Real-life examples of async non-blocking loop vs. multithreading?

Question

I have been developing in Node.js recently and have a good idea of what is going on as far as the event loop. Given that I had experience with javascript, Node made sense for me to use, but I wonder, has anyone ever stopped using a multithreading system and went to async for PERFORMANCE? Or made a choice to go with async instead of multithreading for performance?

What are real-life examples of async non-blocking I/O triumphing over multithreading in the real world?

Answer 1

Regardless you do multithreading or not, all modern operating system I/O operations are inherently async. So saying that "async is faster" is not actually true. However, async programming allows you to conserve threads with almost the same performance. That's important on a server because number of threads you can get is finite (limited by available memory).

So with async you don't necessarily get better performance but better scalability on I/O heavy tasks. Async could even perform worse on CPU-intensive tasks since you don't benefit of parallelizing work between server cores. I/O on the other hand, works with interrupts and DMA which does not involve CPU. That's how you can get good-enough performance because you can keep executing until hardware notifies you of I/O completion by signaling an interrupt.

Edit: I just figured out that I did not answer your actual question. But as long as you know how async benefits you, you may not need real world examples on that. Just know that:

• communicating with database is I/O
• reading from or writing to disk is I/O
• sending/receiving packets over network is I/O
• the rest is CPU

Depending on if you use I/O or CPU more async could give you great scalability or worse performance. Typically web applications are I/O intensive, which benefits from async programming.

Answer 2

It is easier to code, because you do not need to manage consistencies/data exchange between multiple processes/threads.
There is no real advantage for this model when creating just a simple web application, but when having a server managing multiple connections at the same time, where the data that is passed is somehow tied together.

Perfomance-wise there are some advantages because having multiple threads/processes tend to use way more memory than just a single thread.
Simple math: Having one thread handling one connection and each thread needs 1MB in RAM it is very easy to figure out how much connection you could on one computer. With node.js you have one process handling multiple connections and it takes for example 20MB in RAM and 4kb per new connection. I think you get the idea.
Async I/O is not faster, but it helps you consume fewer resources while doing the same thing multple times at the same time.