worker: add hasRef() to the handle object

This should help projects like
https://github.com/mafintosh/why-is-node-running and
https://github.com/facebook/jest to detect if Worker instances are
keeping the event loop active correctly.

Fixes: https://github.com/nodejs/node/issues/42091
Refs: https://github.com/mafintosh/why-is-node-running/issues/59
Signed-off-by: Darshan Sen <raisinten@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/42756
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/test/parallel/test-worker-hasref.js b/test/parallel/test-worker-hasref.js
new file mode 100644
index 00000000000..51593b14725
--- /dev/null
+++ b/test/parallel/test-worker-hasref.js
@@ -0,0 +1,33 @@
+'use strict';
+const common = require('../common');
+
+const { Worker } = require('worker_threads');
+const { createHook } = require('async_hooks');
+const { strictEqual } = require('assert');
+
+let handle;
+
+createHook({
+  init(asyncId, type, triggerAsyncId, resource) {
+    if (type === 'WORKER') {
+      handle = resource;
+      this.disable();
+    }
+  }
+}).enable();
+
+const w = new Worker('', { eval: true });
+
+strictEqual(handle.hasRef(), true);
+w.unref();
+strictEqual(handle.hasRef(), false);
+w.ref();
+strictEqual(handle.hasRef(), true);
+
+w.on('exit', common.mustCall((exitCode) => {
+  strictEqual(exitCode, 0);
+  strictEqual(handle.hasRef(), true);
+  setTimeout(common.mustCall(() => {
+    strictEqual(handle.hasRef(), undefined);
+  }), 0);
+}));