(node) warning: possible EventEmitter memory leak detected. 11 listeners added

[DmitrySoshnikov]

We tried switching from Q to bluebird in the Jest project, and started constantly to get this warning:

(node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit.
Trace
  at process.addListener (events.js:160:15)
  at process.on.process.addListener (node.js:802:26)
  at /Users/dmitrys/jest/node_modules/bluebird/js/main/async.js:80:25
  ....

We ran many tests in parallel, seems many promises are created, but Q didn't have this issue.

[DmitrySoshnikov]

We can fix it in our code by setMaxListeners(n):

process.setMaxListeners(0);

Although, probably bluebird may want to do the same in here.

[bgw]

I'd argue this isn't something that bluebird should do, as it has global side-effects, and because it can already be fixed on the application's (or in this case, jest's) side. Plus, it might cover up real leaks, though 10 seems like a pretty arbitrarily low value. We probably only get the error in jest because of the software's complexity.

[benjamingr]

Bluebird is just adding 1 handler here (per instance) if I understand
correctly so it's really not up to bluebird to put that limit at a very
high number because as the previous comment said it might cover up a real
issue.

On Tue, Jun 23, 2015 at 8:17 PM, Benjamin Woodruff <notifications@github.com

wrote:

I'd argue this isn't something that bluebird should do, as it has global
side-effects, and because it can already be fixed on the application's (or
in this case, jest's) side. Plus, it might cover up real leaks, though 10
seems like a pretty arbitrarily low value. We probably only get the error
in jest because of the software's complexity.

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[bergus]

Well, Bluebird could do

if (process._maxListeners)
    process.setMaxListeners(process._maxListeners + 1);

if there is really a need for this.