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 110 matching lines @@
                   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);
+        -m_externallyAllocatedMemory + 1);
   }
 }
 
 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_externallyAllocatedMemory == 1)

[jbroman, 2017/03/07 18:00:04]

Use of this magic value is confusing. I'd suggest just adding a boolean member
rather being clever.

[sof, 2017/03/07 19:14:03]

It's not particularly clever; I can switch to an int64_t though (and avoid
spending a word to encode one bit of info on 64-bit arches.)

[jbroman, 2017/03/07 19:29:05]

(u)int64_t + boolean in a bitfield would do the trick, though to be honest I'd
be surprised if we had enough SerializedScriptValues floating around for the
single word to contribute significantly to memory consumption.

As-is, I'm having to track what 1 means, and why 1 is added to size sometimes,
and so on. It's not immediately apparent to me. (Since dataLengthInBytes isn't
going to change, I believe all we _really_ need to store is two bits: "is my
buffer accounted for", and "are my transferables accounted for".)

[sof, 2017/03/07 19:30:20]

Done.

+    return;
+  if (m_externallyAllocatedMemory) {
+    v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(
+        -(m_externallyAllocatedMemory - 1));
+    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) {
+      int64_t bufferSize =
+          static_cast<int64_t>(m_arrayBufferContentsArray->at(i).sizeInBytes());
+      v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(
+          -bufferSize);
+    }
+    // Mark the value as needing re-registration by its target context.
+    m_externallyAllocatedMemory = static_cast<intptr_t>(1);
+  }
+}
+
 void SerializedScriptValue::registerMemoryAllocatedWithCurrentScriptContext() {
-  if (m_externallyAllocatedMemory)
+  if (m_externallyAllocatedMemory != 1)
     return;
 
-  m_externallyAllocatedMemory = static_cast<intptr_t>(dataLengthInBytes());
+  bool registerTransferables =
+      m_externallyAllocatedMemory == static_cast<intptr_t>(1);
+  size_t size = dataLengthInBytes();
   v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(
-      m_externallyAllocatedMemory);
+      static_cast<intptr_t>(size));
+  m_externallyAllocatedMemory = static_cast<int64_t>(size ? (size + 1) : 0);
+  if (registerTransferables) {
+    DCHECK(m_arrayBufferContentsArray);
+    for (size_t i = 0; i < m_arrayBufferContentsArray->size(); ++i) {
+      v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(
+          m_arrayBufferContentsArray->at(i).sizeInBytes());
+    }
+  }
 }
 
 }  // namespace blink