Non-blocking I/O and how Node uses it, in friendly terms: blocking vs async IO, CPU vs IO

The work of fulfilling a request can be split into two pieces: CPU work, which is actively running code and performing calculations, and I/O work, which is waiting for something else to happen. Normally, threads performing I/O must wait until the I/O is complete to continue processing, which is called blocking or synchronous I/O. Non-blocking or asynchronous I/O is an optimization available in some technologies (NodeJS, Java NIO, and others) that allows threads to move on to other work while the I/O is happening in the background.
Feel free to ask questions in the comments below!
00:00 Intro
00:31 Servers & Threads
01:28 A Server Is Like A Restaurant
03:22 A Request Has CPU work (active time) and I/O work (inactive time)
04:27 Code Example
05:03 Nonblocking I/O Timing Diagram
05:29 Blocking I/O Timing Diagram
06:01 Why Isn't Nonblocking I/O More Common?
06:47 Downsides Of Nonblocking I/O
07:42 Recap

[@amstud]

This is easily the best programming video I've ever seen. You took a subtle and tricky concept (one which I suspect most software engineers don't actually understand), and explained it simply enough that a child could understand. Not to mention excellent production values. Super excited to have found this channel, and I can't wait to see what you make next!

[@faraitanekha2642]

No need for me to leave a comment, then. You've said it perfectly my friend 👍😁

[@lauraablitt6379]

10000%. Honestly great video - thank you

[@fourteensierra]

Thought you did a fantastic job explaining Non-blocking I/O. I was super bummed when I saw you only had two other videos. Makes some more vids!!!

[@StudyingWithAlex]

I will :)

[@sepg6266]

Great job One suggestion: try a background video with less volume, no lyrics (human sound), and slower beats. That music is not just supposed to make the viewer excited or attracted, just makes it a lill colorful. Thanks

[@LyadhKhorEngineer]

Great video. Cleared up a lot of confusion regarding how javascript works as a single threaded server. 👍🏼

[@StudyingWithAlex]

Glad you liked it!

[@sid6576]

Just found this video, great work man. My 2 cents: I think the conversation about asynchronousity is incomplete without thinking about how threads and context switching are handled at the OS level. Without the concepts of yielding, interrupts and a priority queue for threads, I was confused for the longest on time on how the computer just magically knows when to switch from one task to another and when it knows that an IO task is complete. I feel like the next step after this video would be to tackle scheduling in OSes because I feel like a lot of programmers on the internet find it to be impenetrable when it's really not that hard!

[@wafikiri_]

I agree. I watched the video expecting a more advanced explanation. I'm currently amateurly designing the scheduler of a multi-tasking processor and wanted to learn of current solutions.

[@jordanbtucker]

Loved the analogies and animations!

[@IvanBilan-ty9jw]

It's a great explanation of complex concept. Divinding work time into CPU and IO time is a realy great concept for understanding this. Now I understand why Node.js is so popuar for web development. Thanks!

[@iganic7574]

Great explanation , finally I understood what is non blocking I/O . 🙌

[@avgsteve]

This is how the knowledge should be taught. Thanks for sharing

[@ninthsun]

Seriously, this video should be the must for every beginner learning nodejs. Super important concept, but in super easy words and animations.

[@RebienKani]

Dude amazing video and excellent job on explaining this topic because it was true hassle for me too understand. Just a couple of tips for in the future: 1: Choose a different music with lower BPM and lower it by 20% 2: A better microfoon or remove static noise in post production For the rest killer video!!!

[@asepulven2768]

Excellent Video! best explanation so far with visual representation.

[@vertikasrivastava1186]

This was super helpful, thank you!

[@matthewoluwafisayoadeniyi9803]

Just what I needed. Thanks mehn

[@julianhu]

This is absolutely the best explanation video about async I've ever seen. Amazing work!

[@Priyanka-hs5jk]

This is the most crisp and clear explanation for non blocking I/O in layman terms, thanks a lot

[@dark_lord98]

This is the best video I watched regarding the I/O and CPU tasks. The code example cleared many things for me. Thanks a lot man. Please keep making videos on software engineering topics.

[@flucksy119]

i think this is the best computer science video ive ever watched with regards to visually understanding due to the graphics

[@georgemarwanqana3478]

BEST EXPLANATION OF THE YEAR

[@MyAminedz]

Absolutely mind-blowing video, hats off to you sir

[@congdao7484]

Good work, hope you have more similar video.

[@brandonhunter2074]

This is one of the best explanations of this concept I've ever seen. Well done!

[@nathanielkswas]

This was super well presented and produced. Keep up the good work!!

[@alaaroumeeh2752]

Thank you very much no one explains this topic well, or they don't explain it at all!

[@souravsharma6092]

Thank you! Really glad I landed on this video, I don't remember the last time someone explained things as simply and effectively as this. Keep up the good work! Will regularly check your channel for any doubts.

[@tayyibulhassan6227]

I HAVE NEVER SEEN A BETTER TUTORIAL THAN THIS ONE DUUUUUDDDEEEE, YOU ARE AMAZING!!!

[@carolinafransiscalopezpaca541]

you make great content, don't stop until the top

[@indoor-adventurer]

dude, make more videos! Such high quality stuff 👏

[@ainharansubramaniam2910]

Great video I hope you keep them coming

[@sandeepkosta5750]

I just wanted to break the like button by clicking on it many times. What a great explaination sir Thanks so much

[@imaazk]

I usually don't comment. but you really make things very simple to understand. Thank you!

[@dhruvpurwar6642]

One of the best videos for the concept!!!

[@minhtaile3572]

Thanks for making this video, it's easy to understand

[@mandaputtra]

Thanks, all of your video are easily digested! Maybe you can decrease the background music volume to 10% or 20%.

[@muhammadsalikin3886]

Thank you so much for this video. Best explanation ever !

[@theace9562]

Super helpful. Thanks

[@Finn-jp6pn]

Found this on Reddit. This was really helpful. Thanks 👍

[@wichaisawangpongkasame9237]

You're great at explaining things. It's much clearer to me now. Thanks.

[@brettwines6812]

wow, each of these is better than the last. Your hard work really shows!!!

[@mars_bold]

BROTHER, YOU ARE THE BEST!!! You oooh really helped me!! THANK YOU VERY MUCH!This is cool, well done!

[@teamjupeter9451]

What a wonderful lecture on blocking!!

[@whitebeardpirates7551]

Man that's HUGE, i finally understand this heavy topic as if it was a piece of cake, you're the GOAT ♥♥ Thanks for your effort ♥

[@saurabh95mishra]

amazing explanation, I learned redis uses similar model as nodejs, would love your video on that!

[@nicholasaine7756]

Best explanation I have come accross, on this topic.

[@lychenus]

very decently explained. now i understand when to pick a (non-)blocking io framework

[@cvramankishore4u]

Great explanation saw couple of your videos and both are awesome keep up the good work

[@teerapatprommarak2070]

Fantastic video! Thank you Alex

[@ckim0324]

Fantastic video, Alex. Your channel is VERY underrated.

[@island_rhythms]

This is a treasure! Such a great and simple explanation! Thank you

[@morphos2]

Bravo!!! Excellent explanation!! 👏👏👏

[@yooog]

Excellent explanation!

[@aramaiskhachatryan553]

Great one! Keep it up Alex.

[@karthiks-he4wh]

Beautifully explained 👌

[@saurabh0241]

thank you soo much for this video brother . love from INDIA

[@ashishchiluka8912]

Great explaination , one of the best videos

[@rollercoasterer]

Very top notch quality!

[@cuongtrinhminh]

Great video because it explains a hard thing simple

[@Y3arin]

Great work. This is easily the best, clearest explanation of the subject I've seen in a video.

[@lgodlike2324]

You just explain it so well ! This is exactly the video I need.

[@ytrkptl]

Great explanation.

[@yashkumar-jv2cf]

I was struggling with this concept for months. you cleared my doubt. thanks man

[@samartajshaikh2601]

Great explanation. Simple and precise. Exactly what I needed. Thanks.

[@artnovikovdotru]

First of all, thanks, very good animation. But, it misses an important point. Blocking IO isn't really blocking. Request goes to sleep mode when it waits for IO, giving resources to other threads - if following your analogy, the waiter's soul jumps into another waiter to do stuff, while the first one is waiting (sleeping) for customers to read the menu, etc. And you can have tons of threads to serve as many customers as you can possibly have. However, in reality, there is context switching between threads, and between threads and kernel. And this is what makes this approach slower. This is the most interesting part which I've never seen yet anybody covering in understandable way.

[@StudyingWithAlex]

Blocking I/O is blocking in the sense that the thread performing I/O is occupied and can't work on other tasks. Like you said, the thread is sleeping and doesn't take up much compute resources, but it's still occupied. That's why blocking I/O with low thread count causes CPU underutilization and request slowdown, and why as I mention in the video, folks using blocking I/O usually crank up the thread count to compensate, but that has its own drawbacks as you mention.

[@artnovikovdotru]

@@StudyingWithAlex Yes, bascially you described the video and my comment again ;) What I'm saying is that one could think that "hey just increase thread count and no need to care about non blocking io, ugly async programming etc" but increasing thread count creates problems, and that's the most interesting part, because it's exactly the reasoning behind non blocking i/o, but no one can explain it properly in details. I.e. everybody just have to trust that threads have drawbacks, but no exact step by step comparison.

[@siddharthyadav5066]

This very well explained the concept with animations and examples. Thanks for the great work

[@Frozd]

Great video! The explanation was on-point and easy to understand, and the animations made it easy to follow.

[@mohamedchebbi1154]

That's huge, great job, u saved my life.

[@utkarshtripathi2349]

Best explanation, Thanks for the video

[@Karpefilm]

By far the best explanation! Keep up the fine work

[@jokercry8132]

Wow! Explanation is so good with the graph.

[@arjunbhat6502]

Keep on doing such kind of videos. That really helped.

[@Juan_lauretta]

Wow this video was amazing, thank you so much

[@janetspellman3945]

Thanks so much, this was super helpful!

[@vunu.]

Your voice is perfect for these videos! You've come so far in the last decade, awesome stuff! Works like clockwork...wink wink nudge nudge. Anyway, I enjoyed this. I'm subscribing and hitting the bell!

[@user-gc4xs1qy1o]

nice explanation! Thank you! Alex!

[@jmro7]

top notch content. i can already envision this being a big education channel. Keep it up !

[@fahad_hassan_92]

Great video Alex thanks!

[@vyasrajjoshi6059]

Very well presented. Waiting for more of such content 😊

[@henriquesenadev2194]

Incredible video!

[@howards5205]

This is the best explanation I've seen on non-blocking I/O. Thank you SOOOO much for this video! It clarified so many questions I had. @4:20 of your video, you listed three examples of I/O (inactive time): - reading from filesystem - making network requests - waiting for time to pass Would executing a long-running database query qualify as a I/O or CPU? The database would be doing all the heavy compute. Would NodeJS be able to move onto other active tasks while the database query is running? Or will a thread be tied to the database query?

[@ShaikSameer549]

Thanks for making it simple and more understandable

[@waniarifrasool]

This is wonderful!

[@dmitry027]

Great explanation!

[@icns01]

It was super helpful. Thanks much for clarifying.

[@raimundoladrondeguevara8597]

Thank you so much for this video.

[@Belkiii88]

Really great video!

[@salvadorgonzales1566]

Wow you did very good on this video! well explained! hope you make many more on all topics lol

[@Simplicity4711]

Really great video, but I highly recommend using background music without vocals, or it gets much harder following what you say. 😊😉

[@oladipupooladele3647]

Great video!!!!! i loved it so much

[@michaelciyke]

awesome explanation!

[@flavioneto1081]

Great video and animations, very explicative, thank you

[@arnabgoswami8971]

Thanks you so much for the wonderful explanation It really helped me clearing the concept

[@t2a392]

Amazing video !

[@Developerish]

My gosh, where have you been my whole life.

[@ayushmanvashishtha8180]

Great video man

[@DharanAditya]

Thanks for the video ❤

[@idanqwe1]

Great explanation! Thank you.

[@minhhieple6483]

Thank for sharing

[@user-nh2xc6rd5c]

awesome video bro!

[@waagnermann]

best video ever!!!

[@prabhat9274]

great explanation...