Learning Golang: Context package: Cancellations, Deadlines and Request-scoped values

Рет қаралды 11,537

Күн бұрын

Welcome! Let's learn and talk about the context package, specifically about how to implement deadlines, cancellation and request-scoped values using the functions defined in the package:
* context.WithDeadline and context.WithTimeout
* context.WithCancel and
* context.WithValues
The code is available here: github.com/MarioCarrion/video...
* Blog: mariocarrion.com/2021/05/31/l...
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00:00 Intro
00:56 What is the context package?
01:19 Context Deadlines
04:06 Cancellation Signals
07:32 Request-scoped values
10:02 Best practices
11:17 Parting words
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Пікірлер: 18

@MarioCarrion 3 жыл бұрын

*Blog* mariocarrion.com/ *Building Microservices in Go* kzfaq.info/sun/PL7yAAGMOat_Fn8sAXIk0WyBfK_sT1pohu *Go Tools and Packages* kzfaq.info/sun/PL7yAAGMOat_HEEOvH99agDs_5g51A0Ls3 *Testing in Go* kzfaq.info/sun/PL7yAAGMOat_HSeW4zF0uRL9EaHadE4ZZq *Keep it up!*

@robertjmccabe Жыл бұрын

I like your examples. They are very clear and to the point.

@hectorclara8894 2 жыл бұрын

Hola Mario, Thanks for making such great videos, they have helped me in my current job with working with golang. I come from JS / Ruby land and typed languages can be quite confusing but I see the appeal. Your videos are great for me personally and I have learned a lot and applied it to my career. It's really great to see someone who has such passion for their work, I hope to be like that one day, since I'm pretty junior, I admire those who can "think quickly" and come up with solutions, I hope to be that kind of person one day.

@MarioCarrion 2 жыл бұрын

Hola Hector! I'm glad you're finding the videos useful. IMO they key is all about practice and understanding there's always a learning curve, you just have to trust the process.

@hectorclara8894 2 жыл бұрын

@@MarioCarrion El processo duele D:

@renatospaka 2 жыл бұрын

Thank you for this class. Finally I understood what context is and how to work with them. No, it is not dark sorcery...

@MarioCarrion 2 жыл бұрын

Thanks for watching Renato. Take care.

@SirRFI 3 жыл бұрын

Do you have to use select-case syntax for this, or are there other options? Here's an example I have in mind: func main creates context with deadline, like in the example, then creates anonymous function (which does some job, for example waits 1 second) and calls it with goroutine, then blocks at ctx.Done() (assuming it's blocking operation), waiting for deadline (for example 2 seconds). How can I make the anonymous function mark that the task has been completed? Should I call cancel()? What happens to the "defer cancel()" in such scenario?

@MarioCarrion 3 жыл бұрын

There's no need to use "select" for "context.WithCancel". "WithCancel" acts more like "Whenever the returned CancelFunc is called everything using the derived context will cancelled", so if there are any calls using the derived context then all of them will be cancelled. Regarding the other question, perhaps you may want to explore the package "golang.org/x/sync/errgroup" it allows coordinating goroutines much more easily.

@HasanAYousef 2 жыл бұрын

Great, a side question, what is the theme you are using at your terminal?

@MarioCarrion 2 жыл бұрын

I'm using the default theme in iTerm2, but I'm using starship (starship.rs/) as well, if you mean vim I'm using "NLKNguyen/papercolor-theme"; hopefully that answers the question. Best!

@user-mw4mt2mt1r Жыл бұрын

So, basically the cancel() is working as a return statement for a goroutines? Which allows them to call the code ending the goroutine from outside?

@MarioCarrion Жыл бұрын

Yes, although I'd rephrase it a bit: cancel() will tell all goroutines using the same context to "finish"; and it's up to the goroutines to honor that.

@SirRFI 3 жыл бұрын

I think that the explanation for WithDeadline and WithTimeout in the example is overlapping (if that is proper term) - you showed how it works, but not what is the difference. The documentation says "WithTimeout returns WithDeadline(parent, time.Now().Add(timeout)).", and the way I understand is: WithDeadline asks you for absolute timestamp when it should expire. It can be expressed as "it should be done by 2021-05-10" (specific date). It can be also calculated off something, like relatively to current time - "if it's not done in 10 minutes, I am leaving". WithTimeout is abstraction or wrapper for WithDeadline, which covers common scenario of setting the deadline from current time, so you don't have to do "time.Now().Add(duration)" every time by hand - you only say how much time you are giving it (the "if it's not done in 10 minutes, I am leaving" scenario). Is this correct?

@MarioCarrion 3 жыл бұрын

In the diagrams I meant to explain the parameters, but really in the end both of them work the same, and yes, you're right "WithTimeout" adds the value to "time.Now()" and calls "WithDeadline" (see go.googlesource.com/go/+/go1.16.3/src/context/context.go#502), it's sort of like a helper.