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Print error when EventEmitters get too many listeners

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This commit is contained in:
Ryan Dahl 2010-12-31 18:32:52 -08:00
parent e1f4b3f009
commit 9da75f39d9
2 changed files with 40 additions and 1 deletions
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8
doc/api/events.markdown
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@ -61,6 +61,14 @@ Remove a listener from the listener array for the specified event.
Removes all listeners from the listener array for the specified event. Removes all listeners from the listener array for the specified event.
#### emitter.setMaxListeners(n)
By default EventEmitters will print a warning if more than 10 listeners are
added to it. This is a useful default which helps finding memory leaks.
Obviously not all Emitters should be limited to 10. This function allows
that to be increased. Set to zero for unlimited.
#### emitter.listeners(event) #### emitter.listeners(event)
Returns an array of listeners for the specified event. This array can be Returns an array of listeners for the specified event. This array can be

33
lib/events.js
View File

@ -1,7 +1,18 @@
var EventEmitter = exports.EventEmitter = process.EventEmitter; var EventEmitter = exports.EventEmitter = process.EventEmitter;
var isArray = Array.isArray; var isArray = Array.isArray;
// By default EventEmitters will print a warning if more than
// 10 listeners are added to it. This is a useful default which
// helps finding memory leaks.
//
// Obviously not all Emitters should be limited to 10. This function allows
// that to be increased. Set to zero for unlimited.
var defaultMaxListeners = 10;
EventEmitter.prototype.setMaxListeners = function(n) {
this._events.maxListeners = n;
};
EventEmitter.prototype.emit = function(type) { EventEmitter.prototype.emit = function(type) {
// If there is no 'error' event listener then throw. // If there is no 'error' event listener then throw.
if (type === 'error') { if (type === 'error') {
@ -71,6 +82,26 @@ EventEmitter.prototype.addListener = function(type, listener) {
// Optimize the case of one listener. Don't need the extra array object. // Optimize the case of one listener. Don't need the extra array object.
this._events[type] = listener; this._events[type] = listener;
} else if (isArray(this._events[type])) { } else if (isArray(this._events[type])) {
// Check for listener leak
if (!this._events[type].warned) {
var m;
if (this._events.maxListeners !== undefined) {
m = this._events.maxListeners;
} else {
m = defaultMaxListeners;
}
if (m && m > 0 && this._events[type].length > m) {
this._events[type].warned = true;
console.error('(node) warning: possible EventEmitter memory ' +
'leak detected. %d listeners added. ' +
'Use emitter.setMaxListeners() to increase limit.',
this._events[type].length);
console.trace();
}
}
// If we've already got an array, just append. // If we've already got an array, just append.
this._events[type].push(listener); this._events[type].push(listener);
} else { } else {