Thoughts filed in: Node.js


Node.js itself is blocking, only its I/O is non-blocking

I've recently been getting my feet wet, playing around with Node.js (yes, I know – what took me so long?). I'm having a lot of fun, learning new technologies by the handful. It's all very exciting.

I just thought I'd stop for a minute, however, to point out one important detail of Node.js that had me confused for a while, and that seems to have confused others, too. More likely than not, the first feature of Node.js that you heard about, was its non-blocking I/O model.

Now, please re-read that last phrase, and re-read it carefully. Non. Blocking. I/O. You will never hear anywhere, from anyone, that Node.js is non-blocking. You will only hear that it has non-blocking I/O. If, like me, you're new to Node.js, and you didn't stop to think about what exactly "I/O" means (in the context of Node.js) before diving in (and perhaps you weren't too clear on "non-blocking", either), then fear not.

What exactly – with reference to Node.js – is blocking, and what is non-blocking? And what exactly – also with reference to Node.js – is I/O, and what is not I/O? Let me clarify, for me as much as for you.