postMessage(): transfer allocation costs along with value.

third_party/WebKit/Source/bindings/core/v8/SerializedScriptValue.cpp

 /*
  * Copyright (C) 2010 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 91 matching lines @@
   StringBuffer<UChar> buffer(stringLength);
   const UChar* src = reinterpret_cast<const UChar*>(data);
   UChar* dst = buffer.characters();
   for (size_t i = 0; i < stringLength; i++)
     dst[i] = ntohs(src[i]);
 
   return adoptRef(new SerializedScriptValue(String::adopt(buffer)));
 }
 
 SerializedScriptValue::SerializedScriptValue()
-    : m_externallyAllocatedMemory(0) {}
+    : m_externallyAllocatedMemory(0),
+      m_adjustTransferableExternalAllocationOnContextTransfer(false) {}
 
 SerializedScriptValue::SerializedScriptValue(const String& wireData)
-    : m_externallyAllocatedMemory(0) {
+    : m_externallyAllocatedMemory(0),
+      m_adjustTransferableExternalAllocationOnContextTransfer(false) {
   size_t byteLength = wireData.length() * 2;
   m_dataBuffer.reset(static_cast<uint8_t*>(WTF::Partitions::bufferMalloc(
       byteLength, "SerializedScriptValue buffer")));
   m_dataBufferSize = byteLength;
   wireData.copyTo(reinterpret_cast<UChar*>(m_dataBuffer.get()), 0,
                   wireData.length());
 }
 
 SerializedScriptValue::~SerializedScriptValue() {
   // If the allocated memory was not registered before, then this class is
   // likely used in a context other than Worker's onmessage environment and the
   // presence of current v8 context is not guaranteed. Avoid calling v8 then.
   if (m_externallyAllocatedMemory) {
     ASSERT(v8::Isolate::GetCurrent());
     v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(
-        -m_externallyAllocatedMemory);
+        -static_cast<int64_t>(m_externallyAllocatedMemory));
   }
 }
 
 PassRefPtr<SerializedScriptValue> SerializedScriptValue::nullValue() {
   // UChar rather than uint8_t here to get host endian behavior.
   static const UChar kNullData[] = {0xff09, 0x3000};
   return create(reinterpret_cast<const char*>(kNullData), sizeof(kNullData));
 }
 
 String SerializedScriptValue::toWireString() const {
@@ skipping 295 matching lines @@
 
       if (isNeuterable) {
         for (const auto& bufferHandle : bufferHandles)
           bufferHandle->Neuter();
       }
     }
   }
   return contents;
 }
 
+void SerializedScriptValue::unregisterMemoryAllocatedByCurrentScriptContext() {
+  if (m_adjustTransferableExternalAllocationOnContextTransfer)
+    return;
+  if (m_externallyAllocatedMemory) {
+    v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(
+        -static_cast<int64_t>(m_externallyAllocatedMemory));
+    m_externallyAllocatedMemory = 0;
+  }
+  // TODO: if other transferables start accounting for their external
+  // allocations with V8, extend this with corresponding cases.
+  if (m_arrayBufferContentsArray) {
+    for (size_t i = 0; i < m_arrayBufferContentsArray->size(); ++i) {

[jbroman, 2017/03/08 22:43:16]

super-nit: here and below, a range-based loop would be more concise:

for (const auto& buffer : *m_arrayBufferContentsArray) {
}

[sof, 2017/03/09 06:24:33]

Switched idiom.

+      WTF::ArrayBufferContents& buffer = m_arrayBufferContentsArray->at(i);
+      buffer.adjustExternalAllocatedMemoryUponContextTransfer(
+          WTF::ArrayBufferContents::Leave);
+    }
+    // Mark value as needing re-registration of external allocation
+    // costs in its target context, as handled by
+    // |registerMemoryAllocatedWithCurrentScriptContext()|.
+    m_adjustTransferableExternalAllocationOnContextTransfer = true;
+  }
+}
+
 void SerializedScriptValue::registerMemoryAllocatedWithCurrentScriptContext() {
   if (m_externallyAllocatedMemory)
     return;
 
-  m_externallyAllocatedMemory = static_cast<intptr_t>(dataLengthInBytes());
-  v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(
-      m_externallyAllocatedMemory);
+  m_externallyAllocatedMemory = dataLengthInBytes();
+  int64_t diff = static_cast<int64_t>(m_externallyAllocatedMemory);

[jbroman, 2017/03/08 22:43:16]

nit: intptr_t, since that's what AdjustAmountOfExternalAllocatedMemory takes and
nothing else is done with this?

[sof, 2017/03/09 06:24:33]

int64_t Isolate::AdjustAmountOfExternalAllocatedMemory(int64_t) is the signature
we're working with.

+  DCHECK_GE(diff, 0);
+  v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(diff);
+  if (m_adjustTransferableExternalAllocationOnContextTransfer) {
+    DCHECK(m_arrayBufferContentsArray);
+    for (size_t i = 0; i < m_arrayBufferContentsArray->size(); ++i) {
+      WTF::ArrayBufferContents& buffer = m_arrayBufferContentsArray->at(i);
+      buffer.adjustExternalAllocatedMemoryUponContextTransfer(
+          WTF::ArrayBufferContents::Enter);
+    }
+    m_adjustTransferableExternalAllocationOnContextTransfer = false;
+  }
 }
 
 }  // namespace blink