src: create BaseObject with node::Realm

BaseObject is a wrapper around JS objects. These objects should be
created in a node::Realm and destroyed when their associated realm is
cleaning up.

PR-URL: #44348
Refs: #42528
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

node.gyp

@@ -477,6 +477,7 @@
         'src/api/hooks.cc',
         'src/api/utils.cc',
         'src/async_wrap.cc',
+        'src/base_object.cc',
         'src/cares_wrap.cc',
         'src/cleanup_queue.cc',
         'src/connect_wrap.cc',

src/api/embed_helpers.cc

@@ -68,7 +68,7 @@ Maybe<int> SpinEventLoop(Environment* env) {
   env->set_snapshot_serialize_callback(Local<Function>());
 
   env->PrintInfoForSnapshotIfDebug();
-  env->VerifyNoStrongBaseObjects();
+  env->ForEachRealm([](Realm* realm) { realm->VerifyNoStrongBaseObjects(); });
   return EmitProcessExit(env);
 }
 

src/base_object-inl.h

@@ -32,6 +32,9 @@
 
 namespace node {
 
+BaseObject::BaseObject(Environment* env, v8::Local<v8::Object> object)
+    : BaseObject(env->principal_realm(), object) {}
+
 // static
 v8::Local<v8::FunctionTemplate> BaseObject::GetConstructorTemplate(
     Environment* env) {
@@ -63,7 +66,11 @@ v8::Local<v8::Object> BaseObject::object(v8::Isolate* isolate) const {
 }
 
 Environment* BaseObject::env() const {
-  return env_;
+  return realm_->env();
+}
+
+Realm* BaseObject::realm() const {
+  return realm_;
 }
 
 BaseObject* BaseObject::FromJSObject(v8::Local<v8::Value> value) {

src/base_object.cc

@@ -0,0 +1,164 @@
+#include "base_object.h"
+#include "env-inl.h"
+#include "node_realm-inl.h"
+
+namespace node {
+
+using v8::FunctionCallbackInfo;
+using v8::FunctionTemplate;
+using v8::HandleScope;
+using v8::Local;
+using v8::Object;
+using v8::Value;
+using v8::WeakCallbackInfo;
+using v8::WeakCallbackType;
+
+BaseObject::BaseObject(Realm* realm, Local<Object> object)
+    : persistent_handle_(realm->isolate(), object), realm_(realm) {
+  CHECK_EQ(false, object.IsEmpty());
+  CHECK_GE(object->InternalFieldCount(), BaseObject::kInternalFieldCount);
+  object->SetAlignedPointerInInternalField(BaseObject::kEmbedderType,
+                                           &kNodeEmbedderId);
+  object->SetAlignedPointerInInternalField(BaseObject::kSlot,
+                                           static_cast<void*>(this));
+  realm->AddCleanupHook(DeleteMe, static_cast<void*>(this));
+  realm->modify_base_object_count(1);
+}
+
+BaseObject::~BaseObject() {
+  realm()->modify_base_object_count(-1);
+  realm()->RemoveCleanupHook(DeleteMe, static_cast<void*>(this));
+
+  if (UNLIKELY(has_pointer_data())) {
+    PointerData* metadata = pointer_data();
+    CHECK_EQ(metadata->strong_ptr_count, 0);
+    metadata->self = nullptr;
+    if (metadata->weak_ptr_count == 0) delete metadata;
+  }
+
+  if (persistent_handle_.IsEmpty()) {
+    // This most likely happened because the weak callback below cleared it.
+    return;
+  }
+
+  {
+    HandleScope handle_scope(realm()->isolate());
+    object()->SetAlignedPointerInInternalField(BaseObject::kSlot, nullptr);
+  }
+}
+
+void BaseObject::MakeWeak() {
+  if (has_pointer_data()) {
+    pointer_data()->wants_weak_jsobj = true;
+    if (pointer_data()->strong_ptr_count > 0) return;
+  }
+
+  persistent_handle_.SetWeak(
+      this,
+      [](const WeakCallbackInfo<BaseObject>& data) {
+        BaseObject* obj = data.GetParameter();
+        // Clear the persistent handle so that ~BaseObject() doesn't attempt
+        // to mess with internal fields, since the JS object may have
+        // transitioned into an invalid state.
+        // Refs: https://github.com/nodejs/node/issues/18897
+        obj->persistent_handle_.Reset();
+        CHECK_IMPLIES(obj->has_pointer_data(),
+                      obj->pointer_data()->strong_ptr_count == 0);
+        obj->OnGCCollect();
+      },
+      WeakCallbackType::kParameter);
+}
+
+// This just has to be different from the Chromium ones:
+// https://source.chromium.org/chromium/chromium/src/+/main:gin/public/gin_embedders.h;l=18-23;drc=5a758a97032f0b656c3c36a3497560762495501a
+// Otherwise, when Node is loaded in an isolate which uses cppgc, cppgc will
+// misinterpret the data stored in the embedder fields and try to garbage
+// collect them.
+uint16_t kNodeEmbedderId = 0x90de;
+
+void BaseObject::LazilyInitializedJSTemplateConstructor(
+    const FunctionCallbackInfo<Value>& args) {
+  DCHECK(args.IsConstructCall());
+  CHECK_GE(args.This()->InternalFieldCount(), BaseObject::kInternalFieldCount);
+  args.This()->SetAlignedPointerInInternalField(BaseObject::kEmbedderType,
+                                                &kNodeEmbedderId);
+  args.This()->SetAlignedPointerInInternalField(BaseObject::kSlot, nullptr);
+}
+
+Local<FunctionTemplate> BaseObject::MakeLazilyInitializedJSTemplate(
+    Environment* env) {
+  Local<FunctionTemplate> t = NewFunctionTemplate(
+      env->isolate(), LazilyInitializedJSTemplateConstructor);
+  t->Inherit(BaseObject::GetConstructorTemplate(env));
+  t->InstanceTemplate()->SetInternalFieldCount(BaseObject::kInternalFieldCount);
+  return t;
+}
+
+BaseObject::PointerData* BaseObject::pointer_data() {
+  if (!has_pointer_data()) {
+    PointerData* metadata = new PointerData();
+    metadata->wants_weak_jsobj = persistent_handle_.IsWeak();
+    metadata->self = this;
+    pointer_data_ = metadata;
+  }
+  CHECK(has_pointer_data());
+  return pointer_data_;
+}
+
+void BaseObject::decrease_refcount() {
+  CHECK(has_pointer_data());
+  PointerData* metadata = pointer_data();
+  CHECK_GT(metadata->strong_ptr_count, 0);
+  unsigned int new_refcount = --metadata->strong_ptr_count;
+  if (new_refcount == 0) {
+    if (metadata->is_detached) {
+      OnGCCollect();
+    } else if (metadata->wants_weak_jsobj && !persistent_handle_.IsEmpty()) {
+      MakeWeak();
+    }
+  }
+}
+
+void BaseObject::increase_refcount() {
+  unsigned int prev_refcount = pointer_data()->strong_ptr_count++;
+  if (prev_refcount == 0 && !persistent_handle_.IsEmpty())
+    persistent_handle_.ClearWeak();
+}
+
+void BaseObject::DeleteMe(void* data) {
+  BaseObject* self = static_cast<BaseObject*>(data);
+  if (self->has_pointer_data() && self->pointer_data()->strong_ptr_count > 0) {
+    return self->Detach();
+  }
+  delete self;
+}
+
+bool BaseObject::IsDoneInitializing() const {
+  return true;
+}
+
+Local<Object> BaseObject::WrappedObject() const {
+  return object();
+}
+
+bool BaseObject::IsRootNode() const {
+  return !persistent_handle_.IsWeak();
+}
+
+Local<FunctionTemplate> BaseObject::GetConstructorTemplate(
+    IsolateData* isolate_data) {
+  Local<FunctionTemplate> tmpl = isolate_data->base_object_ctor_template();
+  if (tmpl.IsEmpty()) {
+    tmpl = NewFunctionTemplate(isolate_data->isolate(), nullptr);
+    tmpl->SetClassName(
+        FIXED_ONE_BYTE_STRING(isolate_data->isolate(), "BaseObject"));
+    isolate_data->set_base_object_ctor_template(tmpl);
+  }
+  return tmpl;
+}
+
+bool BaseObject::IsNotIndicativeOfMemoryLeakAtExit() const {
+  return IsWeakOrDetached();
+}
+
+}  // namespace node

src/base_object.h

@@ -32,6 +32,7 @@ namespace node {
 
 class Environment;
 class IsolateData;
+class Realm;
 template <typename T, bool kIsWeak>
 class BaseObjectPtrImpl;
 
@@ -47,7 +48,10 @@ class BaseObject : public MemoryRetainer {
 
   // Associates this object with `object`. It uses the 1st internal field for
   // that, and in particular aborts if there is no such field.
-  BaseObject(Environment* env, v8::Local<v8::Object> object);
+  // This is the designated constructor.
+  BaseObject(Realm* realm, v8::Local<v8::Object> object);
+  // Convenient constructor for constructing BaseObject in the principal realm.
+  inline BaseObject(Environment* env, v8::Local<v8::Object> object);
   ~BaseObject() override;
 
   BaseObject() = delete;
@@ -63,6 +67,7 @@ class BaseObject : public MemoryRetainer {
   inline v8::Global<v8::Object>& persistent();
 
   inline Environment* env() const;
+  inline Realm* realm() const;
 
   // Get a BaseObject* pointer, or subclass pointer, for the JS object that
   // was also passed to the `BaseObject()` constructor initially.
@@ -93,6 +98,7 @@ class BaseObject : public MemoryRetainer {
   // Utility to create a FunctionTemplate with one internal field (used for
   // the `BaseObject*` pointer) and a constructor that initializes that field
   // to `nullptr`.
+  // TODO(legendecas): Disentangle template with env.
   static v8::Local<v8::FunctionTemplate> MakeLazilyInitializedJSTemplate(
       Environment* env);
 
@@ -215,7 +221,7 @@ class BaseObject : public MemoryRetainer {
   void decrease_refcount();
   void increase_refcount();
 
-  Environment* env_;
+  Realm* realm_;
   PointerData* pointer_data_ = nullptr;
 };
 

src/env-inl.h

@@ -745,6 +745,12 @@ inline IsolateData* Environment::isolate_data() const {
   return isolate_data_;
 }
 
+template <typename T>
+inline void Environment::ForEachRealm(T&& iterator) const {
+  // TODO(legendecas): iterate over more realms bound to the environment.
+  iterator(principal_realm());
+}
+
 inline void Environment::ThrowError(const char* errmsg) {
   ThrowError(v8::Exception::Error, errmsg);
 }
@@ -789,27 +795,6 @@ void Environment::RemoveCleanupHook(CleanupQueue::Callback fn, void* arg) {
   cleanup_queue_.Remove(fn, arg);
 }
 
-template <typename T>
-void Environment::ForEachBaseObject(T&& iterator) {
-  cleanup_queue_.ForEachBaseObject(std::forward<T>(iterator));
-}
-
-void Environment::modify_base_object_count(int64_t delta) {
-  base_object_count_ += delta;
-}
-
-int64_t Environment::base_object_count() const {
-  return base_object_count_;
-}
-
-inline void Environment::set_base_object_created_by_bootstrap(int64_t count) {
-  base_object_created_by_bootstrap_ = base_object_count_;
-}
-
-int64_t Environment::base_object_created_after_bootstrap() const {
-  return base_object_count_ - base_object_created_by_bootstrap_;
-}
-
 void Environment::set_main_utf16(std::unique_ptr<v8::String::Value> str) {
   CHECK(!main_utf16_);
   main_utf16_ = std::move(str);