5 Fatal Coroutine Mistakes Nobody Tells You About

Рет қаралды 84,947

Күн бұрын

Coroutines are the preferred option for asynchronous programming in Kotlin if you ask me. Still, you need to know what you're doing, else it can quickly backfire for you.
This video shows you 5 common mistakes you rarely hear about when it comes to using coroutines.
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00:00 - Introduction
00:40 - Mistake 1
05:51 - Mistake 2
08:26 - Mistake 3
11:11 - Mistake 4
14:26 - Mistake 5

Пікірлер: 180

@SamRamezanli 2 жыл бұрын

I don't know how to express how helpful this video was. blogs and tutorials often tell us what to do, but it's important to understand what not to do as well. Looking forward to more videos like this

@PhilippLackner 2 жыл бұрын

Glad it helped! 🙏

@marksunghunpark 2 жыл бұрын

It's parellel dispatch and you can even use it for async mapper. You can make the code shorter if you want: val firstNames = userIds.map { userId -> async { getFirstName(userId) } }.awaitAll()

@pradiptapriya7546 2 жыл бұрын

Hi, do you mind answering some of my questions regarding this async? When using async and awaitAll() to get data, is there a chance that the order of name lists retrieved will be changing every time the operation is done? Because I thought since it's being done parallel, there's a time when some data in API are obtained faster than others, making the order of the list changing every time based on how the network performance is right? Or the list will be always the same?

@marksunghunpark 2 жыл бұрын

@@pradiptapriya7546 It's same with async { getFirstName(userIds[0]) } + async { getFirstName(userIds[1]) } + async { getFirstName(userIds[2]) }... So, it should be the same order.

@pradiptapriya7546 2 жыл бұрын

@@marksunghunpark I see! Thank you very much! With this, I can improve my code a bit!

@dev_jeongdaeri 2 жыл бұрын

Async mapper 엄청나네요!! 감사합니다!!👍👍👍👍

@phantuananh2163 2 жыл бұрын

Dope 😍

@codinginflow 2 жыл бұрын

This changes everything!

@RanbirSingh-dl9co 2 жыл бұрын

Above dialogue is said by Bulma from Dragon ball Super when Goku arrive when frizza attacked earth.

@pizzapizzadesu 2 жыл бұрын

great timing. i was just about to make the "mistake 1" one for retrieving images. Really appreciated

@-Kimma- 2 жыл бұрын

This is so good and clear! This also explains some minor issues I have to understand some of the functionality with coroutines. I'm going to use this video as code snippets when coding my coroutines 😀

@skandarsouissi7282 2 ай бұрын

i'm addicted to your videos man, i can't sleep.

@it-6411 2 жыл бұрын

Pay attention, that when you use .awaitAll() function in the list of deferred items and if any of these will throw exception, you'll get exception for the whole operation. So, you should use .awaitAll() only in case, when you except full success of all async calls. In other case to handle exceptions for specific items, you can use list.map { it.await() } and try/catch block.

@PhilippLackner 2 жыл бұрын

Correct, thanks for mentioning :)

@it-6411 2 жыл бұрын

@@PhilippLackner you’re welcome)

@abdremo 2 жыл бұрын

OK🤙

@ChrisAthanas Жыл бұрын

Like this? suspend fun getUserFirstNames(userIds: List): List { // Alternative solution - executed in parallel, but allows for each item to cause exception val firstNames4 = coroutineScope { userIds.map { userId -> async { try { getFirstNameWithExceptions(userId + 1000) } catch (e: Exception) { println("Exception in getUserFirstNames: $e") "Error for id=${userId+1000}: $e" } }.also { } } }.also { }.awaitAll() return firstNames4 } suspend fun getFirstNameWithExceptions(userId: Int): String { delay(500) println("getFirstName: $userId") if (userId > 1005) { // simulate an error throw Exception("userId > 505") } return "John $userId" } // note: I am using the `.also{}` blocks in order to let the IDE show the type at that point in execution

@suleyman_sezer Ай бұрын

thank you for your correctly idea.

@anupdey99 2 жыл бұрын

Excellent content as always! Please make a series about those mistakes. Appreciate your hard work. 🙌

@Shasha-zs4dx Жыл бұрын

Kudos to you for making this video...Learned very tricky points related to coroutines by watching this..Thank you mate.keep making these awesome videos

@adamjacob5482 2 жыл бұрын

Love your videos, love your work. Always great content! Thank you very much :)

@behnawm 2 жыл бұрын

Great stuff Philipp! Keep it up!

@hakimbouatou2558 2 жыл бұрын

Amazing content as always!

@spitze3768 2 жыл бұрын

Great videos! They are very informative and have help me a lot in my shift to kotlin. Keep up to good work!

@jose-naves 2 жыл бұрын

Pure gold. Thanks a lot!

@TiagoDvl 2 жыл бұрын

Really nice model of videos. Keep up, man.

@a.rohimsama7222 5 ай бұрын

Thank you for sharing! super helpful! love it!

@asadnaqvi8901 2 жыл бұрын

The content you are providing is not available on highly paid sites. You are doing great work. Keep it up buddy 🎉🎉

@user-me1ry6lg6d 4 ай бұрын

what an explanation Philip . You earned a like .

@sohaybbahi8983 2 жыл бұрын

Great video, keep on creating great content !

@Ayor88 2 ай бұрын

as always with your videos, very interesting for self learners !

@Lucien-ow5ne Ай бұрын

Great video, thank you!

@imashnake_7151 2 жыл бұрын

Wow you look so much healthier now, great work!

@LogicPhalanx 2 жыл бұрын

Mistake 3 is actually main safe but I get your point. Delay doesn't block the calling thread.

@gaurav7557 2 жыл бұрын

Awesome Man, Thanks a ton for this

@IvanVasheka 2 жыл бұрын

Thanks for the video!

@z-h-d 2 жыл бұрын

nice video to watch before sleep ) easy listening, very clear and positive 👍

@dev_jeongdaeri 2 жыл бұрын

Thanks for super awesome tutorial!!👍👍👍👍❤️

@stanleykou5643 2 жыл бұрын

Excellent examples!

@RexTorres 2 жыл бұрын

Thanks for this awesome video. I learned A LOT. I use coroutines a lot so I will need to review those.

@dedeandres455 2 жыл бұрын

amazing video and good explaination Thanks Philipp

@rahul_spawar 2 жыл бұрын

This video is very helpful , please make more videos like this

@usmallas2 2 жыл бұрын

We need more videos like this one!

@user-us3pn5rt2g 2 жыл бұрын

Can you please, make several hours of such kind examples) so amazing stuff

@cristianovecchi 2 жыл бұрын

Great content, thanks!

@GeolseuDeiGamers 2 жыл бұрын

Thank you so much, your videos are awesome

@otoS97 2 жыл бұрын

Amazing video.I would love more of videos like this. It tests the knowledge and also reminds you details. Really good content.

@shutanovac 2 жыл бұрын

Your best video as far as I'm concerned 👍

@yash1307 2 жыл бұрын

Sir why are you not becoming a Google Developer Expert? Because you provide an amazing and helpful content...

@ssgojekblue 2 жыл бұрын

So true!

@protaties 2 жыл бұрын

*JetBrains Developer Expert

@royce-rich 2 жыл бұрын

Free google sales person = GDE

@anujmukul9284 8 күн бұрын

that doesnt give money!

@MrGfpf 2 жыл бұрын

Great tips! Thanks in advance! Brazil!

@chandlerbing2820 2 жыл бұрын

Love all your videos. Please do more Android studio projects. Thank you so much!!!!!!!

@sergeyplotnikov5031 2 жыл бұрын

Really useful content/ Thank you very much!!!

@datel666 2 жыл бұрын

Nice video! Thanks

@ByronicGuitarist 3 ай бұрын

Great video. Rather than checking if an exception is a CancellationException in a try-catch block, you could use runCatching instead which does not catch CancellationExceptions

@safionweb 2 жыл бұрын

Amazing Content!

@ssgojekblue 2 жыл бұрын

I'm refactoring all my Mistake 5 now 😃

@saquibsiddique2641 2 жыл бұрын

Really very helpful thanks for sharing @Philipp

@PhilippLackner 2 жыл бұрын

Glad it was helpful!

@arash1684 2 жыл бұрын

very useful thanks 👍

@nickolajarjous2639 2 жыл бұрын

Excellent video

@ramasubramanian3154 2 жыл бұрын

please make this a weekly video series.🙏

@solo-ps9vb 2 жыл бұрын

Very helpful. Using coroutines means coding in a new way.

@joaquinalanalvidrezsoto5054 2 жыл бұрын

Sehr tolles Video. You should make more like this :D

@amirhosseinghafoorian9985 2 жыл бұрын

nice issues were mentioned here , especially the defered one

@mustafaammar551 2 жыл бұрын

Thank you Bro

@bjugdbjk 2 жыл бұрын

Even without async just with the launch, we can have parallel execution because both are non-suspending calls !! Async is specifically useful when you want to get something out from a coroutine !!

@thanosfisherman 2 жыл бұрын

Mistake 4. If you make this suspending function return coroutineScope ( The suspend function you also used for mistake 2) or even withContext. Then the cancellation exception will be actually propagated to the outer scopes even if you explicitly catch in inside riskyTask e.g suspend fun riskyTask() = withContext() {}

@antonychepel5797 2 жыл бұрын

Thanks for video! So usefull. What is that IDE? Visual Code or something else?

@thegreatwarrior4989 2 жыл бұрын

Very informative vedio👍👍😉😉😉

@HosseinKurd Жыл бұрын

Amazing and useful

@PhilippLackner Жыл бұрын

Thanks a lot

@TheKuoala 9 ай бұрын

One thing worth mentioning for Mistake1 is the fact that coroutineScope will suspend until all the async calls finish. Therefore reading the result code like this could be confusing since you aren't really waiting for anything outside of the coroutineScope block.

@amnsatija 2 жыл бұрын

best corotuines video ever

@otoS97 2 жыл бұрын

Everyone is providing video ideas so I would say it too: Running android Junit and Android tests on Gitlab's CI on every commit. If you're had any experience with this it would be a great video. Maybe with docker maybe without it.

@jpvs0101 2 жыл бұрын

Thanks for saved me from Mistake 5

@christianmeazza2309 2 жыл бұрын

I'm glad you're here to tell me about those mistakes, you are the best. I see the next video coming: "5 Fatal Kotlin Flows Mistakes Nobody Tells You About" :D

@dk6024 2 жыл бұрын

In the first example, you could have mapped over the incoming IDs and avoided some code and mutability.

@purplehazer417 2 жыл бұрын

Hello from Poland:)

@ChrisAthanas Жыл бұрын

@PhilippLackner @17:36 you mention needing to cancel the long-living CoroutineScope, but did you mean any Jobs that were started with the long-living CoroutineScope, and not cancelling the CoroutineScope itself? I dont see any way to cancel the CoroutineScope, just jobs associated with the scope. Please advise.

@alishanvaliani9952 2 жыл бұрын

Hi! Make video about Maps Compose, Please!

@user-ew8wc2mc1o Ай бұрын

Hello, thanks for the amazing videos but one question always concerns me: isn't sometimes the overhead of creating a lot of coroutines defies the purpose of performing tasks in parallel? or wouldn't it be a problem?

@AdrianTache 2 жыл бұрын

I think mistake 2 is misleading, because that code should be safe as written. But I agree, with components that aren't coroutine safe, like long running calculations, you should do a check before continuing them whenever it makes sense.

@johnf419 2 жыл бұрын

Agreed, I think the example was not realistic

@kemasdimas 2 жыл бұрын

Wow thank you, didn't realize I made a lot of inefficient coroutine calls in my app! 😅 Does your paid course cover this extensively? Will need to check it out

@PhilippLackner 2 жыл бұрын

My paid courses cover lots of topics and best practices in a bigger practical project 😄

@kemasdimas 2 жыл бұрын

@@PhilippLackner bought it, thanks!

@l_a_h797 6 ай бұрын

Very helpful explanations! At 4:07, with what keystrokes did you move the whole for loop up together? Ah, looks like Shift+Cmd+Up on Mac. Very useful! (Unfortunately, the video title is misleading clickbait. These are not mistakes that "nobody tells you about." Making your suspend functions main-safe, for example, is a principle thoroughly discussed in Android documentation about coroutines.) On mistake #5, the point is valid that the lifecycleScope is too short-lived for the purpose of posting data to an API, and using the viewModelScope is an improvement. But the ViewModel too can be destroyed (for example if the user navigates to another activity) while data is being posted to the API, and that is not what the user wants either. Android docs recommend that "business-oriented operations," such as uploading users' data, should survive even process death. For that, WorkManager is recommended.

@ivanstefanenko438 2 жыл бұрын

Thanks for the videos, they are really awesome! One question about Mistake 2: what did you mean when said we will stay in while loop if will not check for is job active? Did you mean while loop will continue executing even after we cancel job? Probably I've caught smth wrong, so will appreciate it if you clarify this thing!

@PhilippLackner 2 жыл бұрын

Yes it will go on after canceling

@DanieleSegato 2 жыл бұрын

That code is long running and has no suspended calls in the middle, it's regular code. Meaning it's your job to check. If you had the same loop with a suspending function to create a random you wouldn't need to check cause it would be checked automatically at the next suspending call.

@GakisStylianos 2 жыл бұрын

@@DanieleSegato actually having a suspend function doesn't automatically fix this. If that suspend function doesn't also cooperate with cancelation then it will still keep going on forever. All suspending functions inside kotlinx.coroutines do cooperate with cancellation but that may not be true for your own suspending functions!

@ivanstefanenko438 2 жыл бұрын

Roger that! Thank you all for the answears!

@zekininadresi Жыл бұрын

I think using launch would be better as async would bring all parent the scope down if once job fails to retrieve the name (unless it's supervised).

@s-w 2 жыл бұрын

I see a Philipp Lackner video, I click.

@zanyking 2 жыл бұрын

Be careful while using async in web backend development, if the function is going to be triggered by client request, and you expect high QPS on this function, then you have to create your own thread pool for this async to use Never use default thread pool, because it’s small and might exhausted and cause other client requests await

@Nekrull 2 жыл бұрын

You're right that suspend functions should not be exposed to the UI and I'm with you 200%, but have you seen Google's paging library? that thing not only uses suspend functions to submit data to the adapters, but it also seems to run load queries on the UI by passing the paging source to the list's adapter, it's actually the only library that I promised that I will never use

@PhilippLackner 2 жыл бұрын

I don't like the paging library either, but the load queries are done in the viewmodel afaik

@Nekrull 2 жыл бұрын

@@PhilippLackner I will test it out but I don't think it does it on the view model, you post a paging source (which in effect is an object that contains suspending functions to load the data) to your paging adapter through the fragment or activity's lifecycle scope, so it's pretty much impossible to run something on viewmodelscope, though I guess you could create the adapter on viewmodel and let the observer attach it to the paged list, but adapters in the view model are a bitch to unit test without robolectric

@Monarch_943 2 жыл бұрын

Damn this was a very good video! it seems I'v been making alot of mistakes :/

@PhilippLackner 2 жыл бұрын

Time to stop making them😁

@crayolaksh 2 жыл бұрын

Hi, mistake 2 can also be handled with a withTimeout block right? it'll throw an exception if the operation within takes longer than specified time. Please correct if I'm wrong

@psistarpsi80 2 жыл бұрын

I wish you'd make a video like this for Lua. Lua coroutines continuously befuddled me.

@StreetsOfBoston 2 жыл бұрын

Nice video! But Mistake #3 is not a mistake at all: The function "networkCall" *suspends* for 3 seconds. It does not *block* for 3 seconds. Since "networkCall" is not blocking, there is no need to fix it by using a "withContext". If you wrote/coded "Thread.sleep(3000L)" instead, then this example would have been a real mistake, since you could have *blocked* (not suspended) the main thread.

@etiennebeaulac8148 2 жыл бұрын

The issue is not that he thought it was blocking, but that the function was not main-safe, which is a mistake. Changing the context to Dispatchers.IO was the right thing to do. Of course, as he mentions, if you use Retrofit you don't need to worry about this since it does it for you.

@StreetsOfBoston 2 жыл бұрын

@@etiennebeaulac8148 If the "networkCall()"'s body contained "Thread.sleep(3000L)" (or has some actual blocking call like waiting for a socket), then switching the context to Dispatchers.IO would have made perfect sense Written as it is, the code in Mistake -#3, is entirely main safe, since there is no blocking code, only suspending code. Replacing 'delay' with 'Thread.sleep' will make it blocking and not main-safe. It's a bit of nit-picking, but I think details are important sometimes 🙂

@danyelsh874 2 жыл бұрын

Awesome

@7xFuryPlayz Жыл бұрын

my question is ? will its good or bad to use repository class in the last mistake ? i think so viewModel should not interact with your api , repository class should interact with your api and give data to viewModel and then viewModel give data to activity or fragment ui right ???

@path_ethics 2 жыл бұрын

How to create and manage cancelation of our own scope, for example in case we want to have a scope binded to our whole application?

@LouisCognault 2 жыл бұрын

Your solution to mistake #2 still has a mistake: If cancellation happens while delay is suspended, job will never be cancelled.

@DanieleSegato 2 жыл бұрын

True

@aleksandr.liublinskii 2 ай бұрын

In mistake #1 since we have multiple coroutines spawned by async, and they all access the mutableListOf concurrently, shouldn’t we use thread safe data structure, for example COW list instead?

@zeyadabdo1964 Жыл бұрын

Do I need to call suspend functions of Retrofit and Room on a background thread?

@grimonce 2 жыл бұрын

There's something weird with the first example... isn't appending to the list synchronous in here? Why didn't we include it in the async block? I don't know the first thing about Kotlin, I use different tools, but to me this didn't fix anything, unless using "coroutineScope" makes appending asynchronous somehow... Also won't adding the firstNames to the async block become a race condition? Is the memory reserved for the result ahead of time thanks to the type DeferredString?

@ackerman6992 2 жыл бұрын

Why it necessary to call async function inside coroutine scope? 🤔 We can call a suspend function in other suspend function right? Or we call coroutine scope so that the function inside coroutine scope works independently?

@skullkrum20 2 жыл бұрын

Usually your coroutines code runs sequentially. We use async so that we can immediately loop and call async again for the new iteration. This way you start all jobs initially and then wait for all of them to finish with "awaitAll".

@ackerman6992 2 жыл бұрын

@@skullkrum20 yes i undestood that, but i was asking why we need to call async inside coroutine scope.

@skullkrum20 2 жыл бұрын

@@ackerman6992 Its for that reason. If you don't you will run everything sequentially. Usually you don't need to if you're fine with that. Good name btw, I'm in love by Shingeki no Kyogin. :D

@ackerman6992 2 жыл бұрын

@@skullkrum20 ohk got it, Thanks 😂

@bjugdbjk 2 жыл бұрын

@@ackerman6992 coroutinescope, in this context , this is required because u r launching the coroutines with async, and to control them u need coroutinescope here !! And inside a suspend function we can't launch a coroutine !!

@silvestreramirez4515 2 жыл бұрын

But for example if I have one thousand client IDs this works? Can I have one thousand async task at the same time running?

@GrahamFirst Жыл бұрын

In mistake 3, shouldn't "networkCall" just return a string (or throw an exception)? I don't see the point of wrapping it in a Result in this case.

@aherbel 2 жыл бұрын

For Mistake #1, doesn't creating a new coroutineScope inside a suspend function loose the parent scope? I mean, if some error is thrown inside that coroutineScope, the parent will not get cancelled...

@bobbybeat1 2 жыл бұрын

The coroutineScope function creates a CoroutineScope that inherits the context of the parent and forwards cancellations/exceptions to the parent scope. More info: kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/coroutine-scope.html

@_checkit Жыл бұрын

#5 so let's say that button is a "save and close" button for the current activity. What then? You pass the "finish()" method as callback to the viewmodel method?

@edwinkungu1155 2 жыл бұрын

Waiting for the day you'll call it co-routine

@codingwithsam4992 2 жыл бұрын

Hey Phillip, Its Samuel Laskar again. Can you please share some ways to make money by developing android apps. As playstore is already very saturated and freelance sites pay very less

@PhilippLackner 2 жыл бұрын

I'll soon upload such a video, yes

@jatinvashisht4293 2 жыл бұрын

@@PhilippLackner patiently waiting for it :)

@maskedredstonerproz 2 жыл бұрын

I would imagine use a different store, either that or make courses

@deepeshkumar1704 2 ай бұрын

Can i update UI like async(first) method?

@rustamibrahimli2113 2 жыл бұрын

Can you tell me please: What is your Color theme? This is such a beautiful theme

@bjugdbjk 2 жыл бұрын

shld be Xcode-dark

@DanieleSegato 2 жыл бұрын

Randomly being suggested your video, decide to watch it. Well the 4th mistake, you are partially wrong there with your explanation: if you throw a cancellation exception in your code, yes, you would eat that up. But in most cases the cancellation exception you would be catching would be from a suspendable function, your delay in this case. And what would happen there is that the coroutines would have been calcelled, regardless of you catching the exception or not. BUT if you cancel the exception and then try to execute some more suspendable call after that it would fail. So your solution is correct, you should be doing that (checking for cancellation / avoid catching cancellation exception. But your explanation is not entirely correct. :-) hope I was helpful