What happens when a single request takes a long time with these non-blocking I/O servers?

With Node.js, or eventlet or any other non-blocking server, what happens when a given request takes long, does it then block all other requests?

Example, a request comes in, and takes 200ms to compute, this will block other requests since e.g. nodejs uses a single thread.

Meaning your 15K per second will go down substantially because of the actual time it takes to compute the response for a given request.

But this just seems wrong to me, so I'm asking what really happens as I can't imagine that is how things work.