From 1d8a320a04d75b2143be0bc97b10dfcd9e64defa Mon Sep 17 00:00:00 2001
From: Darshan Sen <raisinten@gmail.com>
Date: Mon, 2 May 2022 10:09:39 +0530
Subject: [PATCH] worker: add hasRef() to MessagePort

Since we were removing the hasRef() method before exposing the
MessagePort object, the only way of knowing if the handle was keeping
the event loop active was to parse the string returned by
util.inspect(port), which is inconvenient and inconsistent with most of
the other async resources. So this change stops removing hasRef() from
the MessagePort prototype. The reason why this is also being documented
is that while reporting active resources, async_hooks returns the same
MessagePort object as the one that is accessible by users.

Refs: https://github.com/nodejs/node/issues/42091#issuecomment-1104793189
Signed-off-by: Darshan Sen <raisinten@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/42849
Reviewed-By: Anna Henningsen <anna@addaleax.net>
---
 doc/api/worker_threads.md                     | 12 ++++
 lib/internal/worker/io.js                     |  5 +-
 test/parallel/test-messageport-hasref.js      | 57 +++++++++++++++++++
 test/parallel/test-worker-message-port.js     |  4 +-
 .../test-worker-messageport-hasref.js         | 45 +++++++++++++++
 5 files changed, 120 insertions(+), 3 deletions(-)
 create mode 100644 test/parallel/test-messageport-hasref.js
 create mode 100644 test/parallel/test-worker-messageport-hasref.js

diff --git a/doc/api/worker_threads.md b/doc/api/worker_threads.md
index 00b790e6e88e53..dc37b6d18adeee 100644
--- a/doc/api/worker_threads.md
+++ b/doc/api/worker_threads.md
@@ -767,6 +767,18 @@ port2.postMessage(new URL('https://example.org'));
 // Prints: { }
 ```
 
+### `port.hasRef()`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+* Returns: {boolean}
+
+If true, the `MessagePort` object will keep the Node.js event loop active.
+
 ### `port.ref()`
 
 <!-- YAML
diff --git a/lib/internal/worker/io.js b/lib/internal/worker/io.js
index 822b8672525da3..996d98995108d0 100644
--- a/lib/internal/worker/io.js
+++ b/lib/internal/worker/io.js
@@ -91,7 +91,7 @@ const messageTypes = {
 // We have to mess with the MessagePort prototype a bit, so that a) we can make
 // it inherit from NodeEventTarget, even though it is a C++ class, and b) we do
 // not provide methods that are not present in the Browser and not documented
-// on our side (e.g. hasRef).
+// on our side (e.g. stopMessagePort).
 // Save a copy of the original set of methods as a shallow clone.
 const MessagePortPrototype = ObjectCreate(
   ObjectGetPrototypeOf(MessagePort.prototype),
@@ -103,6 +103,9 @@ ObjectSetPrototypeOf(MessagePort.prototype, NodeEventTarget.prototype);
 // changing the prototype of MessagePort.prototype implicitly removed them.
 MessagePort.prototype.ref = MessagePortPrototype.ref;
 MessagePort.prototype.unref = MessagePortPrototype.unref;
+MessagePort.prototype.hasRef = function() {
+  return !!FunctionPrototypeCall(MessagePortPrototype.hasRef, this);
+};
 
 function validateMessagePort(port, name) {
   if (!checkMessagePort(port))
diff --git a/test/parallel/test-messageport-hasref.js b/test/parallel/test-messageport-hasref.js
new file mode 100644
index 00000000000000..bc213f7897d277
--- /dev/null
+++ b/test/parallel/test-messageport-hasref.js
@@ -0,0 +1,57 @@
+'use strict';
+const common = require('../common');
+
+const { MessageChannel } = require('worker_threads');
+const { createHook } = require('async_hooks');
+const { strictEqual } = require('assert');
+
+const handles = [];
+
+createHook({
+  init(asyncId, type, triggerAsyncId, resource) {
+    if (type === 'MESSAGEPORT') {
+      handles.push(resource);
+    }
+  }
+}).enable();
+
+const { port1, port2 } = new MessageChannel();
+strictEqual(handles[0], port1);
+strictEqual(handles[1], port2);
+
+strictEqual(handles[0].hasRef(), false);
+strictEqual(handles[1].hasRef(), false);
+
+port1.unref();
+strictEqual(handles[0].hasRef(), false);
+
+port1.ref();
+strictEqual(handles[0].hasRef(), true);
+
+port1.unref();
+strictEqual(handles[0].hasRef(), false);
+
+port1.on('message', () => {});
+strictEqual(handles[0].hasRef(), true);
+
+port2.unref();
+strictEqual(handles[1].hasRef(), false);
+
+port2.ref();
+strictEqual(handles[1].hasRef(), true);
+
+port2.unref();
+strictEqual(handles[1].hasRef(), false);
+
+port2.on('message', () => {});
+strictEqual(handles[0].hasRef(), true);
+
+port1.on('close', common.mustCall(() => {
+  strictEqual(handles[0].hasRef(), false);
+  strictEqual(handles[1].hasRef(), false);
+}));
+
+port2.close();
+
+strictEqual(handles[0].hasRef(), true);
+strictEqual(handles[1].hasRef(), true);
diff --git a/test/parallel/test-worker-message-port.js b/test/parallel/test-worker-message-port.js
index ca28f6ccb73247..2663dde2a1b75f 100644
--- a/test/parallel/test-worker-message-port.js
+++ b/test/parallel/test-worker-message-port.js
@@ -179,7 +179,7 @@ const { MessageChannel, MessagePort } = require('worker_threads');
   assert.deepStrictEqual(
     Object.getOwnPropertyNames(MessagePort.prototype).sort(),
     [
-      'close', 'constructor', 'onmessage', 'onmessageerror', 'postMessage',
-      'ref', 'start', 'unref',
+      'close', 'constructor', 'hasRef', 'onmessage', 'onmessageerror',
+      'postMessage', 'ref', 'start', 'unref',
     ]);
 }
diff --git a/test/parallel/test-worker-messageport-hasref.js b/test/parallel/test-worker-messageport-hasref.js
new file mode 100644
index 00000000000000..448787742e308d
--- /dev/null
+++ b/test/parallel/test-worker-messageport-hasref.js
@@ -0,0 +1,45 @@
+'use strict';
+const common = require('../common');
+
+const { Worker } = require('worker_threads');
+const { createHook } = require('async_hooks');
+const { deepStrictEqual, strictEqual } = require('assert');
+
+const m = new Map();
+createHook({
+  init(asyncId, type, triggerAsyncId, resource) {
+    if (['WORKER', 'MESSAGEPORT'].includes(type)) {
+      m.set(asyncId, { type, resource });
+    }
+  },
+  destroy(asyncId) {
+    m.delete(asyncId);
+  }
+}).enable();
+
+function getActiveWorkerAndMessagePortTypes() {
+  const activeWorkerAndMessagePortTypes = [];
+  for (const asyncId of m.keys()) {
+    const { type, resource } = m.get(asyncId);
+    // Same logic as https://github.com/mafintosh/why-is-node-running/blob/24fb4c878753390a05d00959e6173d0d3c31fddd/index.js#L31-L32.
+    if (typeof resource.hasRef !== 'function' || resource.hasRef() === true) {
+      activeWorkerAndMessagePortTypes.push(type);
+    }
+  }
+  return activeWorkerAndMessagePortTypes;
+}
+
+const w = new Worker('', { eval: true });
+deepStrictEqual(getActiveWorkerAndMessagePortTypes(), ['WORKER']);
+w.unref();
+deepStrictEqual(getActiveWorkerAndMessagePortTypes(), []);
+w.ref();
+deepStrictEqual(getActiveWorkerAndMessagePortTypes(), ['WORKER', 'MESSAGEPORT']);
+
+w.on('exit', common.mustCall((exitCode) => {
+  strictEqual(exitCode, 0);
+  deepStrictEqual(getActiveWorkerAndMessagePortTypes(), ['WORKER']);
+  setTimeout(common.mustCall(() => {
+    deepStrictEqual(getActiveWorkerAndMessagePortTypes(), []);
+  }), 0);
+}));