MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 message lis teners added. Use emitter.setMaxListeners() to increase limit

Question

I know this might flag as a duplicate solution but the solution on stack overflow is not working for me.

Problem

(node:5716) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 message lis teners added. Use emitter.setMaxListeners() to increase limit. 

My codebase is huge and I facing this error sometimes I don't know why it is happening. I tried to increase the listeners limit but unfortunately, it is not working.

const EventEmitter = require('events'); const emitter = new EventEmitter() emitter.setMaxListeners(50) 

UPDATE

After Some browsing, I run this command to trace warning

node --trace-warnings index.babel.js 

Turns out be my socket.io code is the problem I am using socket.io with Redis. This is the error

node:14212) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 message li steners added. Use emitter.setMaxListeners() to increase limit     at _addListener (events.js:281:19)     at RedisClient.addListener (events.js:298:10)     at Namespace.<anonymous> (D:/newProject/services/socket.js:21:17)     at emitOne (events.js:115:13)     at Namespace.emit (events.js:210:7)     at Namespace.emit (D:\newProject\node_modules\socket.io\lib\namespace.js:213:10)     at D:\newProject\node_modules\socket.io\lib\namespace.js:181:14     at _combinedTickCallback (internal/process/next_tick.js:131:7)     at process._tickCallback (internal/process/next_tick.js:180:9) 

this is the code (But this code is for more specific tasks it will not execute all the time).

const redis = require('redis'); const config = require('../config'); const sub = redis.createClient(config.REDIS.port, config.REDIS.host); const pub = redis.createClient(config.REDIS.port, config.REDIS.host);  sub.subscribe('spread');  module.exports = io => {   io.on('connection', socket => {     /* To find the User Login  */     let passport = socket.handshake.session.passport;       if (typeof passport !== 'undefined') {       socket.on('typing:send', data => {         pub.publish('spread', JSON.stringify(data));       });        sub.on('message', (ch, msg) => {         // This is the Exact line where I am getting this error         io.emit(`${JSON.parse(msg).commonID}:receive`, { ...JSON.parse(msg) });       });     }   }); }; 

Answer 1

The default limit for Event Emitter is 10. You can increase it with the emitter.setMaxListeners. My suggestion is not to change it unless and until explicitly required, listeners are increased because you didn't unsubscribe. Now to your code.

const redis = require('redis'); const config = require('../config'); const sub = redis.createClient(config.REDIS.port, config.REDIS.host); const pub = redis.createClient(config.REDIS.port, config.REDIS.host);  sub.subscribe('spread');  module.exports = (io) => {   io.on('connection', (socket) => {     // this callback will be executed for all the socket connections.     let passport =       socket.handshake.session.passport; /* To find the User Login  */      if (typeof passport !== 'undefined') {       socket.on('typing:send', (data) => {         pub.publish('spread', JSON.stringify(data));       });        // this is where you are subscribing for each and every socket connected to your server       sub.on('message', (ch, msg) => {         // this is the Exact line where I am getting this error          // whereas you are emitting messages on socket manager, not on the socket.         io.emit(`${JSON.parse(msg).commonID}:receive`, { ...JSON.parse(msg) });       });     }   }); };

Now if we analyze the above code then if you open 20 socket connections to your server it will subscribe 20 times, here it is going wrong. Now if your requirement is to listen for the message published on Redis at the server level and then emit it on io then your code should be like below

const redis = require('redis'); const config = require('../config'); const sub = redis.createClient(config.REDIS.port, config.REDIS.host); const pub = redis.createClient(config.REDIS.port, config.REDIS.host);  sub.subscribe('spread');  module.exports = (io) => {   sub.on('message', (ch, msg) => {     // this is the Exact line where I am getting this error     io.emit(`${JSON.parse(msg).commonID}:receive`, { ...JSON.parse(msg) });   });    io.on('connection', (socket) => {     let passport =       socket.handshake.session.passport; /* To find the User Login  */      if (typeof passport !== 'undefined') {       socket.on('typing:send', (data) => {         pub.publish('spread', JSON.stringify(data));       });     }   }); };