process: add 'worker' event

Provides a new `process.on('worker', (worker) =>{})` event that is triggered by the creation of a new `worker_thread.Worker`. The use case is to allow hooks to be installed for monitoring workers without having to modify the call sites around those. Signed-off-by: James M Snell <[email protected]> PR-URL: #38659 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Rich Trott <[email protected]> Reviewed-By: Gerhard Stöbich <[email protected]>

Author: jasnell

doc/api/process.md

@@ -457,6 +457,15 @@ of the custom deprecation.
 The `*-deprecation` command-line flags only affect warnings that use the name
 `'DeprecationWarning'`.
 
+### Event: `'worker'`
+<!-- YAML
+added: REPLACEME
+-->
+
+*`worker`{Worker} The{Worker} that was created.
+
+The `'worker'` event is emitted after a new{Worker} thread has been created.
+
 #### Emitting custom warnings
 
 See the [`process.emitWarning()`][process_emit_warning] method for issuing

lib/internal/worker.js

@@ -266,6 +266,8 @@ class Worker extends EventEmitter{
 };
 // Actually start the new thread now that everything is in place.
 this[kHandle].startThread();
+
+process.nextTick(()=>process.emit('worker',this));
 }
 
 [kOnExit](code,customErr,customErrReason){

test/parallel/test-worker-event.js

@@ -0,0 +1,13 @@
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{
+ Worker,
+}=require('worker_threads');
+
+process.on('worker',common.mustCall(({ threadId })=>{
+assert.strictEqual(threadId,1);
+}));
+
+newWorker('',{eval: true});