac0c01689b40 (annotated)

image/src/SurfaceCache.h

Thu, 15 Jan 2015 15:59:08 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 15 Jan 2015 15:59:08 +0100
branch: TOR_BUG_9701
changeset 10: ac0c01689b40
permissions: -rw-r--r--

Implement a real Private Browsing Mode condition by changing the API/ABI;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- 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/. */
 /**
  * SurfaceCache is a service for caching temporary surfaces in imagelib.
  */
 #ifndef MOZILLA_IMAGELIB_SURFACECACHE_H_
 #define MOZILLA_IMAGELIB_SURFACECACHE_H_
 #include "mozilla/HashFunctions.h"  // for HashGeneric and AddToHash
 #include "gfxPoint.h"               // for gfxSize
 #include "nsCOMPtr.h"               // for already_AddRefed
 #include "mozilla/gfx/Point.h"      // for mozilla::gfx::IntSize
 #include "SVGImageContext.h"        // for SVGImageContext
 class gfxDrawable;
 namespace mozilla {
 namespace gfx {
 class DrawTarget;
 } // namespace gfx
 namespace image {
 class Image;
 /*
  * ImageKey contains the information we need to look up all cached surfaces for
  * a particular image.
  */
 typedef Image* ImageKey;
 /*
  * SurfaceKey contains the information we need to look up a specific cached
  * surface. Together with an ImageKey, this uniquely identifies the surface.
  *
  * XXX(seth): Right now this is specialized to the needs of VectorImage. We'll
  * generalize it in bug 919071.
  */
 class SurfaceKey
 {
   typedef gfx::IntSize IntSize;
 public:
   SurfaceKey(const IntSize& aSize,
              const gfxSize aScale,
              const SVGImageContext* aSVGContext,
              const float aAnimationTime,
              const uint32_t aFlags)
     : mSize(aSize)
     , mScale(aScale)
     , mSVGContextIsValid(aSVGContext != nullptr)
     , mAnimationTime(aAnimationTime)
     , mFlags(aFlags)
   {
     // XXX(seth): Would love to use Maybe<T> here, but see bug 913586.
     if (mSVGContextIsValid)
       mSVGContext = *aSVGContext;
   }
   bool operator==(const SurfaceKey& aOther) const
   {
     bool matchesSVGContext = aOther.mSVGContextIsValid == mSVGContextIsValid &&
                              (!mSVGContextIsValid || aOther.mSVGContext == mSVGContext);
     return aOther.mSize == mSize &&
            aOther.mScale == mScale &&
            matchesSVGContext &&
            aOther.mAnimationTime == mAnimationTime &&
            aOther.mFlags == mFlags;
   }
   uint32_t Hash() const
   {
     uint32_t hash = HashGeneric(mSize.width, mSize.height);
     hash = AddToHash(hash, mScale.width, mScale.height);
     hash = AddToHash(hash, mSVGContextIsValid, mSVGContext.Hash());
     hash = AddToHash(hash, mAnimationTime, mFlags);
     return hash;
   }
   IntSize Size() const { return mSize; }
 private:
   IntSize         mSize;
   gfxSize         mScale;
   SVGImageContext mSVGContext;
   bool            mSVGContextIsValid;
   float           mAnimationTime;
   uint32_t        mFlags;
 };
 /**
  * SurfaceCache is an imagelib-global service that allows caching of temporary
  * surfaces. Surfaces expire from the cache automatically if they go too long
  * without being accessed.
  *
  * SurfaceCache is not thread-safe; it should only be accessed from the main
  * thread.
  */
 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();
   /*
    * Look up a surface in the cache.
    *
    * @param aImageKey    Key data identifying which image the surface belongs to.
    * @param aSurfaceKey  Key data which uniquely identifies the requested surface.
    *
    * @return the requested surface, or nullptr if not found.
    */
   static already_AddRefed<gfxDrawable> Lookup(const ImageKey    aImageKey,
                                               const SurfaceKey& aSurfaceKey);
   /*
    * Insert a surface into the cache. It is an error to call this function
    * without first calling Lookup to verify that the surface is not already in
    * the cache.
    *
    * @param aTarget      The new surface (in the form of a DrawTarget) to insert
    *                     into the cache.
    * @param aImageKey    Key data identifying which image the surface belongs to.
    * @param aSurfaceKey  Key data which uniquely identifies the requested surface.
    */
   static void Insert(mozilla::gfx::DrawTarget* aTarget,
                      const ImageKey            aImageKey,
                      const SurfaceKey&         aSurfaceKey);
   /*
    * 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.
    *
    * @return false if the surface cache can't hold a surface of that size.
    */
   static bool CanHold(const IntSize& aSize);
   /*
    * Evicts any cached surfaces associated with the given image from the cache.
    * This MUST be called, at a minimum, when the image 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 Discard(const ImageKey aImageKey);
   /*
    * Evicts all caches surfaces from ths cache.
    */
   static void DiscardAll();
 private:
   virtual ~SurfaceCache() = 0;  // Forbid instantiation.
 };
 } // namespace image
 } // namespace mozilla
 #endif // MOZILLA_IMAGELIB_SURFACECACHE_H_

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image/src/SurfaceCache.h@ac0c01689b40 (annotated)

image/src/SurfaceCache.h