child_process: queue pending messages

It fixes the problem of the child process not receiving messages.
Fixes: #41134
PR-URL: #41221
Reviewed-By: Adrian Estrada <edsadr@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>

Author: ErickWendel

lib/internal/child_process.js

@@ -81,6 +81,7 @@ let HTTPParser;
 constMAX_HANDLE_RETRANSMISSIONS=3;
 constkChannelHandle=Symbol('kChannelHandle');
 constkIsUsedAsStdio=Symbol('kIsUsedAsStdio');
+constkPendingMessages=Symbol('kPendingMessages');
 
 // This object contain function to convert TCP objects to native handle objects
 // and back again.
@@ -526,6 +527,7 @@ class Control extends EventEmitter {
 constructor(channel){
 super();
 this.#channel =channel;
+this[kPendingMessages]=[];
 }
 
 // The methods keeping track of the counter are being used to track the
@@ -699,6 +701,24 @@ function setupChannel(target, channel, serializationMode) {
 });
 });
 
+target.on('newListener',function(){
+
+process.nextTick(()=>{
+if(!target.channel||!target.listenerCount('message'))
+return;
+
+constmessages=target.channel[kPendingMessages];
+const{ length }=messages;
+if(!length)return;
+
+for(leti=0;i<length;i++){
+ReflectApply(target.emit,target,messages[i]);
+}
+
+target.channel[kPendingMessages]=[];
+});
+});
+
 target.send=function(message,handle,options,callback){
 if(typeofhandle==='function'){
 callback=handle;
@@ -912,7 +932,15 @@ function setupChannel(target, channel, serializationMode) {
 };
 
 functionemit(event,message,handle){
-target.emit(event,message,handle);
+if('internalMessage'===event||target.listenerCount('message')){
+target.emit(event,message,handle);
+return;
+}
+
+ArrayPrototypePush(
+target.channel[kPendingMessages],
+[event,message,handle]
+);
 }
 
 functionhandleMessage(message,handle,internal){

test/es-module/test-esm-child-process-fork-main.mjs

@@ -0,0 +1,20 @@
+import'../common/index.mjs';
+importassertfrom'assert';
+import{fork}from'child_process';
+import{once}from'events';
+import{fileURLToPath}from'url';
+
+if(process.argv[2]!=='child'){
+constfilename=fileURLToPath(import.meta.url);
+constcp=fork(filename,['child']);
+constmessage='Hello World';
+cp.send(message);
+
+const[received]=awaitonce(cp,'message');
+assert.deepStrictEqual(received,message);
+
+cp.disconnect();
+awaitonce(cp,'exit');
+}else{
+process.on('message',(msg)=>process.send(msg));
+}