Writing async/await from scratch in C# with Stephen Toub

Join Stephen Toub and Scott Hanselman as they dive deep into the world of .NET. On this first episode, Stephen and Scott demystify the world of asynchronous programing with .NET and specifically the magic behind async/await, something that developers use every day. To do so, he builds his very own implementation of async/await completely from scratch and explains throughout the way. If you are looking to go deeper with .NET then you are in the right place.
Chapters:
00:00 - Intro
03:00 - Understanding concurrency, parallelism, and asynchronous
08:30 - Creating our own ThreadPool
26:00 - Creating our own Task
45:30 - Putting together ThreadPool and Tasks
56:00 - Async iterators and yield
01:05:00 - Wrap-up
Resources:
Blog: devblogs.microsoft.com/dotnet...
Docs: learn.microsoft.com/dotnet/cs...
Final Code: gist.github.com/jamesmontemag...
Connect with .NET:
Blog: aka.ms/dotnet/blog
Twitter: aka.ms/dotnet/twitter
TikTok: aka.ms/dotnet/tiktok
Mastodon: aka.ms/dotnet/mastodon
LinkedIn: aka.ms/dotnet/linkedin
Facebook: aka.ms/dotnet/facebook
Docs: learn.microsoft.com/dotnet
Forums: aka.ms/dotnet/forums
🙋‍♀️Q&A: aka.ms/dotnet-qa
👨‍🎓Microsoft Learn: aka.ms/learndotnet
#dotnet #asyncawait #csharp

[@majixx]

Stephen Toub is an absolute treasure for all .NET developers. We defiantly need more content from him. What a great orator and teacher!!

[@FilipCordas]

You have to give credit to Hanselman as well he is the best at preventing not to know anything when in fact he is probably as knowledgeable as Stephen.

[@davecenter2002]

I love Hanselman and he’s fantastic, but he absolutely is nowhere close to as knowledgeable as Stephen.

[@shanselman]

@@davecenter2002can confirm. We have different jobs. Plus he kinda wrote the thing. 😂

[@michaltomorowicz596]

when you have two legends in one vid, debating who is a bigger legend is like arguing which type of sugar is sweeter :D awesome content

[@san30911]

Totally. He made me fall in love with C#...

[@elerius2]

More of this, please! Feels like a channel9 video from back in the day.

[@dotnet]

Oh we got more!!!

[@theFijian]

Lol Channel9 really does feel like "back in the day" 🤣

[@vacc1001]

@@dotnet Is there a place where I can find more videos like this?

[@dotnet]

@@vacc1001 We are releasing more and more. Subscribe and checkout the playlist: kzbin.info/aero/PLdo4fOcmZ0oX8eqDkSw4hH9cSehrGgdr1

[@tomglenn6019]

I was already very familiar with how tasks/async/await work under the covers but seeing Stephen effortlessly "reimplement" it without copying and pasting or using notes is a humble masterclass of intellectual horsepower.

[@Daysra]

Can I just say how great this duo is. Stephen is awesome at explaining things to a great depth, and Scott knows exactly where to stop and ask for clarifications, at an extent that hits just the sweet spot for me, not being too much. More videos from this duo please.

[@s.hosseinhosseini8330]

This was amazing. Why I love this? 1. Scott Hanselman 2. Stephen Toub 3. An actual deep dive into a concept with a high-quality explanation of it.

[@computer9764]

3.1. It didn't have a ridiculous thumbnail.

[@gpltaylor]

When I say that I have watched every video and read every article about async and await, I am not exaggerating. However not a single one has come close to educating what this does, why and how to use it and how this is implemented as this does. This is one of the best videos I have seen on this subject. I would love to see more videos like this, that deep dive into the technical rather than floating around at surface level

[@ghostg6107]

Kevin Gosse also did a deep dive on async await. Stephen Cleary has a walkthrough of the history of Task.

[@tedchirvasiu]

I love how Scott asks all the right questions.

[@shanselman]

❤

[@Anubis_moe]

Wow we need more topic like this please. We need more of .net core internals

[@dotnet]

Oh we have more!!!!!

[@umarahmad3705]

Looking forward to more ​@@dotnet

[@umarahmad3705]

​@@dotnetor do you already have a playlist with topics like this

[@umarahmad3705]

Strongly agree

[@ThorstenSauter]

This was an absolute delight to watch. Thank you Stephen and Scott!

[@CecilPhillip]

Great video. Would love to see a dive into IAsyncEnumerable implementations

[@dotnet]

Thanks for the idea! Hope you are doing well Cecil 💖

[@ChaseFreedomMusician]

@@dotnet I would love to see an example implementation of IQueryable, it is so non-approachable even for simple tasks, but it is an incredibly powerful feature.

[@WespazjansDad]

Superb stuff. Scott leads it well, without interrupting too much. And Stephen delivers pure meat. That is one of these few precious resources that despite the fact they last for ah hour, I personally need a few hours to analyze, rewind and make sure all these topics really click in my head.

[@runtimmytimer]

Love this deep dive stuff. Too much 101 content and almost zero 400 content.

[@ArnonDanon]

Scott & Stephen rewriting async await reminded me David & Damian rewriting SignalR on stage. All dotnet devs out there are standing on the shoulders of Giants🙏🏼 This is great content

[@metaturso]

Link please?

[@pmnm113]

after watching this I am youtubing about Stephen Toub videos. We need more content from him. I was nice to see low level design of async await here. thanks!

[@MatthiWare]

Amazing video! I would love to see more content like this.

[@cheekychappy1234]

Such a fantastic video! Keep producing more and don't be afraid to dive deeper and deeper.

[@JSWarcrimes]

Now this is some premium content.

[@bity-bite]

Great video! I love this style of rewriting stuff to explain how it works internally. We'd love more videos like this one

[@DannysGalaxyTab]

What a great video idea. Great hosts to listen to as well.

[@zksward]

Really love to see this kind of in depth content coming from the team. We need mooooore!

[@fullemptiness]

What a great idea to teach such a complex topic! It's like you found the missing piece in my (most .NET devs?) understanding to async programming!... Please do a series on async programming like this episode. Thanks!

[@acedonk]

This was a masterclass, thanks!

[@minimalistdeveloper]

Loved this. This is the video equivalent of Csharp in Depth and CLR via Csharp. Kindly do more of these level 300 topics.

[@CraigShearer]

Great info. Been away from C# for a few years, but nice to see this detailed as to how async/await works.

[@FXK23]

Definitely going to watch this again and code along. Excellent video!

[@paaabl0.]

Brilliant demo! Thank you guys!

[@codewithkhondamir]

That’s amazing. Thanks Scott and Stephen.

[@fredyjimenez4853]

This is best explanation to fully understand async/await. Greate quality content Kudos to Scott and Stephen

[@StephenGierek]

This was really great! I've always struggled wrapping my head around how async/await works, but this method of instruction is extremely effective in conveying what's going on under the hood. Please, more like this. I could watch these all day long. 🙂

[@ChaseFreedomMusician]

This is by far one of my favorite videos to-date.

[@Hereson]

Amazing explanation, please do more of these!

[@pachanga5382]

Excellent video-I was wondering at first why I needed to know this, and now I know!

[@SlackwareNVM]

This was fantastic! I'd love a couple of more episodes that go into the optimizations that can be layered on top of this implementation.

[@--Eric--]

Thanks Stephen and Scott, this was a great session. More please... 👏🏼

[@VukManic]

What an amazing video! This is one of best video to understand async await!!!! Thanks to both of you! Really enjoyed it!

[@moke_codes]

This was amazing! I wish we could see more advanced topics like this. Learned a lot! Thanks guys!

[@krccmsitp2884]

Amazing! Thanks to both of you! 🙂

[@vedantkoditkar5968]

If only there is a way to give million up vote to this video. I always look forwards to Stephen Toub videos, his explanation is top notch.

[@stevanfreeborn]

Thank you for making this! 🙏🏻

[@fifty6737]

awesome video, always pleasure to listen to stephen

[@neeleshbodgal7479]

That helps to understand more and better about the Task API. Stephen Toub blogs are worth reading that always teach me something new 😀

[@robl39]

Now get David Fowler to write Kestrel from scratch. I’d love to see that.

[@v001]

Stephen Toub is a legend! great talk, need more of this

[@papafe]

Super interesting! I think it would be interesting also to dive deep into SynchronizationContext and how it relates to the ExecutionContext that was shown in the video

[@danfriedman7009]

Immensely helpful. You guys rocked this presentation. Can't wait to watch the LINQ videos (and I hope there is more on the way).

[@emiraksoy1520]

This was amazing we want more content with Steve 💯💯

[@mambocollective]

Great video. Learnt so much from this. Definitely need more content like this, especially with Stephen. It worked so well with him leading the way and then you pulling him back with questions I had in my own head. Looking forward to more of this sort of content.🤩

[@RickJohnn]

Excellent from start to finish.

[@SharpGIS]

Loved this. Please do more Level 3-400 content!

[@damianpio1443]

Loved this video, hope we will get more of these

[@DotNetRyanYT]

Thanks for this. Async/await was always a black box to me, but now I feel I have lifted the lid on the box and took a look inside.

[@imranhussain8700]

This is some crazy stuff. Stephen Toub is amazing. Scott Hanselman has done a fantastic job as usual for the viewers to ensure the topic is covered as much in depth as possible. Thank you very much. We need morrrrrrrrrrrrrrreeeeeeeeeeeeeeeeeee of these for sure.

[@TheProTip]

This is great. I've never actually heard Stephen talk though I've read a bunch of his perf reports and other posts. He presents very well.

[@sudeshryan8707]

This is gem of a tutorial. Thanks guys

[@danielvillalba4457]

Wow, just amazing information and even better way to explain it! Thanks

[@chenc671]

Wow, It was a Master piece when the await works at the end !

[@kRySt4LGaMeR]

Watching Stephen doing this is amazing. Scott on the other hand has extremely lack luster contributions.

[@paulecampbell]

Stephen is on another level!

[@thedanielspindler]

Loved this. Amazing! Now I just need to re-watch it another 5 times at 0.5 speed to really soak it all in.

[@sjark5000]

This is just fantastic content, more of this please :)

[@SajadJalilian]

We really need Stephen do more live coding. He is really good at delivering what he does

[@michaltomorowicz596]

What a great material guys, massive kudos.

[@giovannimorleschi1750]

Awesom, semply awesom, you have to do a lot of this video please! Stephen Tuob, you are ten thousand time better then the better professor in tis solar system!

[@northshorepx]

That was a really great tutorial. Seeing how everything is continuations all the way down was incredibly eye opening. I'd love to see more details like this please. However I have one small nitpick, that of Stephen constantly making the font way too small to read. Scott kept picking him up on it, but it's really important for us who are watching to be able the read the code that they're writing and thus for presenters to realise how video tutorials need zoomed up fonts.

[@wolfgangdiemer2511]

Thank you very much, awesome content

[@DOTNETMAN]

The Legends of .NET.

[@KenRossPhotography]

Awesome video - so many great nuggets here. Even if you think you *know* async/await, you'll get value from watching this (maybe more than once) 🙂

[@unknown.artist.track3]

I had already bookmarked your article from dev blog about async await)))

[@BryanKelly]

First, I loved this video. Just everything about it was good. I would love a follow up to cover: 1. more of the async/await keywords (the stuff you were getting to at the very end) 2. Why doing the "bad" things is bad. (ex. .Result, and others I'm failing to think of now) 3. Async enumerable

[@theFoodieCyclist]

Loved it! You guys are awesome!

[@AslamNazeerShaikh]

Please make videos on "cancellation token"

[@zakizaz1]

Great content . Thank you

[@thishandleistaken]

Amazing video! Thanks!

[@jackkendall6420]

This was incredibly good.

[@MatteoGariglio]

I wish I watched this video long time ago 😅. Thank you so much Stephen, the explanations are really instructive.

[@rasmussoeborg450]

Very informative - Great explanation

[@stephajn]

Like Admiral Kirk said to Saavik in Wrath of Khan, “You have to know WHY things work on a starship.” This was definitely really cool to watch and follow! Gonna have to watch it again on a PC as opposed to my iPad, but it is well worth it!

[@timeless-sg]

EXCELLENT. THANK YOU STEPHEN.

[@jimiscott]

This is superb.

[@user-we2gj9uz7r]

Excellent content! Thank you!

[@rafaelfelipe3986]

Amazing content. Thank you so much for that.

[@sachinvshishth]

Thank you for the insightful session. Just a quick request: could you please utilize the dark theme whenever feasible?

[@azarthi]

Love this super easy to follow!

[@PhoenixCustomerInsights]

I would love to strive for that clarity of knowledge in tasks. I'm holding on to this video for another review and letting it wash over me a few times. Could there be a continuation in the parallel processing of tasks, comparing concurrency and parallel execution of Tasks?

[@brechtlaitem]

We want more, we want more!!

[@dotnet]

We are making more right now!!!!!!!!!!!!!!!!

[@semihartan]

Amazing presentation. Thank you both!

[@obinnaokafor6252]

Scott and Stephen should do videos on Tensor Primitives in dotnet. And other ML types and improvements in dotnet and C#

[@shanselman]

Totally!

[@tarun-hacker]

Stephen Toub is awesome.

[@LILogisticaIntegrada]

Thanks for this!

[@aptypp]

Thanks for video!

[@shadowspyes]

please more high detail low level videos like this!

[@karthiks4347]

Simply great!!👍

[@Dotnetawy]

Awesome 👌

[@dealsman]

Intense! Both of you!

[@tiZyJoshi]

this was awesome, ty!

[@Rolan18111]

Excellent video - that certainly removed a lof of the "ghosts in the machine" feel of async/await. I feel like de-implementing syntactic sugar would be another good video topic. Take some modern c# code and replace all the syntactic sugar with the underlying implementations. And/Or show how you can look up the underlying implementations quickly & easily.

[@familienmitic6623]

Scott is just awesome

[@ralmslb]

This one deserved a part 1 and part 2, to better go on a slower pace around the await keyword, etc. Felt that was mostly just around Tasks, that is inherently to async await, but still, doesn't allow to have a good peak on await functionality and nuances.

[@tedchirvasiu]

Wow, just as I needed this

[@MatPolutta]

I needed this. Thanks

[@MatPolutta]

Just watched a 2nd time. Almost there. 3rd time is the charm? Let's hope.