src: add helper for before/after scope without JS calls

Add `AsyncScope` for cases where the async_hooks `before` and
`after` callbacks should be called, to track async context,
but no actual JS is called in between and we can therefore
skip things like draining the microtask or `nextTick` queues.

PR-URL: https://github.com/nodejs/node/pull/18936
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

src/async_wrap-inl.h

@@ -45,6 +45,22 @@ inline double AsyncWrap::get_trigger_async_id() const {
 }
 
 
+inline AsyncWrap::AsyncScope::AsyncScope(AsyncWrap* wrap)
+    : wrap_(wrap) {
+  Environment* env = wrap->env();
+  if (env->async_hooks()->fields()[Environment::AsyncHooks::kBefore] == 0)
+    return;
+  EmitBefore(env, wrap->get_async_id());
+}
+
+inline AsyncWrap::AsyncScope::~AsyncScope() {
+  Environment* env = wrap_->env();
+  if (env->async_hooks()->fields()[Environment::AsyncHooks::kAfter] == 0)
+    return;
+  EmitAfter(env, wrap_->get_async_id());
+}
+
+
 inline v8::MaybeLocal<v8::Value> AsyncWrap::MakeCallback(
     const v8::Local<v8::String> symbol,
     int argc,

src/async_wrap.h

@@ -169,6 +169,18 @@ class AsyncWrap : public BaseObject {
 
   static void WeakCallback(const v8::WeakCallbackInfo<DestroyParam> &info);
 
+  // This is a simplified version of InternalCallbackScope that only runs
+  // the `before` and `after` hooks. Only use it when not actually calling
+  // back into JS; otherwise, use InternalCallbackScope.
+  class AsyncScope {
+   public:
+    explicit inline AsyncScope(AsyncWrap* wrap);
+    ~AsyncScope();
+
+   private:
+    AsyncWrap* wrap_ = nullptr;
+  };
+
  private:
   friend class PromiseWrap;