lib: disable default memory leak warning for AbortSignal

This change sets the default `kMaxEventTargetListeners` property for `AbortSignal` instances to 0, disabling the check per default, to enable users to write isomorphic library code. If desirable, the max event target listeners check can still be enabled for individual `AbortSignal` instances by calling `setMaxListeners` on them. Refs: #54758 PR-URL: #55816 Reviewed-By: James M Snell <[email protected]> Reviewed-By: Antoine du Hamel <[email protected]>

Author: phryneas

doc/api/events.md

@@ -1171,6 +1171,10 @@ that a "possible EventEmitter memory leak" has been detected. For any single
 `EventEmitter`, the `emitter.getMaxListeners()` and `emitter.setMaxListeners()`
 methods can be used to temporarily avoid this warning:
 
+`defaultMaxListeners` has no effect on `AbortSignal` instances. While it is
+still possible to use [`emitter.setMaxListeners(n)`][] to set a warning limit
+for individual `AbortSignal` instances, per default `AbortSignal` instances will not warn.
+
 ```mjs
 import{EventEmitter } from'node:events';
 constemitter=newEventEmitter();

lib/internal/abort_controller.js

@@ -28,6 +28,7 @@ const{
  kResistStopPropagation,
  kWeakHandler,
 }=require('internal/event_target');
+const{ kMaxEventTargetListeners }=require('events');
 const{
  customInspectSymbol,
  kEmptyObject,
@@ -165,6 +166,7 @@ class AbortSignal extends EventTarget{
 }
 super();
 
+this[kMaxEventTargetListeners]=0;
 const{
  aborted =false,
  reason =undefined,

test/parallel/test-eventtarget-memoryleakwarning.js

@@ -12,22 +12,22 @@ const{setTimeout } = require('timers/promises');
 common.expectWarning({
 MaxListenersExceededWarning: [
 ['Possible EventTarget memory leak detected. 3 foo listeners added to '+
-'EventTarget. MaxListeners is 2. Use events.setMaxListeners() '+
+'EventTarget. MaxListeners is 2. Use events.setMaxListeners() '+
 'to increase limit'],
 ['Possible EventTarget memory leak detected. 3 foo listeners added to '+
-'[MessagePort [EventTarget]]. '+
-'MaxListeners is 2. '+
-'Use events.setMaxListeners() to increase '+
+'[MessagePort [EventTarget]]. '+
+'MaxListeners is 2. '+
+'Use events.setMaxListeners() to increase '+
 'limit'],
 ['Possible EventTarget memory leak detected. 3 foo listeners added to '+
-'[MessagePort [EventTarget]]. '+
-'MaxListeners is 2. '+
-'Use events.setMaxListeners() to increase '+
+'[MessagePort [EventTarget]]. '+
+'MaxListeners is 2. '+
+'Use events.setMaxListeners() to increase '+
 'limit'],
-['Possible EventTarget memory leak detected. 3 foo listeners added to '+
-'[AbortSignal]. '+
-'MaxListeners is 2. '+
-'Use events.setMaxListeners() to increase '+
+['Possible EventTarget memory leak detected. 2 foo listeners added to '+
+'[AbortSignal]. '+
+'MaxListeners is 1. '+
+'Use events.setMaxListeners() to increase '+
 'limit'],
 ],
 });
@@ -65,13 +65,25 @@ common.expectWarning({
 mc.port1.addEventListener('foo',()=>{});
 mc.port1.addEventListener('foo',()=>{});
 mc.port1.addEventListener('foo',()=>{});
+}
 
+{
+// No warning emitted because AbortController ignores `EventEmitter.defaultMaxListeners`
+setMaxListeners(2);
 constac=newAbortController();
 ac.signal.addEventListener('foo',()=>{});
 ac.signal.addEventListener('foo',()=>{});
 ac.signal.addEventListener('foo',()=>{});
 }
 
+{
+// Will still warn as `setMaxListeners` can still manually set a limit
+constac=newAbortController();
+setMaxListeners(1,ac.signal);
+ac.signal.addEventListener('foo',()=>{});
+ac.signal.addEventListener('foo',()=>{});
+}
+
 {
 // It works for EventEmitters also
 constee=newEventEmitter();