support scaledimagecache instantiable using discardablememory

src/core/SkScaledImageCache.h

 /*
  * 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 SkScaledImageCache_DEFINED
 #define SkScaledImageCache_DEFINED
 
 #include "SkBitmap.h"
 
+class SkDiscardableMemory;
 class SkMipMap;
 
 /**
  *  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 SkScaledImageCache {
 public:
     struct ID;
 
+    /**
+     *  Returns a locked/pinned SkDiscardableMemory instance for the specified
+     *  number of bytes, or NULL on failure.
+     */
+    typedef SkDiscardableMemory* (*DiscardableFactory)(size_t bytes);
+
     /*
      *  The following static methods are thread-safe wrappers around a global
      *  instance of this cache.
      */
 
     static ID* FindAndLock(uint32_t pixelGenerationID,
                            int32_t width,
                            int32_t height,
                            SkBitmap* returnedBitmap);
 
@@ skipping 11 matching lines @@
     static ID* AddAndLock(const SkBitmap& original, SkScalar scaleX,
                           SkScalar scaleY, const SkBitmap& bitmap);
     static ID* AddAndLockMip(const SkBitmap& original, const SkMipMap* mipMap);
 
     static void Unlock(ID*);
 
     static size_t GetBytesUsed();
     static size_t GetByteLimit();
     static size_t SetByteLimit(size_t newLimit);
 
+    static SkBitmap::Allocator* GetAllocator();
+
     ///////////////////////////////////////////////////////////////////////////
 
+    /**
+     *  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 getBytesUsed() and
+     *  getByteLimit() will return 0, and setByteLimit will ignore its argument
+     *  and return 0.
+     */
+    SkScaledImageCache(DiscardableFactory);
+
+    /**
+     *  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 setByteLimit.
+     */
     SkScaledImageCache(size_t byteLimit);
+
     ~SkScaledImageCache();
 
     /**
      *  Search the cache for a matching bitmap (using generationID,
      *  width, and height as a search key). If found, return it in
      *  returnedBitmap, and return its ID pointer. Use the returned
      *  ptr to unlock the cache when you are done using
      *  returnedBitmap.
      *
      *  If a match is not found, returnedBitmap will be unmodifed, and
@@ skipping 44 matching lines @@
     size_t getBytesUsed() const { return fBytesUsed; }
     size_t getByteLimit() const { return fByteLimit; }
 
     /**
      *  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 setByteLimit(size_t newLimit);
 
+    SkBitmap::Allocator* allocator() const { return fAllocator; };
+
 public:
     struct Rec;
     struct Key;
 private:
     Rec*    fHead;
     Rec*    fTail;
 
     class Hash;
     Hash*   fHash;
 
+    DiscardableFactory  fDiscardableFactory;
+    // the allocator is NULL or one that matches discardables
+    SkBitmap::Allocator* fAllocator;
+
     size_t  fBytesUsed;
     size_t  fByteLimit;
     int     fCount;
 
     Rec* findAndLock(uint32_t generationID, SkScalar sx, SkScalar sy,
                      const SkIRect& bounds);
     Rec* findAndLock(const Key& key);
     ID* addAndLock(Rec* rec);
 
     void purgeAsNeeded();
 
     // linklist management
     void moveToHead(Rec*);
     void addToHead(Rec*);
     void detach(Rec*);
+
+    void init();    // called by constructors
+
 #ifdef SK_DEBUG
     void validate() const;
 #else
     void validate() const {}
 #endif
 };
 #endif