Sharing of SharedArrayBuffer via PostMessage transfer

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/ArrayBufferDeallocationObserver.h"
 #include "wtf/Noncopyable.h"
+#include "wtf/RefPtr.h"
+#include "wtf/ThreadSafeRefCounted.h"
 #include "wtf/WTFExport.h"
 
 namespace WTF {
 
 class WTF_EXPORT ArrayBufferContents {
     WTF_MAKE_NONCOPYABLE(ArrayBufferContents);
 public:
     enum InitializationPolicy {
         ZeroInitialize,
         DontInitialize
     };
 
     ArrayBufferContents();
-    ArrayBufferContents(unsigned numElements, unsigned elementByteSize, ArrayBufferContents::InitializationPolicy);
+    ArrayBufferContents(unsigned numElements, unsigned elementByteSize, bool isShared, ArrayBufferContents::InitializationPolicy);

[Yuki, 2015/06/09 06:18:08]

Our policy (style guide) prefers enum value to boolean value.
For example,
  enum Sharable {NON_SHARED_BUFFER, SHARED_BUFFER};
  ArrayBufferContents(..., Sharable isShared, ...);

Just as an example.  I expect better names ;)

[binji, 2015/06/10 06:04:39]

Done.

 
     // 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, ArrayBufferDeallocationObserver*);
+    ArrayBufferContents(void* data, unsigned sizeInBytes, bool isShared, ArrayBufferDeallocationObserver*);
 
     ~ArrayBufferContents();
 
     void clear();
 
-    void* data() const { return m_data; }
-    unsigned sizeInBytes() const { return m_sizeInBytes; }
+    void* data() const { return m_holder ? m_holder->m_data : nullptr; }
+    unsigned sizeInBytes() const { return m_holder ? m_holder->m_sizeInBytes : 0; }
+    bool isShared() const { return m_holder ? m_holder->m_isShared : false; }
 
     void setDeallocationObserver(ArrayBufferDeallocationObserver& observer)
     {
-        if (!m_deallocationObserver) {
-            m_deallocationObserver = &observer;
-            m_deallocationObserver->blinkAllocatedMemory(m_sizeInBytes);
+        ASSERT(m_holder);
+        if (!m_holder->m_deallocationObserver) {
+            m_holder->m_deallocationObserver = &observer;
+            m_holder->m_deallocationObserver->blinkAllocatedMemory(m_holder->m_sizeInBytes);
         }
     }
     void setDeallocationObserverWithoutAllocationNotification(ArrayBufferDeallocationObserver& observer)
     {
-        if (!m_deallocationObserver) {
-            m_deallocationObserver = &observer;
+        ASSERT(m_holder);
+        if (!m_holder->m_deallocationObserver) {
+            m_holder->m_deallocationObserver = &observer;
         }
     }
 
     void transfer(ArrayBufferContents& other);
     void copyTo(ArrayBufferContents& other);
 
     static void allocateMemory(size_t, InitializationPolicy, void*&);
     static void freeMemory(void*, size_t);
 
 private:
-    void* m_data;
-    unsigned m_sizeInBytes;
-    ArrayBufferDeallocationObserver* m_deallocationObserver;
+    class DataHolder : public ThreadSafeRefCounted<DataHolder> {
+        WTF_MAKE_NONCOPYABLE(DataHolder);
+    public:
+        DataHolder();
+        ~DataHolder();
+
+        void adopt(void* data, unsigned sizeInBytes, bool shared, ArrayBufferDeallocationObserver*);
+        void copyToWithoutBuffer(DataHolder& other);
+
+        void* m_data;

[Yuki, 2015/06/09 06:18:08]

Maybe you think it's overkilling, but I'd recommend to have regular accessors.

public:
  void* data() const { return m_data; }
private:
  void* m_data;

Then, it's crystal clear that only adopt() changes the contents.

[binji, 2015/06/10 06:04:39]

Done.

+        unsigned m_sizeInBytes;
+        bool m_isShared;
+        ArrayBufferDeallocationObserver* m_deallocationObserver;
+    };
+
+    RefPtr<DataHolder> m_holder;
 };
 
 } // namespace WTF
 
 #endif // ArrayBufferContents_h