worker: add ability to unshift message from MessagePort

In combination with Atomics, this makes it possible to implement
generic synchronous functionality, e.g. `importScript()`, in Workers
purely by communicating with other threads.

This is a continuation of https://github.com/nodejs/node/pull/26686,
where a preference for a solution was voiced that allowed reading
individual messages, rather than emitting all messages through events.

PR-URL: https://github.com/nodejs/node/pull/27294
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/node_messaging.h b/src/node_messaging.h
index 08a6798e3c..9f7929aa1c 100644
--- a/src/node_messaging.h
+++ b/src/node_messaging.h
@@ -163,6 +163,7 @@ class MessagePort : public HandleWrap {
   static void Start(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void Stop(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void Drain(const v8::FunctionCallbackInfo<v8::Value>& args);
+  static void ReceiveMessage(const v8::FunctionCallbackInfo<v8::Value>& args);
 
   /* static */
   static void MoveToContext(const v8::FunctionCallbackInfo<v8::Value>& args);
@@ -200,6 +201,8 @@ class MessagePort : public HandleWrap {
   void OnClose() override;
   void OnMessage();
   void TriggerAsync();
+  v8::MaybeLocal<v8::Value> ReceiveMessage(v8::Local<v8::Context> context,
+                                           bool only_if_receiving);
 
   std::unique_ptr<MessagePortData> data_ = nullptr;
   bool receiving_messages_ = false;