src: prepare platform for upstream V8 changes

V8 platform tasks may schedule other tasks (both background and
foreground), and may perform asynchronous operations like
resolving Promises.

To address that:

- Run the task queue drain call inside a callback scope.
  This makes sure asynchronous operations inside it, like
  resolving promises, lead to the microtask queue and any
  subsequent operations not being silently forgotten.
- Move the task queue drain call before `EmitBeforeExit()`
  and only run `EmitBeforeExit()` if there is no new event
  loop work.
- Account for possible new foreground tasks scheduled by
  background tasks in `DrainBackgroundTasks()`.

PR-URL: https://github.com/nodejs/node/pull/15428
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Matthew Loring <mattloring@google.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/src/node_internals.h b/src/node_internals.h
index 9371d442ad..fd8cc26a28 100644
--- a/src/node_internals.h
+++ b/src/node_internals.h
@@ -294,8 +294,36 @@ v8::MaybeLocal<v8::Value> InternalMakeCallback(
     v8::Local<v8::Value> argv[],
     async_context asyncContext);
 
+class InternalCallbackScope {
+ public:
+  // Tell the constructor whether its `object` parameter may be empty or not.
+  enum ResourceExpectation { kRequireResource, kAllowEmptyResource };
+  InternalCallbackScope(Environment* env,
+                        v8::Local<v8::Object> object,
+                        const async_context& asyncContext,
+                        ResourceExpectation expect = kRequireResource);
+  ~InternalCallbackScope();
+  void Close();
+
+  inline bool Failed() const { return failed_; }
+  inline void MarkAsFailed() { failed_ = true; }
+  inline bool IsInnerMakeCallback() const {
+    return callback_scope_.in_makecallback();
+  }
+
+ private:
+  Environment* env_;
+  async_context async_context_;
+  v8::Local<v8::Object> object_;
+  Environment::AsyncCallbackScope callback_scope_;
+  bool failed_ = false;
+  bool pushed_ids_ = false;
+  bool closed_ = false;
+};
+
 }  // namespace node
 
+
 #endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
 #endif  // SRC_NODE_INTERNALS_H_