How to hold a response? And are there something called "maxHeldResponseCount"?

1. I want to implement a long-polling model in my server (express.app).
2. I use a map to stored incoming response, waiting (about 60 seconds later) another request to finally send stored response back.
3. I find the store action will block other incoming request. I mean, the callback of `app.post("xxx"...)` is not called until I close some of stored responses in step 2.

So, I wonder:

1. Is it a right method for me to store response from `app.post` to implement long-polling?
2. Does express.js itself set max concurrent count of held responses?