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events: fix weak listener retention overwrite #64024

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events: fix weak listener retention overwrite #64024

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27 changes: 24 additions & 3 deletions lib/internal/event_target.js
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ const {
ReflectApply,
SafeFinalizationRegistry,
SafeMap,
SafeSet,
SafeWeakMap,
SafeWeakRef,
SafeWeakSet,
Expand Down Expand Up @@ -491,8 +492,17 @@ class Listener {
listener: this,
eventType,
}, this);
// Make the retainer retain the listener in a WeakMap
weakListeners().map.set(weak, listener);
// Store only a WeakRef to the retainer here. Listener instances are
// Strongly reachable from the EventTarget's listener list for as long
// as they're registered, so a plain strong reference would keep the
// retainer (and listener) alive forever, defeating weak retention
this.weakKeyRef = new SafeWeakRef(weak);
let retained = weakListeners().map.get(weak);
if (retained === undefined) {
retained = new SafeSet();
weakListeners().map.set(weak, retained);
}
retained.add(listener);
this.listener = this.callback;
} else if (typeof listener === 'function') {
this.callback = listener;
Expand Down Expand Up @@ -545,8 +555,19 @@ class Listener {
if (this.next !== undefined)
this.next.previous = this.previous;
this.removed = true;
if (this.weak)
if (this.weak) {
weakListeners().registry.unregister(this);
const weakKey = this.weakKeyRef?.deref();
const listener = this.callback?.deref();
if (weakKey !== undefined && listener !== undefined) {
const retained = weakListeners().map.get(weakKey);
if (retained !== undefined) {
retained.delete(listener);
if (retained.size === 0)
weakListeners().map.delete(weakKey);
}
}
}
}
}

Expand Down
19 changes: 19 additions & 0 deletions test/parallel/test-abortcontroller-internal.js
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Original file line number Diff line number Diff line change
Expand Up @@ -30,3 +30,22 @@ test('A weak event listener should not prevent gc', async () => {
globalThis.gc();
assert.strictEqual(ref.deref(), undefined);
});

test('two weak listeners with the same retainer should both run on abort', async () => {
// Regression test for https://github.com/nodejs/node/issues/63954
const ac = new AbortController();
let aRan = false;
let bRan = false;

ac.signal.addEventListener('a', () => { aRan = true; }, { [kWeakHandler]: ac });
ac.signal.addEventListener('b', () => { bRan = true; }, { [kWeakHandler]: ac });

await sleep(10);
globalThis.gc();

ac.signal.dispatchEvent(new Event('a'));
ac.signal.dispatchEvent(new Event('b'));

assert.strictEqual(aRan, true);
assert.strictEqual(bRan, true);
});
16 changes: 15 additions & 1 deletion test/parallel/test-eventtarget.js
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Original file line number Diff line number Diff line change
Expand Up @@ -685,7 +685,21 @@ let asyncTest = Promise.resolve();
et.dispatchEvent(new Event('foo'));
});
}

{
// Two listeners sharing the same retainer key must NOT evict each
// other from the weak retention map — both must survive a GC cycle
// and both must be removable independently.
// Regression test for https://github.com/nodejs/node/issues/63954
const et = new EventTarget();
const aCalled = common.mustNotCall();
const bCalled = common.mustCall();
et.addEventListener('a', aCalled, { [kWeakHandler]: et });
et.addEventListener('b', bCalled, { [kWeakHandler]: et });
globalThis.gc();
et.removeEventListener('a', aCalled);
et.dispatchEvent(new Event('a'));
et.dispatchEvent(new Event('b'));
}
{
const et = new EventTarget();

Expand Down
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