src: implement countObjectsWithPrototype

Author: joyeecheung

src/heap_utils.cc

@@ -38,6 +38,8 @@ using v8::Number;
 using v8::Object;
 using v8::ObjectTemplate;
 using v8::String;
+using v8::Symbol;
+using v8::TryCatch;
 using v8::Uint8Array;
 using v8::Value;
 
@@ -474,6 +476,40 @@ void TriggerHeapSnapshot(const FunctionCallbackInfo<Value>& args) {
   return args.GetReturnValue().Set(filename_v);
 }
 
+class PrototypeChainHas : public v8::QueryObjectPredicate {
+ public:
+  PrototypeChainHas(Local<Context> context, Local<Object> search)
+      : context_(context),
+        search_(search) {}
+
+  // What we can do in the filter can be quite limited, but looking up
+  // the prototype chain is something that the inspector console API
+  // queryObject() does so it is supported.
+  bool Filter(Local<Object> object) override {
+    for (Local<Value> proto = object->GetPrototype(); proto->IsObject();
+         proto = proto.As<Object>()->GetPrototype()) {
+      if (search_ == proto) return true;
+    }
+    return false;
+  }
+
+ private:
+  Local<Context> context_;
+  Local<Object> search_;
+};
+
+void CountObjectsWithPrototype(const FunctionCallbackInfo<Value>& args) {
+  CHECK_EQ(args.Length(), 1);
+  CHECK(args[0]->IsObject());
+  Local<Object> proto = args[0].As<Object>();
+  Isolate* isolate = args.GetIsolate();
+  Local<Context> context = isolate->GetCurrentContext();
+  PrototypeChainHas prototype_chain_has(context, proto);
+  std::vector<Global<Object>> out;
+  isolate->GetHeapProfiler()->QueryObjects(context, &prototype_chain_has, &out);
+  args.GetReturnValue().Set(static_cast<uint32_t>(out.size()));
+}
+
 void Initialize(Local<Object> target,
                 Local<Value> unused,
                 Local<Context> context,
@@ -482,12 +518,15 @@ void Initialize(Local<Object> target,
   SetMethod(context, target, "triggerHeapSnapshot", TriggerHeapSnapshot);
   SetMethod(
       context, target, "createHeapSnapshotStream", CreateHeapSnapshotStream);
+  SetMethod(
+      context, target, "countObjectsWithPrototype", CountObjectsWithPrototype);
 }
 
 void RegisterExternalReferences(ExternalReferenceRegistry* registry) {
   registry->Register(BuildEmbedderGraph);
   registry->Register(TriggerHeapSnapshot);
   registry->Register(CreateHeapSnapshotStream);
+  registry->Register(CountObjectsWithPrototype);
 }
 
 }  // namespace heap