src: allow snapshotting from the embedder API

PR-URL: #45888
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>

Author: addaleax

lib/internal/main/mksnapshot.js

@@ -12,6 +12,7 @@ const {
 const binding = internalBinding('mksnapshot');
 const { BuiltinModule } = require('internal/bootstrap/loaders');
 const {
+  getEmbedderEntryFunction,
   compileSerializeMain,
 } = binding;
 
@@ -119,14 +120,21 @@ function main() {
     prepareMainThreadExecution
   } = require('internal/process/pre_execution');
 
-  prepareMainThreadExecution(true, false);
+  let serializeMainFunction = getEmbedderEntryFunction();
+  const serializeMainArgs = [requireForUserSnapshot];
 
-  const file = process.argv[1];
-  const path = require('path');
-  const filename = path.resolve(file);
-  const dirname = path.dirname(filename);
-  const source = readFileSync(file, 'utf-8');
-  const serializeMainFunction = compileSerializeMain(filename, source);
+  if (serializeMainFunction) { // embedded case
+    prepareMainThreadExecution(false, false);
+  } else {
+    prepareMainThreadExecution(true, false);
+    const file = process.argv[1];
+    const path = require('path');
+    const filename = path.resolve(file);
+    const dirname = path.dirname(filename);
+    const source = readFileSync(file, 'utf-8');
+    serializeMainFunction = compileSerializeMain(filename, source);
+    serializeMainArgs.push(filename, dirname);
+  }
 
   const {
     initializeCallbacks,
@@ -146,10 +154,9 @@ function main() {
 
   if (getOptionValue('--inspect-brk')) {
     internalBinding('inspector').callAndPauseOnStart(
-      serializeMainFunction, undefined,
-      requireForUserSnapshot, filename, dirname);
+      serializeMainFunction, undefined, ...serializeMainArgs);
   } else {
-    serializeMainFunction(requireForUserSnapshot, filename, dirname);
+    serializeMainFunction(...serializeMainArgs);
   }
 
   addSerializeCallback(() => {

src/api/embed_helpers.cc

@@ -14,6 +14,7 @@ using v8::Locker;
 using v8::Maybe;
 using v8::Nothing;
 using v8::SealHandleScope;
+using v8::SnapshotCreator;
 
 namespace node {
 
@@ -78,16 +79,18 @@ struct CommonEnvironmentSetup::Impl {
   MultiIsolatePlatform* platform = nullptr;
   uv_loop_t loop;
   std::shared_ptr<ArrayBufferAllocator> allocator;
+  std::optional<SnapshotCreator> snapshot_creator;
   Isolate* isolate = nullptr;
   DeleteFnPtr<IsolateData, FreeIsolateData> isolate_data;
   DeleteFnPtr<Environment, FreeEnvironment> env;
-  Global<Context> context;
+  Global<Context> main_context;
 };
 
 CommonEnvironmentSetup::CommonEnvironmentSetup(
     MultiIsolatePlatform* platform,
     std::vector<std::string>* errors,
     const EmbedderSnapshotData* snapshot_data,
+    uint32_t flags,
     std::function<Environment*(const CommonEnvironmentSetup*)> make_env)
     : impl_(new Impl()) {
   CHECK_NOT_NULL(platform);
@@ -105,28 +108,43 @@ CommonEnvironmentSetup::CommonEnvironmentSetup(
   }
   loop->data = this;
 
-  impl_->allocator = ArrayBufferAllocator::Create();
-  impl_->isolate =
-      NewIsolate(impl_->allocator, &impl_->loop, platform, snapshot_data);
-  Isolate* isolate = impl_->isolate;
+  Isolate* isolate;
+  if (flags & Flags::kIsForSnapshotting) {
+    const std::vector<intptr_t>& external_references =
+        SnapshotBuilder::CollectExternalReferences();
+    isolate = impl_->isolate = Isolate::Allocate();
+    // Must be done before the SnapshotCreator creation so  that the
+    // memory reducer can be initialized.
+    platform->RegisterIsolate(isolate, loop);
+    impl_->snapshot_creator.emplace(isolate, external_references.data());
+    isolate->SetCaptureStackTraceForUncaughtExceptions(
+        true, 10, v8::StackTrace::StackTraceOptions::kDetailed);
+    SetIsolateMiscHandlers(isolate, {});
+  } else {
+    impl_->allocator = ArrayBufferAllocator::Create();
+    isolate = impl_->isolate =
+        NewIsolate(impl_->allocator, &impl_->loop, platform, snapshot_data);
+  }
 
   {
     Locker locker(isolate);
     Isolate::Scope isolate_scope(isolate);
     impl_->isolate_data.reset(CreateIsolateData(
         isolate, loop, platform, impl_->allocator.get(), snapshot_data));
+    impl_->isolate_data->options()->build_snapshot =
+        impl_->snapshot_creator.has_value();
 
     HandleScope handle_scope(isolate);
     if (snapshot_data) {
       impl_->env.reset(make_env(this));
       if (impl_->env) {
-        impl_->context.Reset(isolate, impl_->env->context());
+        impl_->main_context.Reset(isolate, impl_->env->context());
       }
       return;
     }
 
     Local<Context> context = NewContext(isolate);
-    impl_->context.Reset(isolate, context);
+    impl_->main_context.Reset(isolate, context);
     if (context.IsEmpty()) {
       errors->push_back("Failed to initialize V8 Context");
       return;
@@ -141,7 +159,37 @@ CommonEnvironmentSetup::CommonEnvironmentSetup(
     MultiIsolatePlatform* platform,
     std::vector<std::string>* errors,
     std::function<Environment*(const CommonEnvironmentSetup*)> make_env)
-    : CommonEnvironmentSetup(platform, errors, nullptr, make_env) {}
+    : CommonEnvironmentSetup(platform, errors, nullptr, false, make_env) {}
+
+std::unique_ptr<CommonEnvironmentSetup>
+CommonEnvironmentSetup::CreateForSnapshotting(
+    MultiIsolatePlatform* platform,
+    std::vector<std::string>* errors,
+    const std::vector<std::string>& args,
+    const std::vector<std::string>& exec_args) {
+  // It's not guaranteed that a context that goes through
+  // v8_inspector::V8Inspector::contextCreated() is runtime-independent,
+  // so do not start the inspector on the main context when building
+  // the default snapshot.
+  uint64_t env_flags =
+      EnvironmentFlags::kDefaultFlags | EnvironmentFlags::kNoCreateInspector;
+
+  auto ret = std::unique_ptr<CommonEnvironmentSetup>(new CommonEnvironmentSetup(
+      platform,
+      errors,
+      nullptr,
+      true,
+      [&](const CommonEnvironmentSetup* setup) -> Environment* {
+        return CreateEnvironment(
+            setup->isolate_data(),
+            setup->context(),
+            args,
+            exec_args,
+            static_cast<EnvironmentFlags::Flags>(env_flags));
+      }));
+  if (!errors->empty()) ret.reset();
+  return ret;
+}
 
 CommonEnvironmentSetup::~CommonEnvironmentSetup() {
   if (impl_->isolate != nullptr) {
@@ -150,7 +198,7 @@ CommonEnvironmentSetup::~CommonEnvironmentSetup() {
       Locker locker(isolate);
       Isolate::Scope isolate_scope(isolate);
 
-      impl_->context.Reset();
+      impl_->main_context.Reset();
       impl_->env.reset();
       impl_->isolate_data.reset();
     }
@@ -160,7 +208,10 @@ CommonEnvironmentSetup::~CommonEnvironmentSetup() {
       *static_cast<bool*>(data) = true;
     }, &platform_finished);
     impl_->platform->UnregisterIsolate(isolate);
-    isolate->Dispose();
+    if (impl_->snapshot_creator.has_value())
+      impl_->snapshot_creator.reset();
+    else
+      isolate->Dispose();
 
     // Wait until the platform has cleaned up all relevant resources.
     while (!platform_finished)
@@ -173,6 +224,21 @@ CommonEnvironmentSetup::~CommonEnvironmentSetup() {
   delete impl_;
 }
 
+EmbedderSnapshotData::Pointer CommonEnvironmentSetup::CreateSnapshot() {
+  CHECK_NOT_NULL(snapshot_creator());
+  SnapshotData* snapshot_data = new SnapshotData();
+  EmbedderSnapshotData::Pointer result{
+      new EmbedderSnapshotData(snapshot_data, true)};
+
+  auto exit_code = SnapshotBuilder::CreateSnapshot(
+      snapshot_data,
+      this,
+      static_cast<uint8_t>(SnapshotMetadata::Type::kFullyCustomized));
+  if (exit_code != ExitCode::kNoFailure) return {};
+
+  return result;
+}
+
 Maybe<int> SpinEventLoop(Environment* env) {
   Maybe<ExitCode> result = SpinEventLoopInternal(env);
   if (result.IsNothing()) {
@@ -203,7 +269,11 @@ Environment* CommonEnvironmentSetup::env() const {
 }
 
 v8::Local<v8::Context> CommonEnvironmentSetup::context() const {
-  return impl_->context.Get(impl_->isolate);
+  return impl_->main_context.Get(impl_->isolate);
+}
+
+v8::SnapshotCreator* CommonEnvironmentSetup::snapshot_creator() {
+  return impl_->snapshot_creator ? &impl_->snapshot_creator.value() : nullptr;
 }
 
 void EmbedderSnapshotData::DeleteSnapshotData::operator()(
@@ -232,6 +302,10 @@ EmbedderSnapshotData::Pointer EmbedderSnapshotData::FromFile(FILE* in) {
   return result;
 }
 
+void EmbedderSnapshotData::ToFile(FILE* out) const {
+  impl_->ToBlob(out);
+}
+
 EmbedderSnapshotData::EmbedderSnapshotData(const SnapshotData* impl,
                                            bool owns_impl)
     : impl_(impl), owns_impl_(owns_impl) {}

src/env-inl.h

@@ -444,6 +444,16 @@ inline builtins::BuiltinLoader* Environment::builtin_loader() {
   return &builtin_loader_;
 }
 
+inline const StartExecutionCallback&
+Environment::embedder_mksnapshot_entry_point() const {
+  return embedder_mksnapshot_entry_point_;
+}
+
+inline void Environment::set_embedder_mksnapshot_entry_point(
+    StartExecutionCallback&& fn) {
+  embedder_mksnapshot_entry_point_ = std::move(fn);
+}
+
 inline double Environment::new_async_id() {
   async_hooks()->async_id_fields()[AsyncHooks::kAsyncIdCounter] += 1;
   return async_hooks()->async_id_fields()[AsyncHooks::kAsyncIdCounter];

src/env.h

@@ -961,6 +961,9 @@ class Environment : public MemoryRetainer {
 
 #endif  // HAVE_INSPECTOR
 
+  inline const StartExecutionCallback& embedder_mksnapshot_entry_point() const;
+  inline void set_embedder_mksnapshot_entry_point(StartExecutionCallback&& fn);
+
   inline void set_process_exit_handler(
       std::function<void(Environment*, ExitCode)>&& handler);
 
@@ -1144,6 +1147,7 @@ class Environment : public MemoryRetainer {
   std::unique_ptr<Realm> principal_realm_ = nullptr;
 
   builtins::BuiltinLoader builtin_loader_;
+  StartExecutionCallback embedder_mksnapshot_entry_point_;
 
   // Used by allocate_managed_buffer() and release_managed_buffer() to keep
   // track of the BackingStore for a given pointer.

src/node.cc

@@ -276,14 +276,21 @@ MaybeLocal<Value> StartExecution(Environment* env, StartExecutionCallback cb) {
   if (cb != nullptr) {
     EscapableHandleScope scope(env->isolate());
 
-    if (StartExecution(env, "internal/main/environment").IsEmpty()) return {};
+    if (env->isolate_data()->options()->build_snapshot) {
+      // TODO(addaleax): pass the callback to the main script more directly,
+      // e.g. by making StartExecution(env, builtin) parametrizable
+      env->set_embedder_mksnapshot_entry_point(std::move(cb));
+      auto reset_entry_point =
+          OnScopeLeave([&]() { env->set_embedder_mksnapshot_entry_point({}); });
+
+      return StartExecution(env, "internal/main/mksnapshot");
+    }
 
-    StartExecutionCallbackInfo info = {
+    if (StartExecution(env, "internal/main/environment").IsEmpty()) return {};
+    return scope.EscapeMaybe(cb({
         env->process_object(),
         env->builtin_module_require(),
-    };
-
-    return scope.EscapeMaybe(cb(info));
+    }));
   }
 
   // TODO(joyeecheung): move these conditions into JS land and let the