n-api: napi_make_callback emit async init event with resource of async_context

doc/api/n-api.md

@@ -5189,19 +5189,31 @@ napi_status napi_async_init(napi_env env,
 
 * `[in] env`: The environment that the API is invoked under.
 * `[in] async_resource`: Object associated with the async work
-  that will be passed to possible `async_hooks` [`init` hooks][].
-  In order to retain ABI compatibility with previous versions,
-  passing `NULL` for `async_resource` does not result in an error. However,
-  this results in incorrect operation of async hooks for the
-  napi_async_context created. Potential issues include
-  loss of async context when using the AsyncLocalStorage API.
-* `[in] async_resource_name`: Identifier for the kind of resource
-  that is being provided for diagnostic information exposed by the
-  `async_hooks` API.
+  that will be passed to possible `async_hooks` [`init` hooks][] and can be
+  accessed by [`async_hooks.executionAsyncResource()`][].
+* `[in] async_resource_name`: Identifier for the kind of resource that is being
+  provided for diagnostic information exposed by the `async_hooks` API.
 * `[out] result`: The initialized async context.
 
 Returns `napi_ok` if the API succeeded.
 
+The `async_resource` object needs to be kept alive until
+[`napi_async_destroy`][] to keep `async_hooks` related API acts correctly. In
+order to retain ABI compatibility with previous versions, `napi_async_context`s
+are not maintaining the strong reference to the `async_resource` objects to
+avoid introducing causing memory leaks. However, if the `async_resource` is
+garbage collected by JavaScript engine before the `napi_async_context` was
+destroyed by `napi_async_destroy`, calling `napi_async_context` related APIs
+like [`napi_open_callback_scope`][] and [`napi_make_callback`][] can cause
+problems like loss of async context when using the `AsyncLocalStoage` API.
+
+In order to retain ABI compatibility with previous versions, passing `NULL`
+for `async_resource` does not result in an error. However, this is not
+recommended as this will result poor results with  `async_hooks`
+[`init` hooks][] and `async_hooks.executionAsyncResource()` as the resource is
+now required by the underlying `async_hooks` implementation in order to provide
+the linkage between async callbacks.
+
 ### napi_async_destroy
 <!-- YAML
 added: v8.6.0
@@ -5288,7 +5300,9 @@ NAPI_EXTERN napi_status napi_open_callback_scope(napi_env env,
 
 * `[in] env`: The environment that the API is invoked under.
 * `[in] resource_object`: An object associated with the async work
-  that will be passed to possible `async_hooks` [`init` hooks][].
+  that will be passed to possible `async_hooks` [`init` hooks][]. This
+  parameter has been deprecated and is ignored at runtime. Use the
+  `async_resource` parameter in [`napi_async_init`][] instead.
 * `[in] context`: Context for the async operation that is invoking the callback.
   This should be a value previously obtained from [`napi_async_init`][].
 * `[out] result`: The newly created scope.
@@ -5985,13 +5999,15 @@ This API may only be called from the main thread.
 [`Number.MAX_SAFE_INTEGER`]: https://tc39.github.io/ecma262/#sec-number.max_safe_integer
 [`Number.MIN_SAFE_INTEGER`]: https://tc39.github.io/ecma262/#sec-number.min_safe_integer
 [`Worker`]: worker_threads.md#worker_threads_class_worker
+[`async_hooks.executionAsyncResource()`]: async_hooks.md#async_hooks_async_hooks_executionasyncresource
 [`global`]: globals.md#globals_global
 [`init` hooks]: async_hooks.md#async_hooks_init_asyncid_type_triggerasyncid_resource
 [`napi_add_async_cleanup_hook`]: #n_api_napi_add_async_cleanup_hook
 [`napi_add_env_cleanup_hook`]: #n_api_napi_add_env_cleanup_hook
 [`napi_add_finalizer`]: #n_api_napi_add_finalizer
 [`napi_async_cleanup_hook`]: #n_api_napi_async_cleanup_hook
 [`napi_async_complete_callback`]: #n_api_napi_async_complete_callback
+[`napi_async_destroy`]: #n_api_napi_async_destroy
 [`napi_async_init`]: #n_api_napi_async_init
 [`napi_callback`]: #n_api_napi_callback
 [`napi_cancel_async_work`]: #n_api_napi_cancel_async_work

src/node_api.cc

@@ -1,12 +1,15 @@
+#include "async_wrap-inl.h"
 #include "env-inl.h"
 #define NAPI_EXPERIMENTAL
 #include "js_native_api_v8.h"
+#include "memory_tracker-inl.h"
 #include "node_api.h"
 #include "node_binding.h"
 #include "node_buffer.h"
 #include "node_errors.h"
 #include "node_internals.h"
 #include "threadpoolwork-inl.h"
+#include "tracing/traced_value.h"
 #include "util-inl.h"
 
 #include <memory>
@@ -104,16 +107,6 @@ static inline napi_env NewEnv(v8::Local<v8::Context> context) {
   return result;
 }
 
-static inline napi_callback_scope
-JsCallbackScopeFromV8CallbackScope(node::CallbackScope* s) {
-  return reinterpret_cast<napi_callback_scope>(s);
-}
-
-static inline node::CallbackScope*
-V8CallbackScopeFromJsCallbackScope(napi_callback_scope s) {
-  return reinterpret_cast<node::CallbackScope*>(s);
-}
-
 static inline void trigger_fatal_exception(
     napi_env env, v8::Local<v8::Value> local_err) {
   v8::Local<v8::Message> local_msg =
@@ -435,6 +428,111 @@ class ThreadSafeFunction : public node::AsyncResource {
   bool handles_closing;
 };
 
+/**
+ * Compared to node::AsyncResource, the resource object in AsyncContext is
+ * gc-able. AsyncContext holds a weak reference to the resource object.
+ * AsyncContext::MakeCallback doesn't implicitly set the receiver of the
+ * callback to the resource object.
+ */
+class AsyncContext {
+ public:
+  AsyncContext(node_napi_env env,
+               v8::Local<v8::Object> resource_object,
+               const v8::Local<v8::String> resource_name,
+               bool externally_managed_resource)
+      : env_(env) {
+    async_id_ = node_env()->new_async_id();
+    trigger_async_id_ = node_env()->get_default_trigger_async_id();
+    resource_.Reset(node_env()->isolate(), resource_object);
+    lost_reference_ = false;
+    if (externally_managed_resource) {
+      resource_.SetWeak(
+          this, AsyncContext::WeakCallback, v8::WeakCallbackType::kParameter);
+    }
+
+    node::AsyncWrap::EmitAsyncInit(node_env(),
+                                   resource_object,
+                                   resource_name,
+                                   async_id_,
+                                   trigger_async_id_);
+  }
+
+  ~AsyncContext() {
+    resource_.Reset();
+    lost_reference_ = true;
+    node::AsyncWrap::EmitDestroy(node_env(), async_id_);
+  }
+
+  inline v8::MaybeLocal<v8::Value> MakeCallback(
+      v8::Local<v8::Object> recv,
+      const v8::Local<v8::Function> callback,
+      int argc,
+      v8::Local<v8::Value> argv[]) {
+    EnsureReference();
+    return node::InternalMakeCallback(node_env(),
+                                      resource(),
+                                      recv,
+                                      callback,
+                                      argc,
+                                      argv,
+                                      {async_id_, trigger_async_id_});
+  }
+
+  inline napi_callback_scope OpenCallbackScope() {
+    EnsureReference();
+    napi_callback_scope it =
+        reinterpret_cast<napi_callback_scope>(new CallbackScope(this));
+    env_->open_callback_scopes++;
+    return it;
+  }
+
+  inline void EnsureReference() {
+    if (lost_reference_) {
+      const v8::HandleScope handle_scope(node_env()->isolate());
+      resource_.Reset(node_env()->isolate(),
+                      v8::Object::New(node_env()->isolate()));
+      lost_reference_ = false;
+    }
+  }
+
+  inline node::Environment* node_env() { return env_->node_env(); }
+  inline v8::Local<v8::Object> resource() {
+    return resource_.Get(node_env()->isolate());
+  }
+  inline node::async_context async_context() {
+    return {async_id_, trigger_async_id_};
+  }
+
+  static inline void CloseCallbackScope(node_napi_env env,
+                                        napi_callback_scope s) {
+    CallbackScope* callback_scope = reinterpret_cast<CallbackScope*>(s);
+    delete callback_scope;
+    env->open_callback_scopes--;
+  }
+
+  static void WeakCallback(const v8::WeakCallbackInfo<AsyncContext>& data) {
+    AsyncContext* async_context = data.GetParameter();
+    async_context->resource_.Reset();
+    async_context->lost_reference_ = true;
+  }
+
+ private:
+  class CallbackScope : public node::CallbackScope {
+   public:
+    explicit CallbackScope(AsyncContext* async_context)
+        : node::CallbackScope(async_context->node_env()->isolate(),
+                              async_context->resource_.Get(
+                                  async_context->node_env()->isolate()),
+                              async_context->async_context()) {}
+  };
+
+  node_napi_env env_;
+  double async_id_;
+  double trigger_async_id_;
+  v8::Global<v8::Object> resource_;
+  bool lost_reference_;
+};
+
 }  // end of anonymous namespace
 
 }  // end of namespace v8impl
@@ -627,28 +725,19 @@ NAPI_NO_RETURN void napi_fatal_error(const char* location,
 }
 
 napi_status napi_open_callback_scope(napi_env env,
-                                     napi_value resource_object,
+                                     napi_value /** ignored */,
                                      napi_async_context async_context_handle,
                                      napi_callback_scope* result) {
   // Omit NAPI_PREAMBLE and GET_RETURN_STATUS because V8 calls here cannot throw
   // JS exceptions.
   CHECK_ENV(env);
   CHECK_ARG(env, result);
 
-  v8::Local<v8::Context> context = env->context();
-
-  node::async_context* node_async_context =
-      reinterpret_cast<node::async_context*>(async_context_handle);
-
-  v8::Local<v8::Object> resource;
-  CHECK_TO_OBJECT(env, context, resource, resource_object);
+  v8impl::AsyncContext* node_async_context =
+      reinterpret_cast<v8impl::AsyncContext*>(async_context_handle);
 
-  *result = v8impl::JsCallbackScopeFromV8CallbackScope(
-      new node::CallbackScope(env->isolate,
-                              resource,
-                              *node_async_context));
+  *result = node_async_context->OpenCallbackScope();
 
-  env->open_callback_scopes++;
   return napi_clear_last_error(env);
 }
 
@@ -661,8 +750,9 @@ napi_status napi_close_callback_scope(napi_env env, napi_callback_scope scope) {
     return napi_callback_scope_mismatch;
   }
 
-  env->open_callback_scopes--;
-  delete v8impl::V8CallbackScopeFromJsCallbackScope(scope);
+  v8impl::AsyncContext::CloseCallbackScope(reinterpret_cast<node_napi_env>(env),
+                                           scope);
+
   return napi_clear_last_error(env);
 }
 
@@ -678,20 +768,24 @@ napi_status napi_async_init(napi_env env,
   v8::Local<v8::Context> context = env->context();
 
   v8::Local<v8::Object> v8_resource;
+  bool externally_managed_resource;
   if (async_resource != nullptr) {
     CHECK_TO_OBJECT(env, context, v8_resource, async_resource);
+    externally_managed_resource = true;
   } else {
     v8_resource = v8::Object::New(isolate);
+    externally_managed_resource = false;
   }
 
   v8::Local<v8::String> v8_resource_name;
   CHECK_TO_STRING(env, context, v8_resource_name, async_resource_name);
 
-  // TODO(jasongin): Consider avoiding allocation here by using
-  // a tagged pointer with 2×31 bit fields instead.
-  node::async_context* async_context = new node::async_context();
+  auto async_context =
+      new v8impl::AsyncContext(reinterpret_cast<node_napi_env>(env),
+                               v8_resource,
+                               v8_resource_name,
+                               externally_managed_resource);
 
-  *async_context = node::EmitAsyncInit(isolate, v8_resource, v8_resource_name);
   *result = reinterpret_cast<napi_async_context>(async_context);
 
   return napi_clear_last_error(env);
@@ -702,11 +796,8 @@ napi_status napi_async_destroy(napi_env env,
   CHECK_ENV(env);
   CHECK_ARG(env, async_context);
 
-  node::async_context* node_async_context =
-      reinterpret_cast<node::async_context*>(async_context);
-  node::EmitAsyncDestroy(
-      reinterpret_cast<node_napi_env>(env)->node_env(),
-      *node_async_context);
+  v8impl::AsyncContext* node_async_context =
+      reinterpret_cast<v8impl::AsyncContext*>(async_context);
 
   delete node_async_context;
 
@@ -734,17 +825,25 @@ napi_status napi_make_callback(napi_env env,
   v8::Local<v8::Function> v8func;
   CHECK_TO_FUNCTION(env, v8func, func);
 
-  node::async_context* node_async_context =
-    reinterpret_cast<node::async_context*>(async_context);
-  if (node_async_context == nullptr) {
-    static node::async_context empty_context = { 0, 0 };
-    node_async_context = &empty_context;
-  }
+  v8::MaybeLocal<v8::Value> callback_result;
 
-  v8::MaybeLocal<v8::Value> callback_result = node::MakeCallback(
-      env->isolate, v8recv, v8func, argc,
-      reinterpret_cast<v8::Local<v8::Value>*>(const_cast<napi_value*>(argv)),
-      *node_async_context);
+  if (async_context == nullptr) {
+    callback_result = node::MakeCallback(
+        env->isolate,
+        v8recv,
+        v8func,
+        argc,
+        reinterpret_cast<v8::Local<v8::Value>*>(const_cast<napi_value*>(argv)),
+        {0, 0});
+  } else {
+    auto node_async_context =
+        reinterpret_cast<v8impl::AsyncContext*>(async_context);
+    callback_result = node_async_context->MakeCallback(
+        v8recv,
+        v8func,
+        argc,
+        reinterpret_cast<v8::Local<v8::Value>*>(const_cast<napi_value*>(argv)));
+  }
 
   if (try_catch.HasCaught()) {
     return napi_set_last_error(env, napi_pending_exception);