How node.js works?

Question

I don't understand several things about nodejs. Every information source says that node.js is more scalable than standard threaded web servers due to the lack of threads locking and context switching, but I wonder, if node.js doesn't use threads how does it handle concurrent requests in parallel? What does event I/O model means?

Your help is much appreciated. Thanks

Answer 1

Although Question is already explained before a long time, I'm putting my thoughts on the same.

Node.js is single threaded JavaScript runtime environment. Basically it's creator Ryan Dahl concern was that parallel processing using multiple threads is not the right way or too complicated.

if Node.js doesn't use threads how does it handle concurrent requests in parallel

Ans: It's completely wrong sentence when you say it doesn't use threads, Node.js use threads but in a smart way. It uses single thread to serve all the HTTP requests & multiple threads in thread pool(in libuv) for handling any blocking operation

Libuv: A library to handle asynchronous I/O.

What does event I/O model means?

Ans: The right term is non-blocking I/O. It almost never blocks as Node.js official site says. When any request goes to node server it never queues the request. It take request and start executing if it's blocking operation then it's been sent to working threads area and registered a callback for the same as soon as code execution get finished, it trigger the same callback and goes to event queue and processed by event loop again after that create response and send to the respective client.

Useful link: click here

Answer 2

Node JS is a JavaScript runtime environment. Both browser and Node JS run on V8 JavaScript engine. Node JS uses an event-driven, non-blocking I/O model that makes it lightweight and efficient. Node JS applications uses single threaded event loop architecture to handle concurrent clients. Actually its' main event loop is single threaded but most of the I/O works on separate threads, because the I/O APIs in Node JS are asynchronous/non-blocking by design, in order to accommodate the main event loop. Consider a scenario where we request a backend database for the details of user1 and user2 and then print them on the screen/console. The response to this request takes time, but both of the user data requests can be carried out independently and at the same time. When 100 people connect at once, rather than having different threads, Node will loop over those connections and fire off any events your code should know about. If a connection is new it will tell you .If a connection has sent you data, it will tell you .If the connection isn’t doing anything ,it will skip over it rather than taking up precision CPU time on it. Everything in Node is based on responding to these events. So we can see the result, the CPU stay focused on that one process and doesn’t have a bunch of threads for attention.There is no buffering in Node.JS application it simply output the data in chunks.

Answer 3

Though its been answered , i would like to just share my understandings in simple terms

Nodejs uses a library called Libuv , so this Libuv is written in C language which uses the concept of threads . These threads are called as workers and these workers take care of the multiple requests from client.

Parallel processing in nodejs is achieved with the help of 2 concepts

1. Asynchronous
2. Non blocking IO