MaxListenersExceededWarning: Possible EventEmitter memory leak dete

Question

I've read about this error and know what it is, and also know how I can disable it by setting the MaxListeners to 0. But I'd like to know what is causing this error so I can handle it properly.

Basically here is a robot to check and see if my accounts have new messages or not. I need to check lots of accounts at once so I wrote this robot to do that. I have 4 functions in this code:

1 - load_proxy -> reads list of proxies from a file and puts them into an array
2 - load_accounts -> reads list of accounts from a file and puts them into an array
3 - init-> opens a browser , in a while loop fetching accounts and calling the next function  
4 - open_tab-> opens a tab in the browser and checks the account and calles the next function to log the result 

5 - wite_to_file-> writing the result into a text file 


const puppeteer = require('puppeteer');
const fs = require('fs');
const PROXYSTACK = [] ;
const PROXYDB = [] ;
const ACCOUNTSTACK = [] ;
const ACCOUNTDB = [] ;
var   inprogress = false ;


setInterval(()=>load_proxy() , 5000 );
setInterval(()=>load_accounts() , 5000 );
setInterval(function(){

    if( !inprogress)
    {
        init();
    }

} , 2000 );


function load_proxy(){

    var lines = fs.readFileSync('./proxy.txt', 'utf-8')
        .split('\n');

        for(var i = 0 ; i< lines.length ; i++ )
        {
            let line  = lines[i];
            if(line == '' || typeof line == 'undefined')
            {
                continue ;
            }

            line = line.replace('\r' , '');
            if(PROXYDB.includes(line))
                continue ;

            PROXYSTACK.push(line);
            PROXYDB.push(line);

        }

}
function load_accounts(){

    var lines = fs.readFileSync('./accounts.txt', 'utf-8')
        .split('\n');

        for(var i = 0 ; i< lines.length ; i++ )
        {
            let line  = lines[i];
            if(line == '' || typeof line == 'undefined')
            {
                continue ;
            }

            line = line.replace('\r' , '');
            if(ACCOUNTDB.includes(line))
                continue ;

            ACCOUNTDB.push(line);
            ACCOUNTSTACK.push(line);

        }

}



async function init(){

    inprogress = true ;

    if(PROXYSTACK.length <= 0 )
    {
        console.log('========================================= > OUT OF PROXY !!!!');
        inprogress = false ;
        return ;
    }

    if(ACCOUNTSTACK.length <= 0 )
    {
        console.log('========================================= > OUT OF ACCOUNT !!!!');
        inprogress = false ;
        return ;
    }

    var ipport =  PROXYSTACK.pop().replace('\r' , '');
    console.log(` ----> current ${ipport} `);

    var  browser = await puppeteer.launch({headless: true        ,  args: ['--proxy-server=' + ipport  , '--no-sandbox', '--disable-setuid-sandbox' , ]});
    browser._process.once('close', () => {
        console.log(' ------------------------  closed !');
        inprogress = false;
    });
    browser.on('disconnected', () => {
        console.log(' ------------------------  disconnecte !');
        inprogress = false;
    });

    var  mainpage = await browser.newPage();
    await mainpage.setViewport({width: 1200, height: 1000});

    while( inprogress )
    {
        var line_number = ACCOUNTSTACK.length ;
        if(line_number == 0 )
        {
            inprogress = false ;
            break ;
        }
        var account = ACCOUNTSTACK.pop();
        console.log(account);


        var check = await open_tab(account , line_number , mainpage);
        if(check === 'fatalerror')
        {
            console.log('========================================= >  FATAL ERROR CHANGING IP ');
            try {
                await browser.close();
            }
            catch (e) {

            }

            inprogress = false ;
        }


    }


}


async function open_tab(account  , line_num , mainpage ) {

    console.log(`  ---- > checking  ${account} `);
    let link = `https://example.com`;



    try {


        let user_password = account.split(':');


        if(!await mainpage.$('#username'))
        {
            console.log('...loading login page');
            await mainpage.goto(link , {timeout: 0});
            console.log('...done');

            if(await mainpage.$('.fatalerror'))
            {
                ACCOUNTSTACK.push(account);
                await mainpage.screenshot({path:  './fatalerror-a-'+line_num+'.jpg'  });
                return 'fatalerror';
            }

            console.log('...waitnign for login filds');

            await Promise.race([
                mainpage.waitForSelector('#username'),
                mainpage.waitForSelector('.fatalerror'),
            ]).catch(function (error) {
                throw new Error(error);
            });
            if(await mainpage.$('.fatalerror'))
            {
                ACCOUNTSTACK.push(account);
                await mainpage.screenshot({path:  './fatalerror-b-'+line_num+'.jpg'  });
                return 'fatalerror';
            }
            console.log('...done');



        }


        console.log('...typing user password');

        await mainpage.$eval('#username', (el ) => el.value = '' );
        await mainpage.$eval('#password', (el ) => el.value = '' );

        await mainpage.type('#username', user_password[0], {delay: 10})
        await mainpage.type('#password', user_password[1], {delay: 10})
        console.log('...done');

        console.log('...clicking login button');
        await mainpage.click('button.primary-button')

        await Promise.race([
            mainpage.waitForSelector('.theme-noticeerror-font'), // timeout
            mainpage.waitForSelector('.empty-inbox'), 
            mainpage.waitForSelector('.new-message'), 
            mainpage.waitForNavigation(),
        ]).catch(function (error) {
            throw new Error(error);
        });
        console.log('...done');

        if (await mainpage.$('.theme-noticeerror-font'))
        {
            console.log(account + '-- '+ line_num +' --> TIMEOUT')
            ACCOUNTSTACK.push(account);
            await mainpage.screenshot({path:  './timeout'+line_num+'.jpg'  });
            return 'fatalerror';

        }
        else if (await mainpage.$('.empty-inbox'))
        {
            console.log(account + '-- '+ line_num +' --> empty');
            wite_to_file('empty.txt' , account );

        }
        else if (await mainpage.$('.new-message'))
        {
            console.log(account + '-- '+ line_num +' --> new message')
            wite_to_file('newmsg.txt' , account );

        }



    }
    catch(e)
    {
        console.log(`--------ERRRO----${account}-${line_num}---------------------`);
        await mainpage.screenshot({path:  './images/error'+line_num+'.jpg'  });
        ACCOUNTSTACK.push(account);
        const html =  await mainpage.content();
        fs.writeFileSync('./images/error'+line_num+'.html', html);

    }
}


function wite_to_file( file , acc){

    fs.appendFile('./' + file ,   `${acc}\n` , function (err) {})

}

From time to time I get this error between my console.logs:

(node:17535) MaxListenersExceededWarning: Possible EventEmitter memory leak dete       cted. 11 lifecycleevent listeners added to [FrameManager]. Use emitter.setMaxLis    teners() to increase limit
(node:17535) MaxListenersExceededWarning: Possible EventEmitter memory leak dete       cted. 11 framenavigatedwithindocument listeners added to [FrameManager]. Use emi    tter.setMaxListeners() to increase limit

I'm not sure what is causing this or whether it's serious or not?

After running the code with --trace-warnings

(node:992) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 framedetached listeners added to [FrameManager]. Use emitter.setMaxListeners() to increase limit
    at _addListener (events.js:261:17)
    at FrameManager.addListener (events.js:277:10)
    at Function.addEventListener (/home/robot/node_modules/puppeteer/lib/helper.js:188:13)
    at new NavigatorWatcher (/home/robot/node_modules/puppeteer/lib/NavigatorWatcher.js:50:14)
    at Page.waitForNavigation (/home/robot/node_modules/puppeteer/lib/Page.js:618:21)
    at open_tab (/home/robot/psn.js:212:22)
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
    at async init (/home/robot/psn.js:115:21)
(node:992) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 response listeners added to [NetworkManager]. Use emitter.setMaxListeners() to increase limit
    at _addListener (events.js:261:17)
    at NetworkManager.addListener (events.js:277:10)
    at Function.addEventListener (/home/robot/node_modules/puppeteer/lib/helper.js:188:13)
    at Page.waitForNavigation (/home/robot/node_modules/puppeteer/lib/Page.js:621:29)
    at open_tab (/home/robot/psn.js:212:22)
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
    at async init (/home/robot/psn.js:115:21)

Answer 1

This generally happens when too many ansync functions have been called without finishing. And given that all async functions have a min timeout(0ms), they always get pushed to the end of the stack, and none of them will finish before a loop calling many of them.

Anyways, if you're trying to have tons of asynchronous events happen in parallel,

disable it by setting the MaxListeners to 0

process.setMaxListeners(0);

Alternatively, you can use for loops (not forEach), wrapped in an async function with awaits to make your code purely synchronous. This can make logging nicer, if run time is no object.

// example of de-parallelizing
(async () => {
  const userIds = await myDb.getAllUserIds();
  const usersWithoutFirstnames = [];

  for (userId of userIds) {
    console.log("Getting first name of user:", userId);
    const firstName = await myDb.getFirstName(userId);

    if (firstName) {
      console.log("SUCCESS: ", firstName);
    } else {
      console.log("First name not found");
      usersWithoutFirstnames.push(userId);
    }
  }
})(); // closures are back