src: do not track BaseObjects via cleanup hooks

Since f59ec2a, `BaseObject` instances were tracked in heap snapshots
through their associated `CleanupHookCallback`s which were stored on
the `Environment`; however, this is inaccurate, because:

- Edges in heap dumps imply a keeps-alive relationship, but cleanup
  hooks do not keep the `BaseObject`s that they point to alive.
- It loses information about whether `BaseObject` instances are
  GC roots: Even weak `BaseObject`s are now, practically speaking,
  showing up as hanging off a GC root when that isn’t actually the case
  (e.g. in the description of #33468).

Thus, this is a partial revert of f59ec2a.

Refs: #33468
Refs: #27018

PR-URL: #33809
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>

Author: addaleax

src/base_object.h

@@ -103,6 +103,7 @@ class BaseObject : public MemoryRetainer {
 
  private:
   v8::Local<v8::Object> WrappedObject() const override;
+  bool IsRootNode() const override;
   static void DeleteMe(void* data);
 
   // persistent_handle_ needs to be at a fixed offset from the start of the

src/env.cc

@@ -986,33 +986,16 @@ Environment* Environment::worker_parent_env() const {
   return worker_context_->env();
 }
 
-void MemoryTracker::TrackField(const char* edge_name,
-                               const CleanupHookCallback& value,
-                               const char* node_name) {
-  HandleScope handle_scope(isolate_);
-  // Here, we utilize the fact that CleanupHookCallback instances
-  // are all unique and won't be tracked twice in one BuildEmbedderGraph
-  // callback.
-  MemoryRetainerNode* n =
-      PushNode("CleanupHookCallback", sizeof(value), edge_name);
-  // TODO(joyeecheung): at the moment only arguments of type BaseObject will be
-  // identified and tracked here (based on their deleters),
-  // but we may convert and track other known types here.
-  BaseObject* obj = value.GetBaseObject();
-  if (obj != nullptr && obj->IsDoneInitializing()) {
-    TrackField("arg", obj);
-  }
-  CHECK_EQ(CurrentNode(), n);
-  CHECK_NE(n->size_, 0);
-  PopNode();
-}
-
 void Environment::BuildEmbedderGraph(Isolate* isolate,
                                      EmbedderGraph* graph,
                                      void* data) {
   MemoryTracker tracker(isolate, graph);
   Environment* env = static_cast<Environment*>(data);
   tracker.Track(env);
+  env->ForEachBaseObject([&](BaseObject* obj) {
+    if (obj->IsDoneInitializing())
+      tracker.Track(obj);
+  });
 }
 
 inline size_t Environment::SelfSize() const {
@@ -1042,7 +1025,8 @@ void Environment::MemoryInfo(MemoryTracker* tracker) const {
   tracker->TrackField("fs_stats_field_array", fs_stats_field_array_);
   tracker->TrackField("fs_stats_field_bigint_array",
                       fs_stats_field_bigint_array_);
-  tracker->TrackField("cleanup_hooks", cleanup_hooks_);
+  tracker->TrackFieldWithSize(
+      "cleanup_hooks", cleanup_hooks_.size() * sizeof(CleanupHookCallback));
   tracker->TrackField("async_hooks", async_hooks_);
   tracker->TrackField("immediate_info", immediate_info_);
   tracker->TrackField("tick_info", tick_info_);
@@ -1136,4 +1120,8 @@ Local<Object> BaseObject::WrappedObject() const {
   return object();
 }
 
+bool BaseObject::IsRootNode() const {
+  return !persistent_handle_.IsWeak();
+}
+
 }  // namespace node

src/memory_tracker.h

@@ -208,13 +208,6 @@ class MemoryTracker {
   inline void TrackField(const char* edge_name,
                          const MallocedBuffer<T>& value,
                          const char* node_name = nullptr);
-  // We do not implement CleanupHookCallback as MemoryRetainer
-  // but instead specialize the method here to avoid the cost of
-  // virtual pointers.
-  // TODO(joyeecheung): do this for BaseObject and remove WrappedObject()
-  void TrackField(const char* edge_name,
-                  const CleanupHookCallback& value,
-                  const char* node_name = nullptr);
   inline void TrackField(const char* edge_name,
                          const uv_buf_t& value,
                          const char* node_name = nullptr);

test/pummel/test-heapdump-env.js

@@ -5,7 +5,6 @@
 
 require('../common');
 const { validateSnapshotNodes } = require('../common/heap');
-const assert = require('assert');
 
 // This is just using ContextifyScript as an example here, it can be replaced
 // with any BaseObject that we can easily instantiate here and register in
@@ -16,51 +15,10 @@ const context = require('vm').createScript('const foo = 123');
 
 validateSnapshotNodes('Node / Environment', [{
   children: [
-    cleanupHooksFilter,
     { node_name: 'Node / cleanup_hooks', edge_name: 'cleanup_hooks' },
     { node_name: 'process', edge_name: 'process_object' },
     { node_name: 'Node / IsolateData', edge_name: 'isolate_data' },
   ]
 }]);
 
-function cleanupHooksFilter(edge) {
-  if (edge.name !== 'cleanup_hooks') {
-    return false;
-  }
-  if (edge.to.type === 'native') {
-    verifyCleanupHooksInSnapshot(edge.to);
-  } else {
-    verifyCleanupHooksInGraph(edge.to);
-  }
-  return true;
-}
-
-function verifyCleanupHooksInSnapshot(node) {
-  assert.strictEqual(node.name, 'Node / cleanup_hooks');
-  const baseObjects = [];
-  for (const hook of node.outgoingEdges) {
-    for (const hookEdge of hook.to.outgoingEdges) {
-      if (hookEdge.name === 'arg') {
-        baseObjects.push(hookEdge.to);
-      }
-    }
-  }
-  // Make sure our ContextifyScript show up.
-  assert(baseObjects.some((node) => node.name === 'Node / ContextifyScript'));
-}
-
-function verifyCleanupHooksInGraph(node) {
-  assert.strictEqual(node.name, 'Node / cleanup_hooks');
-  const baseObjects = [];
-  for (const hook of node.edges) {
-    for (const hookEdge of hook.to.edges) {
-      if (hookEdge.name === 'arg') {
-        baseObjects.push(hookEdge.to);
-      }
-    }
-  }
-  // Make sure our ContextifyScript show up.
-  assert(baseObjects.some((node) => node.name === 'Node / ContextifyScript'));
-}
-
 console.log(context);  // Make sure it's not GC'ed