Understanding NodeJS & Non-Blocking IO

Question

So, I\'ve recently been injected with the Node virus which is spreading in the Programming world very fast.

I am fascinated by it\'s \"Non-Blocking IO\" approach and hav

Answer 1

Q1. " what does the job of lines 2 & 3 while the rest of the program is being executed?" Answer: "Nothing". Lines 2 and 3 each themselves start their respective jobs, but those jobs cannot be done immediately because (for example) the disk sectors required are not loaded in yet - so the operating system issues a call to the disk to go get those sectors, then "Nothing happens" (node goes on with it's next task) until the disk subsystem (later) issues an interrupt to report they're ready, at which point node returns control to lines #2 and #3.

Q2. single-thread non-blocking dedicates almost no resources to each incoming connection (just some housekeeping data about the connected socket). It's very memory efficient. Traditional web servers "fork" a whole new process to handle each new connection - that means making a humongous copy of every bit of code and data variables needed, and time-slicing the CPU to deal with it all. That's massively wasteful of resources. Thus - if your load is a lot of idle connections waiting for stuff, as was theirs, node makes loads more sense.

Q3. almost every programming language does already have non-blocking I/O if you want to use it. Node is not a programming language, it's a web server that runs javascript and uses non-blocking I/O (eg: I personally wrote my own identical thing 10 years ago in perl, as did google (in C) when they started, and I'm sure loads of other people have similar web servers too). The non-blocking I/O is not the hard part - getting the programmer to understand how to use it is the tricky bit. Javascript happens to work well for that, because those programmers are already familiar with event programming.