Question

When a request comes into a nodejs server, how does it handle the request?

I understand it has a different way of handling requests, as it doesn’t spawn a new thread for each request (or I guess it doesn’t use a traditional thread pool either).

Can someone explain to me what is going on under the hood, and does the flavour of linux matter here?

Answer 1

Node tells the operating system (through epoll, kqueue, /dev/poll, or select) that it should be notified when a new connection is made, and then it goes to sleep. If someone new connects, then it executes the callback. Each connection is only a small heap allocation

It is “event driven” where it handles IO in an async fashion (non blocking I/O). It internally does threading needed to do epoll, kqueue, /dev/poll, or select handling, but for you as a user/client it is absolutely transparent.

e.g. epoll is not really a thread pool, but an OS’ I/O event notification facility, that node.js sits on top of.