src: make BuiltinLoader threadsafe and non-global

As discussed in #45888, using a
global `BuiltinLoader` instance is probably undesirable in a world
in which embedders are able to create Node.js Environments with
different sources and therefore mutually incompatible code
caching properties.

This PR makes it so that `BuiltinLoader` is no longer a global
singleton and instead only shared between `Environment`s that
have a direct relation to each other, and addresses a few
thread safety issues along with that.

Author: addaleax

src/api/environment.cc

@@ -458,9 +458,8 @@ MaybeLocal<Value> LoadEnvironment(
                                 main_script_source_utf8).ToLocalChecked();
         auto main_utf16 = std::make_unique<String::Value>(isolate, str);
 
-        // TODO(addaleax): Avoid having a global table for all scripts.
         std::string name = "embedder_main_" + std::to_string(env->thread_id());
-        builtins::BuiltinLoader::Add(
+        env->builtin_loader()->Add(
             name.c_str(), UnionBytes(**main_utf16, main_utf16->length()));
         env->set_main_utf16(std::move(main_utf16));
         Realm* realm = env->principal_realm();
@@ -703,9 +702,10 @@ Maybe<bool> InitializePrimordials(Local<Context> context) {
                                         "internal/per_context/messageport",
                                         nullptr};
 
+  auto builtin_loader = builtins::BuiltinLoader::Create();
   for (const char** module = context_files; *module != nullptr; module++) {
     Local<Value> arguments[] = {exports, primordials};
-    if (builtins::BuiltinLoader::CompileAndCall(
+    if (builtin_loader->CompileAndCall(
             context, *module, arraysize(arguments), arguments, nullptr)
             .IsEmpty()) {
       // Execution failed during context creation.

src/env-inl.h

@@ -432,6 +432,15 @@ inline std::vector<double>* Environment::destroy_async_id_list() {
   return &destroy_async_id_list_;
 }
 
+inline std::shared_ptr<builtins::BuiltinLoader> Environment::builtin_loader() {
+  DCHECK(builtin_loader_);
+  return builtin_loader_;
+}
+
+inline void Environment::set_builtin_loader(std::shared_ptr<builtins::BuiltinLoader> loader) {
+  builtin_loader_ = loader;
+}
+
 inline double Environment::new_async_id() {
   async_hooks()->async_id_fields()[AsyncHooks::kAsyncIdCounter] += 1;
   return async_hooks()->async_id_fields()[AsyncHooks::kAsyncIdCounter];

src/env.cc

@@ -747,6 +747,8 @@ Environment::Environment(IsolateData* isolate_data,
                   env_info,
                   flags,
                   thread_id) {
+  // TODO(addaleax): Make this part of CreateEnvironment().
+  set_builtin_loader(builtins::BuiltinLoader::Create());
   InitializeMainContext(context, env_info);
 }
 

src/env.h

@@ -716,6 +716,8 @@ class Environment : public MemoryRetainer {
   inline std::vector<double>* destroy_async_id_list();
 
   std::set<struct node_module*> internal_bindings;
+  std::shared_ptr<builtins::BuiltinLoader> builtin_loader();
+  void set_builtin_loader(std::shared_ptr<builtins::BuiltinLoader> loader);
   std::set<std::string> builtins_with_cache;
   std::set<std::string> builtins_without_cache;
   // This is only filled during deserialization. We use a vector since
@@ -1147,7 +1149,10 @@ class Environment : public MemoryRetainer {
   // Keeps the main script source alive is one was passed to LoadEnvironment().
   // We should probably find a way to just use plain `v8::String`s created from
   // the source passed to LoadEnvironment() directly instead.
+  // TODO(addaleax): Move this to BuiltinLoader, like we do for
+  // BuiltinLoader::AddExternalizedBuiltin().
   std::unique_ptr<v8::String::Value> main_utf16_;
+  std::shared_ptr<builtins::BuiltinLoader> builtin_loader_;
 
   // Used by allocate_managed_buffer() and release_managed_buffer() to keep
   // track of the BackingStore for a given pointer.

src/node.cc

@@ -1183,9 +1183,6 @@ ExitCode LoadSnapshotDataAndRun(const SnapshotData** snapshot_data_ptr,
     }
   }
 
-  if ((*snapshot_data_ptr) != nullptr) {
-    BuiltinLoader::RefreshCodeCache((*snapshot_data_ptr)->code_cache);
-  }
   NodeMainInstance main_instance(*snapshot_data_ptr,
                                  uv_default_loop(),
                                  per_process::v8_platform.Platform(),

src/node_binding.cc

@@ -586,13 +586,13 @@ void GetInternalBinding(const FunctionCallbackInfo<Value>& args) {
         exports->SetPrototype(env->context(), Null(env->isolate())).FromJust());
     DefineConstants(env->isolate(), exports);
   } else if (!strcmp(*module_v, "natives")) {
-    exports = builtins::BuiltinLoader::GetSourceObject(env->context());
+    exports = env->builtin_loader()->GetSourceObject(env->context());
     // Legacy feature: process.binding('natives').config contains stringified
     // config.gypi
     CHECK(exports
               ->Set(env->context(),
                     env->config_string(),
-                    builtins::BuiltinLoader::GetConfigString(env->isolate()))
+                    env->builtin_loader()->GetConfigString(env->isolate()))
               .FromJust());
   } else {
     return THROW_ERR_INVALID_MODULE(env, "No such binding: %s", *module_v);