fixup! fixup! fixup! fixup! fixup! src: make BuiltinLoader threadsafe and non-global

Author: addaleax

src/api/environment.cc

@@ -714,7 +714,12 @@ Maybe<bool> InitializePrimordials(Local<Context> context) {
                                         "internal/per_context/messageport",
                                         nullptr};
 
-  auto builtin_loader = builtins::BuiltinLoader::Create();
+  // We do not have access to a per-Environment BuiltinLoader instance
+  // at this point, because this code runs before an Environment exists
+  // in the first place. However, creating BuiltinLoader instances is
+  // relatively cheap and all the scripts that we may want to run at
+  // startup are always present in it.
+  thread_local auto builtin_loader = builtins::BuiltinLoader::Create();
   for (const char** module = context_files; *module != nullptr; module++) {
     Local<Value> arguments[] = {exports, primordials};
     if (builtin_loader

src/node_builtins.cc

@@ -563,7 +563,6 @@ void BuiltinLoader::GetBuiltinCategories(
   Local<Context> context = env->context();
   Local<Object> result = Object::New(isolate);
 
-  // Copy from the per-process categories
   std::set<std::string> cannot_be_required =
       env->builtin_loader()->GetCannotBeRequired();
   std::set<std::string> can_be_required =