Add a ref-counted data holder to ArrayBufferContents

Source/wtf/ArrayBufferContents.h

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 11 matching lines @@
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef ArrayBufferContents_h
 #define ArrayBufferContents_h
 
 #include "wtf/Assertions.h"
 #include "wtf/Noncopyable.h"
+#include "wtf/RefPtr.h"
+#include "wtf/ThreadSafeRefCounted.h"
 #include "wtf/WTF.h"
 #include "wtf/WTFExport.h"
 
 namespace WTF {
 
 class WTF_EXPORT ArrayBufferContents {
     WTF_MAKE_NONCOPYABLE(ArrayBufferContents);
 public:
     enum InitializationPolicy {
         ZeroInitialize,
         DontInitialize
     };
 
+    enum SharingType {
+        NotShared,
+        Shared,
+    };
+
     ArrayBufferContents();
-    ArrayBufferContents(unsigned numElements, unsigned elementByteSize, ArrayBufferContents::InitializationPolicy);
+    ArrayBufferContents(unsigned numElements, unsigned elementByteSize, SharingType isShared, ArrayBufferContents::InitializationPolicy);
 
     // Use with care. data must be allocated with allocateMemory.
     // ArrayBufferContents will take ownership of the data and free it (using freeMemory)
     // upon destruction.
     // This constructor will not call observer->StartObserving(), so it is a responsibility
     // of the caller to make sure JS knows about external memory.
-    ArrayBufferContents(void* data, unsigned sizeInBytes);
+    ArrayBufferContents(void* data, unsigned sizeInBytes, SharingType isShared);
 
     ~ArrayBufferContents();
 
-    void clear();
+    void neuter();
 
-    void* data() const { return m_data; }
-    unsigned sizeInBytes() const { return m_sizeInBytes; }
+    void* data() const { return m_holder ? m_holder->data() : nullptr; }
+    unsigned sizeInBytes() const { return m_holder ? m_holder->sizeInBytes() : 0; }
+    bool isShared() const { return m_holder ? m_holder->isShared() : false; }
 
     void transfer(ArrayBufferContents& other);
+    void shareWith(ArrayBufferContents& other);
     void copyTo(ArrayBufferContents& other);
 
     static void allocateMemory(size_t, InitializationPolicy, void*&);
     static void freeMemory(void*, size_t);
     static void setAdjustAmoutOfExternalAllocatedMemoryFunction(AdjustAmountOfExternalAllocatedMemoryFunction function)
     {
         ASSERT(!s_adjustAmountOfExternalAllocatedMemoryFunction);
         s_adjustAmountOfExternalAllocatedMemoryFunction = function;
     }
 
 private:
-    void* m_data;
-    unsigned m_sizeInBytes;
+    class DataHolder : public ThreadSafeRefCounted<DataHolder> {
+        WTF_MAKE_NONCOPYABLE(DataHolder);
+    public:
+        DataHolder();
+        ~DataHolder();
+
+        void allocateNew(unsigned sizeInBytes, SharingType isShared, InitializationPolicy);
+        void adopt(void* data, unsigned sizeInBytes, SharingType isShared);
+        void copyMemoryTo(DataHolder& other);
+
+        void* data() const { return m_data; }
+        unsigned sizeInBytes() const { return m_sizeInBytes; }
+        bool isShared() const { return m_isShared == Shared; }
+
+    private:
+        void* m_data;
+        unsigned m_sizeInBytes;
+        SharingType m_isShared;
+    };
+
+    RefPtr<DataHolder> m_holder;
     static AdjustAmountOfExternalAllocatedMemoryFunction s_adjustAmountOfExternalAllocatedMemoryFunction;
 };
 
 } // namespace WTF
 
 #endif // ArrayBufferContents_h