Sharing of SharedArrayBuffer via PostMessage transfer

Source/wtf/ArrayBufferContents.cpp

 /*
  * 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 17 matching lines @@
 #include "wtf/ArrayBufferContents.h"
 
 #include "wtf/Assertions.h"
 #include "wtf/PartitionAlloc.h"
 #include "wtf/Partitions.h"
 #include <string.h>
 
 namespace WTF {
 
 ArrayBufferContents::ArrayBufferContents()
-    : m_data(0)
-    , m_sizeInBytes(0)
-    , m_deallocationObserver(0) { }
+    : m_holder(adoptRef(new DataHolder())) { }
 
-ArrayBufferContents::ArrayBufferContents(unsigned numElements, unsigned elementByteSize, ArrayBufferContents::InitializationPolicy policy)
-    : m_data(0)
-    , m_sizeInBytes(0)
-    , m_deallocationObserver(0)
+ArrayBufferContents::ArrayBufferContents(unsigned numElements, unsigned elementByteSize, SharingType isShared, ArrayBufferContents::InitializationPolicy policy)
+    : m_holder(adoptRef(new DataHolder()))
 {
     // Do not allow 32-bit overflow of the total size.
+    unsigned totalSize = numElements * elementByteSize;
     if (numElements) {
-        unsigned totalSize = numElements * elementByteSize;
         if (totalSize / numElements != elementByteSize) {
-            m_data = 0;
             return;
         }
     }
-    allocateMemory(numElements * elementByteSize, policy, m_data);
-    m_sizeInBytes = numElements * elementByteSize;
+
+    m_holder->allocateNew(totalSize, isShared, policy, nullptr);
 }
 
 ArrayBufferContents::ArrayBufferContents(
-    void* data, unsigned sizeInBytes, ArrayBufferDeallocationObserver* observer)
-    : m_data(data)
-    , m_sizeInBytes(sizeInBytes)
-    , m_deallocationObserver(observer)
+    void* data, unsigned sizeInBytes, SharingType isShared, ArrayBufferDeallocationObserver* observer)
+    : m_holder(adoptRef(new DataHolder()))
 {
-    if (!m_data) {
-        ASSERT(!m_sizeInBytes);
-        m_sizeInBytes = 0;
-        // Allow null data if size is 0 bytes, make sure m_data is valid pointer.
+    if (!data) {
+        ASSERT(!sizeInBytes);
+        sizeInBytes = 0;
+        // Allow null data if size is 0 bytes, make sure data is valid pointer.
         // (partitionAllocGeneric guarantees valid pointer for size 0)
-        allocateMemory(0, ZeroInitialize, m_data);
+        m_holder->allocateNew(sizeInBytes, isShared, ZeroInitialize, observer);
+    } else {
+        m_holder->adopt(data, sizeInBytes, isShared, observer);
     }
 }
 
 ArrayBufferContents::~ArrayBufferContents()
 {
-    freeMemory(m_data, m_sizeInBytes);
     clear();
 }
 
 void ArrayBufferContents::clear()
 {
-    if (m_data && m_deallocationObserver)
-        m_deallocationObserver->arrayBufferDeallocated(m_sizeInBytes);
-    m_data = 0;
-    m_sizeInBytes = 0;
-    m_deallocationObserver = 0;
+    m_holder.clear();
 }
 
 void ArrayBufferContents::transfer(ArrayBufferContents& other)
 {
-    ASSERT(!other.m_data);
-    other.m_data = m_data;
-    other.m_sizeInBytes = m_sizeInBytes;
-    clear();
+    ASSERT(!other.m_holder->data());
+    other.m_holder = m_holder;
+    if (!m_holder->isShared())
+        clear();
 }
 
 void ArrayBufferContents::copyTo(ArrayBufferContents& other)
 {
-    ASSERT(!other.m_sizeInBytes);
-    other.freeMemory(other.m_data, other.m_sizeInBytes);
-    allocateMemory(m_sizeInBytes, DontInitialize, other.m_data);
-    if (!other.m_data)
-        return;
-    memcpy(other.m_data, m_data, m_sizeInBytes);
-    other.m_sizeInBytes = m_sizeInBytes;
+    // TODO(binji): where is this function used? It probably shouldn't be used
+    // for shared array buffers.
+    ASSERT(!m_holder->isShared() && !other.m_holder->isShared());
+
+    ASSERT(!other.m_holder->sizeInBytes());
+
+    other.m_holder = adoptRef(new DataHolder());
+    m_holder->copyTo(*other.m_holder);
 }
 
 void ArrayBufferContents::allocateMemory(size_t size, InitializationPolicy policy, void*& data)
 {
     data = partitionAllocGenericFlags(WTF::Partitions::getBufferPartition(), PartitionAllocReturnNull, size);
     if (policy == ZeroInitialize && data)
         memset(data, '\0', size);
 }
 
 void ArrayBufferContents::freeMemory(void* data, size_t)
 {
     partitionFreeGeneric(WTF::Partitions::getBufferPartition(), data);
 }
 
+ArrayBufferContents::DataHolder::DataHolder()
+    : m_data(nullptr)
+    , m_sizeInBytes(0)
+    , m_isShared(NotShared)
+    , m_deallocationObserver(nullptr) { }
+
+ArrayBufferContents::DataHolder::~DataHolder()
+{
+    ArrayBufferContents::freeMemory(m_data, m_sizeInBytes);
+
+    if (m_data && m_deallocationObserver)
+        m_deallocationObserver->arrayBufferDeallocated(m_sizeInBytes);
+
+    m_data = nullptr;
+    m_sizeInBytes = 0;
+    m_isShared = NotShared;
+    m_deallocationObserver = nullptr;
+}
+
+void ArrayBufferContents::DataHolder::allocateNew(unsigned sizeInBytes, SharingType isShared, InitializationPolicy policy, ArrayBufferDeallocationObserver* observer)
+{
+    ASSERT(!m_data);
+    void* data = nullptr;
+    allocateMemory(sizeInBytes, policy, data);
+    m_data = data;
+    m_sizeInBytes = sizeInBytes;
+    m_isShared = isShared;
+    m_deallocationObserver = observer;
+}
+
+void ArrayBufferContents::DataHolder::adopt(void* data, unsigned sizeInBytes, SharingType isShared, ArrayBufferDeallocationObserver* observer)
+{
+    ASSERT(!m_data);
+    m_data = data;
+    m_sizeInBytes = sizeInBytes;
+    m_isShared = isShared;
+    m_deallocationObserver = observer;
+}
+
+void ArrayBufferContents::DataHolder::copyTo(DataHolder& other)
+{
+    other.allocateNew(m_sizeInBytes, m_isShared, DontInitialize, m_deallocationObserver);

[Yuki, 2015/06/10 07:44:55]

I'm concerned about the (implicit) change of the API spec.

The old implementation does:
    other.freeMemory(other.m_data, other.m_sizeInBytes);
before allocating a new memory where the data will be copied.
However, your new implementation actually does:
    ASSERT(!other.m_data);
    allocateMemory(sizeInBytes, policy, other.m_data);

Since ArrayBufferContents's ctor allocates memory even if the size is zero in
order to give it a unique address, I'm afraid that it's not always true that
other.m_data == nullptr.  It's safer to call freeMemory, isn't it?  Or, are you
sure it's always true that other.m_data == nullptr?

[binji, 2015/06/10 20:53:40]

Yes, you're right. Done.

+    memcpy(other.data(), data(), sizeInBytes());
+}
+
+void ArrayBufferContents::DataHolder::setDeallocationObserver(ArrayBufferDeallocationObserver& observer)
+{
+    if (!m_deallocationObserver) {
+        m_deallocationObserver = &observer;
+        m_deallocationObserver->blinkAllocatedMemory(m_sizeInBytes);
+    }
+}
+
+void ArrayBufferContents::DataHolder::setDeallocationObserverWithoutAllocationNotification(ArrayBufferDeallocationObserver& observer)
+{
+    if (!m_deallocationObserver) {
+        m_deallocationObserver = &observer;
+    }
+}
+
 } // namespace WTF