Give top-level an empty object as a resource

Author: Qard

doc/api/async_hooks.md

@@ -509,8 +509,6 @@ const server = createServer(function(req, res) {
 }).listen(3000);
 ```
 
-`executionAsyncResource()` will return `null` during application bootstrap.
-
 Resource objects returned by `executionAsyncResource()` are often internal
 handle objects with undocumented APIs. Using any functions or properties
 on the object is not recommended and may crash your application.

src/env.cc

@@ -382,6 +382,8 @@ Environment::Environment(IsolateData* isolate_data,
     async_hooks_.no_force_checks();
   }
 
+  async_hooks_.push_execution_async_resource(v8::Object::New(isolate_));
+
   // TODO(joyeecheung): deserialize when the snapshot covers the environment
   // properties.
   CreateProperties();
@@ -418,6 +420,8 @@ Environment::~Environment() {
   TRACE_EVENT_NESTABLE_ASYNC_END0(
     TRACING_CATEGORY_NODE1(environment), "Environment", this);
 
+  async_hooks_.pop_execution_async_resource();
+
   // Do not unload addons on the main thread. Some addons need to retain memory
   // beyond the Environment's lifetime, and unloading them early would break
   // them; with Worker threads, we have the opportunity to be stricter.

test/parallel/test-async-hooks-current-resource-await.js

@@ -11,6 +11,8 @@ const id = Symbol('id');
 // Tests continuation local storage with the currentResource API
 // through an async function
 
+assert.ok(executionAsyncResource());
+
 createHook({
   init(asyncId, type, triggerAsyncId, resource) {
     const cr = executionAsyncResource();

test/parallel/test-async-hooks-current-resource.js

@@ -9,6 +9,8 @@ const id = Symbol('id');
 
 // Tests continuation local storage with the executionAsyncResource API
 
+assert.ok(executionAsyncResource());
+
 createHook({
   init(asyncId, type, triggerAsyncId, resource) {
     const cr = executionAsyncResource();