[wrapper-tracing] Don't call into V8 during heap snapshot creation

third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp

 /*
  * Copyright (C) 2009 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 117 matching lines @@
   v8::Isolate* m_isolate;
 };
 
 class HeapSnaphotWrapperVisitor : public ScriptWrappableVisitor,
                                   public v8::PersistentHandleVisitor {
  public:
   explicit HeapSnaphotWrapperVisitor(v8::Isolate* isolate)
       : ScriptWrappableVisitor(isolate),
         m_currentParent(nullptr),
         m_onlyTraceSingleLevel(false),
         m_firstScriptWrappableTraced(false) {}

[haraken, 2017/02/03 07:46:12]

Shall we add DCHECK(isMainThread()) (for a documentation purpose)?

[Michael Lippautz, 2017/02/03 15:51:31]

Good idea, done.

 
   // Collect interesting V8 roots for the heap snapshot. Currently these are
   // DOM nodes.
   void collectV8Roots() { m_isolate->VisitHandlesWithClassIds(this); }
 
   void VisitPersistentHandle(v8::Persistent<v8::Value>* value,
                              uint16_t classId) override {
     if (classId != WrapperTypeInfo::NodeClassId)
       return;
 
@@ skipping 39 matching lines @@
         groupChildren.insert(persistentForWrappable(node));
       }
       m_groups.push_back(std::make_pair(new RetainedDOMInfo(groupPair.first),
                                         std::move(groupChildren)));
     }
   }
 
   v8::HeapProfiler::RetainerEdges edges() { return std::move(m_edges); }
   v8::HeapProfiler::RetainerGroups groups() { return std::move(m_groups); }
 
+  void markWrappersInAllWorlds(
+      const ScriptWrappable* traceable) const override {
+    // Only mark the main thread wrapper as we cannot properly intercept
+    // DOMWrapperMap::markWrapper. This means that edges from the isolated
+    // worlds are missing in the snapshot.
+    traceable->markWrapper(this);
+  }
+
   void markWrapper(const v8::PersistentBase<v8::Value>* value) const override {
     if (m_currentParent && m_currentParent != value)
       m_edges.push_back(std::make_pair(m_currentParent, value));
     m_foundV8Wrappers.insert(value);
   }
 
   void dispatchTraceWrappers(const TraceWrapperBase* traceable) const override {
     if (!m_onlyTraceSingleLevel || !traceable->isScriptWrappable() ||
         !reinterpret_cast<const ScriptWrappable*>(traceable)
              ->containsWrapper() ||
@@ skipping 329 matching lines @@
   double startTime = WTF::currentTimeMS();
   v8::HandleScope scope(isolate);
   PendingActivityVisitor visitor(isolate, executionContext);
   toIsolate(executionContext)->VisitHandlesWithClassIds(&visitor);
   scanPendingActivityHistogram.count(
       static_cast<int>(WTF::currentTimeMS() - startTime));
   return visitor.pendingActivityFound();
 }
 
 }  // namespace blink