fix: memoize channel(name) to make Channel identity stable per name

patch-garbage-collection-bug.js

@@ -1,5 +1,16 @@
 // There's a bug where a newly created channel is immediately garbage collected
 // @see https://github.com/nodejs/node/pull/47520
+//
+// The phony subscriber below keeps a created channel alive, but Node's channel(name)
+// can still return a brand-new Channel object for the same name on a subsequent call
+// (observed on Node 18 under certain workloads). A WeakSet keyed by Channel-object
+// identity can't merge those — each new object is treated as new and gets its own
+// phony subscriber. Callers that captured the earlier Channel in a closure end up
+// publishing to a different object than later subscribe()-ers attach to.
+//
+// To make channel identity stable per name (the contract callers expect), memoize
+// dc.channel(name) by name and short-circuit before delegating to the underlying
+// channel() on subsequent calls.
 const PHONY_SUBSCRIBE = function AVOID_GARBAGE_COLLECTION() {};
 
 const {
@@ -10,11 +21,15 @@ const {
 module.exports = function(unpatched) {
   const dc_channel = unpatched.channel;
   const channels = new WeakSet();
+  const byName = new Map();
 
   const dc = { ...unpatched };
 
   dc.channel = function() {
+    const name = arguments[0];
+    if (byName.has(name)) return byName.get(name);
     const ch = dc_channel.apply(this, arguments);
+    byName.set(name, ch);
 
     if (channels.has(ch)) return ch;
 

test/garbage-collection-patch.spec.js

@@ -0,0 +1,83 @@
+const test = require('tape');
+const patch = require('../patch-garbage-collection-bug.js');
+
+// Simulate the Node 18 bug: the underlying channel(name) returns a
+// brand-new Channel object on every call for the same name, even when
+// the previous one is still held alive by JS code. The patch's job is
+// to make dc.channel(name) return a stable Channel identity per name
+// regardless of what the underlying registry returns.
+function mockUnpatched() {
+  const calls = { count: 0 };
+  function channel(name) {
+    calls.count++;
+    return {
+      _subscribers: [],
+      _stores: new Map(),
+      _name: name,
+      _instanceId: calls.count,
+      subscribe(fn) { this._subscribers.push(fn); },
+      unsubscribe(fn) {
+        const i = this._subscribers.indexOf(fn);
+        if (i >= 0) this._subscribers.splice(i, 1);
+        return i >= 0;
+      },
+      publish(data) {
+        for (const sub of this._subscribers) sub(data);
+      }
+    };
+  }
+  return { channel, calls };
+}
+
+test('garbage-collection patch: dc.channel(name) returns stable identity across calls', t => {
+  const { channel, calls } = mockUnpatched();
+  const dc = patch({ channel });
+
+  const a = dc.channel('foo');
+  const b = dc.channel('foo');
+  const c = dc.channel('foo');
+
+  t.strictEqual(a, b, 'second call to dc.channel(name) returns same Channel object');
+  t.strictEqual(b, c, 'third call returns same Channel object');
+  t.ok(calls.count >= 1, 'underlying channel() was called at least once for first lookup');
+
+  const callsAfterMemoization = calls.count;
+  dc.channel('foo');
+  dc.channel('foo');
+  t.equal(calls.count, callsAfterMemoization,
+    'memoized lookups do not re-invoke the underlying channel()');
+
+  t.end();
+});
+
+test('garbage-collection patch: distinct names get distinct Channel objects', t => {
+  const { channel } = mockUnpatched();
+  const dc = patch({ channel });
+
+  const foo = dc.channel('foo');
+  const bar = dc.channel('bar');
+
+  t.notStrictEqual(foo, bar, 'different names return different Channel objects');
+  t.strictEqual(dc.channel('foo'), foo, 'foo memoization holds');
+  t.strictEqual(dc.channel('bar'), bar, 'bar memoization holds');
+  t.end();
+});
+
+test('garbage-collection patch: subscribers attach to the memoized Channel and receive publishes', t => {
+  // This is the end-to-end shape the bug produces: the publisher captures
+  // a Channel from one call, the subscriber attaches via a later call.
+  // Without memoization (when the underlying channel() misbehaves) the
+  // two see different Channel objects and the subscriber never fires.
+  const { channel } = mockUnpatched();
+  const dc = patch({ channel });
+
+  const publisher = dc.channel('observable');
+
+  let received = null;
+  dc.channel('observable').subscribe((data) => { received = data; });
+
+  publisher.publish('hello');
+
+  t.equal(received, 'hello', 'subscriber attached to a later dc.channel(name) lookup receives publishes from the earlier-captured Channel');
+  t.end();
+});