net: create diagnostics channels lazily

PR-URL: #38905
Refs: #35711
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Author: joyeecheung

lib/net.js

@@ -135,9 +135,20 @@ const noop = () => {};
 
 const kPerfHooksNetConnectContext = Symbol('kPerfHooksNetConnectContext');
 
-const dc = require('diagnostics_channel');
-const netClientSocketChannel = dc.channel('net.client.socket');
-const netServerSocketChannel = dc.channel('net.server.socket');
+let netClientSocketChannel;
+let netServerSocketChannel;
+function lazyChannels() {
+  // TODO(joyeecheung): support diagnostics channels in the snapshot.
+  // For now it is fine to create them lazily when there isn't a snapshot to
+  // build. If users need the channels they would have to create them first
+  // before invoking any built-ins that would publish to these channels
+  // anyway.
+  if (netClientSocketChannel === undefined) {
+    const dc = require('diagnostics_channel');
+    netClientSocketChannel = dc.channel('net.client.socket');
+    netServerSocketChannel = dc.channel('net.server.socket');
+  }
+}
 
 const {
   hasObserver,
@@ -210,6 +221,7 @@ function connect(...args) {
   const options = normalized[0];
   debug('createConnection', normalized);
   const socket = new Socket(options);
+  lazyChannels();
   if (netClientSocketChannel.hasSubscribers) {
     netClientSocketChannel.publish({
       socket,
@@ -1756,6 +1768,7 @@ function onconnection(err, clientHandle) {
 
   DTRACE_NET_SERVER_CONNECTION(socket);
   self.emit('connection', socket);
+  lazyChannels();
   if (netServerSocketChannel.hasSubscribers) {
     netServerSocketChannel.publish({
       socket,

test/parallel/test-bootstrap-modules.js

@@ -171,7 +171,6 @@ const expectedModules = new Set([
   'NativeModule v8',
   'NativeModule internal/v8/startup_snapshot',
   'NativeModule vm',
-  'NativeModule diagnostics_channel',
 ]);
 
 if (!common.isMainThread) {