cluster: respect listen backlog set by workers

PR-URL: #41623
Co-authored-by: Ouyang Yadong <oyydoibh@gmail.com>
Reviewed-By: Ouyang Yadong <oyydoibh@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Author: 2 people

doc/api/net.md

@@ -464,6 +464,10 @@ server.listen({
 });
 ```
 
+When `exclusive` is `true` and the underlying handle is shared, it is
+possible that several workers query a handle with different backlogs.
+In this case, the first `backlog` passed to the master process will be used.
+
 Starting an IPC server as root may cause the server path to be inaccessible for
 unprivileged users. Using `readableAll` and `writableAll` will make the server
 accessible for all users.

lib/internal/cluster/round_robin_handle.js

@@ -15,7 +15,7 @@ const { constants } = internalBinding('tcp_wrap');
 
 module.exports=RoundRobinHandle;
 
-functionRoundRobinHandle(key,address,{ port, fd, flags }){
+functionRoundRobinHandle(key,address,{ port, fd, flags, backlog}){
 this.key=key;
 this.all=newSafeMap();
 this.free=newSafeMap();
@@ -24,16 +24,17 @@ function RoundRobinHandle(key, address, { port, fd, flags }) {
 this.server=net.createServer(assert.fail);
 
 if(fd>=0)
-this.server.listen({ fd });
+this.server.listen({ fd, backlog});
 elseif(port>=0){
 this.server.listen({
  port,
 host: address,
 // Currently, net module only supports `ipv6Only` option in `flags`.
 ipv6Only: Boolean(flags&constants.UV_TCP_IPV6ONLY),
+ backlog,
 });
 }else
-this.server.listen(address);// UNIX socket path.
+this.server.listen(address,backlog);// UNIX socket path.
 
 this.server.once('listening',()=>{
 this.handle=this.server._handle;

lib/net.js

@@ -1386,6 +1386,7 @@ function listenInCluster(server, address, port, addressType,
 addressType: addressType,
 fd: fd,
  flags,
+ backlog,
 };
 
 // Get the primary's server handle, and listen on it

test/parallel/test-cluster-net-listen-backlog.js

@@ -0,0 +1,45 @@
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+// Monkey-patch `net.Server.listen`
+constnet=require('net');
+constcluster=require('cluster');
+
+// Force round-robin scheduling policy
+// as Windows defaults to SCHED_NONE
+// https://nodejs.org/docs/latest/api/cluster.html#clusterschedulingpolicy
+cluster.schedulingPolicy=cluster.SCHED_RR;
+
+// Ensures that the `backlog` is used to create a `net.Server`.
+constkExpectedBacklog=127;
+if(cluster.isMaster){
+constlisten=net.Server.prototype.listen;
+
+net.Server.prototype.listen=common.mustCall(
+function(...args){
+constoptions=args[0];
+if(typeofoptions==='object'){
+assert(options.backlog,kExpectedBacklog);
+}else{
+assert(args[1],kExpectedBacklog);
+}
+returnlisten.call(this, ...args);
+}
+);
+
+constworker=cluster.fork();
+worker.on('message',()=>{
+worker.disconnect();
+});
+}else{
+constserver=net.createServer();
+
+server.listen({
+host: common.localhostIPv4,
+port: 0,
+backlog: kExpectedBacklog,
+},common.mustCall(()=>{
+process.send(true);
+}));
+}