Piping a simple program to stdout gives "MaxListenersExceededWarning: Possible EventEmitter memory leak detected when"

[mafintosh]

• Version: v8.9.0
• Platform: Linux brunhilde 4.13.8-1-ARCH deps: update openssl to 1.0.1j #1 SMP PREEMPT Wed Oct 18 11:49:44 CEST 2017 x86_64 GNU/Linux
• Subsystem: console.js

When running a program that produces a lot of output that is consumed by another program in the pipeline, Node gives memory leak errors.

To reproduce try saving this simple program:

// save as bug.js
for (var i = 0; i < 10000; i++) {
  console.log('line ' + i)
}

Then run

node bug.js | less

And quit less (type q). This results in the following warning being printed out:

(node:31009) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 error listeners added. Use emitter.setMaxListeners() to increase limit

@mcollina mentioned it is most likely a bug here, https://github.com/nodejs/node/blob/master/lib/console.js#L91-L119

(In general it would be useful as well if the memory leak errors printed out a stack trace so it was easier to hunt down the causes)

/cc @mcollina @addaleax

[mscdex]

(In general it would be useful as well if the memory leak errors printed out a stack trace so it was easier to hunt down the causes)

You mean --trace-warnings ?

[addaleax]

Fwiw, I couldn’t reproduce this with master or with v8.9.0… but yes, --trace-warnings should give a good hint at what’s going on.

[mscdex]

I'm also not able to reproduce this on Linux.

[mcollina]

I think it's this block: https://github.com/nodejs/node/blob/master/lib/console.js#L81-L87.
What I think is happening is that there are a bunch of writes that are about to error, and we add a lot of 'error' in the meanwhile.

[mcollina]

I can reproduce it on Mac OS X, you just need to wait some seconds before hitting q within less.

[mcollina]

My fix is working, I'll send a PR soon.

[mafintosh]

@mscdex I'm also on linux and can reproduce. --trace-warnings solves it for me but when other users report a memleak or you get a hard to reproduce one it would be nice if a stack happened per default.

[mafintosh]

Thanks for the quick turnaround everyone :)