sea: return the SEA resource by reference

FindSingleExecutableResource() returned the deserialized SeaResource by
value, copying the whole assets map on every call. getAsset() calls it
once per asset read, which made every fs operation served by the SEA
virtual file system pay a cost linear in the number of bundled assets:
with 8192 assets, reading each of them took seconds instead of
milliseconds. Return a reference to the cached resource instead.

Signed-off-by: Matteo Collina <hello@matteocollina.com>

Author: mcollina

src/module_wrap.cc

@@ -367,7 +367,7 @@ void ModuleWrap::New(const FunctionCallbackInfo<Value>& args) {
       // For embedder ESM in a SEA, use the bundled code cache if available.
       if (id_symbol == realm->isolate_data()->embedder_module_hdo() &&
           sea::IsSingleExecutable()) {
-        sea::SeaResource sea = sea::FindSingleExecutableResource();
+        const sea::SeaResource& sea = sea::FindSingleExecutableResource();
         if (sea.use_code_cache()) {
           std::string_view data = sea.code_cache.value();
           user_cached_data = new ScriptCompiler::CachedData(

src/node.cc

@@ -330,7 +330,7 @@ MaybeLocal<Value> StartExecution(Environment* env,
 #ifndef DISABLE_SINGLE_EXECUTABLE_APPLICATION
   // Snapshot in SEA is only loaded for the main thread.
   if (sea::IsSingleExecutable() && env->is_main_thread()) {
-    sea::SeaResource sea = sea::FindSingleExecutableResource();
+    const sea::SeaResource& sea = sea::FindSingleExecutableResource();
     // The SEA preparation blob building process should already enforce this,
     // this check is just here to guard against the unlikely case where
     // the SEA preparation blob has been manually modified by someone.
@@ -976,7 +976,7 @@ static ExitCode InitializeNodeWithArgsInternal(
       !(flags & ProcessInitializationFlags::kDisableNodeOptionsEnv);
 #ifndef DISABLE_SINGLE_EXECUTABLE_APPLICATION
   if (sea::IsSingleExecutable()) {
-    sea::SeaResource sea_resource = sea::FindSingleExecutableResource();
+    const sea::SeaResource& sea_resource = sea::FindSingleExecutableResource();
     if (sea_resource.exec_argv_extension != sea::SeaExecArgvExtension::kEnv) {
       should_parse_node_options = false;
     }
@@ -1562,7 +1562,7 @@ bool LoadSnapshotData(const SnapshotData** snapshot_data_ptr) {
 #ifndef DISABLE_SINGLE_EXECUTABLE_APPLICATION
   if (sea::IsSingleExecutable()) {
     is_sea = true;
-    sea::SeaResource sea = sea::FindSingleExecutableResource();
+    const sea::SeaResource& sea = sea::FindSingleExecutableResource();
     if (sea.use_snapshot()) {
       std::unique_ptr<SnapshotData> read_data =
           std::make_unique<SnapshotData>();

src/node_contextify.cc

@@ -1768,7 +1768,7 @@ static void CompileFunctionForCJSLoader(
   ScriptCompiler::CachedData* cached_data = nullptr;
 #ifndef DISABLE_SINGLE_EXECUTABLE_APPLICATION
   if (is_sea_main) {
-    sea::SeaResource sea = sea::FindSingleExecutableResource();
+    const sea::SeaResource& sea = sea::FindSingleExecutableResource();
     // Use the "main" field in SEA config for the filename.
     Local<Value> filename_from_sea;
     if (!ToV8Value(context, sea.code_path).ToLocal(&filename_from_sea)) {

src/node_sea.cc

@@ -246,7 +246,7 @@ bool SeaResource::use_code_cache() const {
   return static_cast<bool>(flags & SeaFlags::kUseCodeCache);
 }
 
-SeaResource FindSingleExecutableResource() {
+const SeaResource& FindSingleExecutableResource() {
   static const SeaResource sea_resource = []() -> SeaResource {
     std::string_view blob = FindSingleExecutableBlob();
     per_process::Debug(DebugCategory::SEA,
@@ -266,7 +266,7 @@ void IsSea(const FunctionCallbackInfo<Value>& args) {
 void IsVfsEnabled(const FunctionCallbackInfo<Value>& args) {
   bool enabled = false;
   if (IsSingleExecutable()) {
-    SeaResource sea_resource = FindSingleExecutableResource();
+    const SeaResource& sea_resource = FindSingleExecutableResource();
     enabled = static_cast<bool>(sea_resource.flags & SeaFlags::kEnableVfs);
   }
   args.GetReturnValue().Set(enabled);
@@ -285,7 +285,7 @@ void IsExperimentalSeaWarningNeeded(const FunctionCallbackInfo<Value>& args) {
     return;
   }
 
-  SeaResource sea_resource = FindSingleExecutableResource();
+  const SeaResource& sea_resource = FindSingleExecutableResource();
   args.GetReturnValue().Set(!static_cast<bool>(
       sea_resource.flags & SeaFlags::kDisableExperimentalSeaWarning));
 }
@@ -300,7 +300,7 @@ std::tuple<int, char**> FixupArgsForSEA(int argc,
     static std::vector<std::string> exec_argv_storage;
     static std::vector<std::string> cli_extension_args;
 
-    SeaResource sea_resource = FindSingleExecutableResource();
+    const SeaResource& sea_resource = FindSingleExecutableResource();
 
     new_argv.clear();
     exec_argv_storage.clear();
@@ -868,7 +868,7 @@ void GetAsset(const FunctionCallbackInfo<Value>& args) {
   CHECK_EQ(args.Length(), 1);
   CHECK(args[0]->IsString());
   Utf8Value key(args.GetIsolate(), args[0]);
-  SeaResource sea_resource = FindSingleExecutableResource();
+  const SeaResource& sea_resource = FindSingleExecutableResource();
   if (sea_resource.assets.empty()) {
     return;
   }
@@ -892,7 +892,7 @@ void GetAsset(const FunctionCallbackInfo<Value>& args) {
 void GetAssetKeys(const FunctionCallbackInfo<Value>& args) {
   CHECK_EQ(args.Length(), 0);
   Isolate* isolate = args.GetIsolate();
-  SeaResource sea_resource = FindSingleExecutableResource();
+  const SeaResource& sea_resource = FindSingleExecutableResource();
 
   Local<Context> context = isolate->GetCurrentContext();
   LocalVector<Value> keys(isolate);
@@ -914,7 +914,7 @@ MaybeLocal<Value> LoadSingleExecutableApplication(
   // env->context() is entered.
   Environment* env = info.env();
   Local<Context> context = env->context();
-  SeaResource sea = FindSingleExecutableResource();
+  const SeaResource& sea = FindSingleExecutableResource();
 
   CHECK(!sea.use_snapshot());
   // TODO(joyeecheung): this should be an external string. Refactor UnionBytes
@@ -936,7 +936,7 @@ bool MaybeLoadSingleExecutableApplication(Environment* env) {
     return false;
   }
 
-  SeaResource sea = FindSingleExecutableResource();
+  const SeaResource& sea = FindSingleExecutableResource();
 
   if (sea.use_snapshot()) {
     // The SEA preparation blob building process should already enforce this,
@@ -962,7 +962,7 @@ void Initialize(Local<Object> target,
   Isolate* isolate = env->isolate();
 
   if (IsSingleExecutable()) {
-    SeaResource sea_resource = FindSingleExecutableResource();
+    const SeaResource& sea_resource = FindSingleExecutableResource();
     // Expose the main script path recorded in the SEA config so the VFS
     // integration can place the main script at the mount point root.
     if (static_cast<bool>(sea_resource.flags & SeaFlags::kEnableVfs)) {

src/node_sea.h

@@ -70,7 +70,7 @@ struct SeaResource {
 
 bool IsSingleExecutable();
 std::string_view FindSingleExecutableBlob();
-SeaResource FindSingleExecutableResource();
+const SeaResource& FindSingleExecutableResource();
 std::tuple<int, char**> FixupArgsForSEA(int argc,
                                         char** argv,
                                         std::vector<std::string>* errors);