From 99735a6fe8f1f19ee07cd9c6d2be76c0ffda7230 Mon Sep 17 00:00:00 2001
From: James M Snell <jasnell@gmail.com>
Date: Wed, 12 May 2021 15:10:32 -0700
Subject: [PATCH] process: add `'worker'` event
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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 <jasnell@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/38659
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
---
 doc/api/process.md                 |  9 +++++++++
 lib/internal/worker.js             |  2 ++
 test/parallel/test-worker-event.js | 13 +++++++++++++
 3 files changed, 24 insertions(+)
 create mode 100644 test/parallel/test-worker-event.js

diff --git a/doc/api/process.md b/doc/api/process.md
index eb1e388fc6eaea..c5ea3d7b9077af 100644
--- a/doc/api/process.md
+++ b/doc/api/process.md
@@ -455,6 +455,15 @@ 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
diff --git a/lib/internal/worker.js b/lib/internal/worker.js
index 2b35791473d1fa..2bf1d3de567b23 100644
--- a/lib/internal/worker.js
+++ b/lib/internal/worker.js
@@ -261,6 +261,8 @@ 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) {
diff --git a/test/parallel/test-worker-event.js b/test/parallel/test-worker-event.js
new file mode 100644
index 00000000000000..9d6056e1091468
--- /dev/null
+++ b/test/parallel/test-worker-event.js
@@ -0,0 +1,13 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const {
+  Worker,
+} = require('worker_threads');
+
+process.on('worker', common.mustCall(({ threadId }) => {
+  assert.strictEqual(threadId, 1);
+}));
+
+new Worker('', { eval: true });