stream: pre-allocate _events

PR-URL: https://github.com/nodejs/node/pull/50428
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Vinícius Lourenço Claro Cardoso <contact@viniciusl.com.br>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/events.js

@@ -87,6 +87,7 @@ const {
 
 const kCapture = Symbol('kCapture');
 const kErrorMonitor = Symbol('events.errorMonitor');
+const kShapeMode = Symbol('shapeMode');
 const kMaxEventTargetListeners = Symbol('events.maxEventTargetListeners');
 const kMaxEventTargetListenersWarned =
   Symbol('events.maxEventTargetListenersWarned');
@@ -344,6 +345,9 @@ EventEmitter.init = function(opts) {
       this._events === ObjectGetPrototypeOf(this)._events) {
     this._events = { __proto__: null };
     this._eventsCount = 0;
+    this[kShapeMode] = false;
+  } else {
+    this[kShapeMode] = true;
   }
 
   this._maxListeners = this._maxListeners || undefined;
@@ -686,9 +690,13 @@ EventEmitter.prototype.removeListener =
         return this;
 
       if (list === listener || list.listener === listener) {
-        if (--this._eventsCount === 0)
+        this._eventsCount -= 1;
+
+        if (this[kShapeMode]) {
+          events[type] = undefined;
+        } else if (this._eventsCount === 0) {
           this._events = { __proto__: null };
-        else {
+        } else {
           delete events[type];
           if (events.removeListener)
             this.emit('removeListener', type, list.listener || listener);
@@ -750,6 +758,7 @@ EventEmitter.prototype.removeAllListeners =
           else
             delete events[type];
         }
+        this[kShapeMode] = false;
         return this;
       }
 
@@ -762,6 +771,7 @@ EventEmitter.prototype.removeAllListeners =
         this.removeAllListeners('removeListener');
         this._events = { __proto__: null };
         this._eventsCount = 0;
+        this[kShapeMode] = false;
         return this;
       }
 

lib/internal/streams/duplex.js

@@ -63,6 +63,24 @@ function Duplex(options) {
   if (!(this instanceof Duplex))
     return new Duplex(options);
 
+  this._events ??= {
+    close: undefined,
+    error: undefined,
+    prefinish: undefined,
+    finish: undefined,
+    drain: undefined,
+    data: undefined,
+    end: undefined,
+    readable: undefined,
+    // Skip uncommon events...
+    // pause: undefined,
+    // resume: undefined,
+    // pipe: undefined,
+    // unpipe: undefined,
+    // [destroyImpl.kConstruct]: undefined,
+    // [destroyImpl.kDestroy]: undefined,
+  };
+
   this._readableState = new Readable.ReadableState(options, this, true);
   this._writableState = new Writable.WritableState(options, this, true);
 

lib/internal/streams/readable.js

@@ -319,6 +319,21 @@ function Readable(options) {
   if (!(this instanceof Readable))
     return new Readable(options);
 
+  this._events ??= {
+    close: undefined,
+    error: undefined,
+    data: undefined,
+    end: undefined,
+    readable: undefined,
+    // Skip uncommon events...
+    // pause: undefined,
+    // resume: undefined,
+    // pipe: undefined,
+    // unpipe: undefined,
+    // [destroyImpl.kConstruct]: undefined,
+    // [destroyImpl.kDestroy]: undefined,
+  };
+
   this._readableState = new ReadableState(options, this, false);
 
   if (options) {

lib/internal/streams/writable.js

@@ -385,6 +385,17 @@ function Writable(options) {
   if (!(this instanceof Writable))
     return new Writable(options);
 
+  this._events ??= {
+    close: undefined,
+    error: undefined,
+    prefinish: undefined,
+    finish: undefined,
+    drain: undefined,
+    // Skip uncommon events...
+    // [destroyImpl.kConstruct]: undefined,
+    // [destroyImpl.kDestroy]: undefined,
+  };
+
   this._writableState = new WritableState(options, this, false);
 
   if (options) {

test/parallel/test-readline-interface.js

@@ -44,7 +44,7 @@ class FakeInput extends EventEmitter {
 function isWarned(emitter) {
   for (const name in emitter) {
     const listeners = emitter[name];
-    if (listeners.warned) return true;
+    if (listeners && listeners.warned) return true;
   }
   return false;
 }

test/parallel/test-readline-promises-interface.js

@@ -22,7 +22,7 @@ class FakeInput extends EventEmitter {
 function isWarned(emitter) {
   for (const name in emitter) {
     const listeners = emitter[name];
-    if (listeners.warned) return true;
+    if (listeners && listeners.warned) return true;
   }
   return false;
 }