Background Tasks Are Finally Fixed in .NET 8
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- čas přidán 20. 08. 2023
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Hello, everybody, I'm Nick, and in this video, I will show you how Background Tasks, Background Services or Hosted Services have changed in .NET 8. The changed in .NET 8 ultimately fix a lot of the complaints we had in previous versions.
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#csharp #dotnet
Classic 'hellœverybody' always brightens my day
"euhlihstyocontent" if you add up all the time nick saves on not pronuncing consonants in his intros it'll be thousands of years. Time he generously puts towards giving us the best dotnet content in the world.
@@yearlyoatmealI actually don't know what that part is 😂
@@EricPhillips89 it's "if you like this type of content" :)
he explained in a comment a while back that the reason he speaks so fast has to do with viewer retention. In my humble opinion he would win by speaking a bit slower and clearer and then speeding the whole thing up afterwards. But I'm grateful for the great content anyways
Also: “I’m Nick and in this video…” becomes “I’m naked in this video” 😂
OOOHHhh man if this new feature was released a few weeks earlier it would have saved me a lot of time. I had the exact same problem with worker-services management and had to come up with a custom solution. After this video I will update my project to .Net 8 :)
This video seems to be made especially for me, thanks for everything. You are the best!
I implemented my own version of IHostedLifecycleService with exactly the same functionality for my pet project. I had a bunch of background processes sitting side by side and posting stuff to the shared in-memory message bus. Discord bot, Twitch chat bot, Twitch API polling, database storage abstraction, and REST API to manage all that. All have to start concurrently, and all have to be aware of the whole lifecycle of the application (starting, started, stopping, stopped), so they don't message into the void and clean stuff up properly. And I build the first PoC for .NET Core 2 which is now as old as a first-grader, haha
i did use background service for many things and usually with the new timer which i found out about on this channel, thanks
Very nice explaination. I'm actually developping a service right now that can used this feature. I'll be looking forward to implementing them in the future.
Adding 'await Task.Yield' as the first statement will also prevent the background service from blocking
I came here to say exactly the same thing! I've been doing that since day one with them!
@@f135tathat wont really fix it. The host still awaits the StartAsync task. With Task.Yield, you just giving some other task in the queue to have a chance to do its work. Which is silly because at the time your StartAsync is called (assuming it is the first one), there is should be no other task in the TaskScheduler. And (without this new option) another StartAsync wont be called if the one before it has not yout completed.
Outside the while loop?
@@natan_amorim_moraesyes
Thank you Nick. Great explanation! I think BeforeStart, Start and AfterStart would be less confusing.
I guess that naming is a Microsoft thing.
@@nitrovent sure. I have no complaint against Nick 😀
@@Kingside88Well I didn't think so ;) Just wanted to emphasize Microsoft being Microsoft. I know >10 years old SharePoint code uses that naming convention e.g. in their feature receivers...
Thank you Nick, this was so insightful
I think we should also have a per-service boolean that indicates whether the service can start in parallel or not. You might have multiple background/hosted services, and some of them might need to start before the application starts, while others might not care as much
When to use channels in C#?
Channels in C# are designed based on the single-producer, single-consumer (SPSC) pattern. They provide a reliable and efficient way to pass messages between producers and consumers in a concurrent system. The design of Channels in C# is optimized for scenarios where a single consumer processes the messages.18 May 2023
If you know, you know.
I would prefer having 2 separate class named "BlockingBackgroundService" and "NoBlockingBackgroundService"
I agree - this breaks anywhere where you are doing things such as migrations on app startup. The fact that IHostedServices ran in the order that they are registered makes them perfect for ensuring something is executing before the app framework launches. For example, MartenDb changed Db initialisation into an IHostedService in their latest version. Many libs handle it this way. I'd say there needs to be a separate interface which filters certain registrations to run in the previous format, and have the rest covered by IHostedService. Perhaps IStartupService? Technically these absolute run fifo services that we still need dont usually persist as background services for the lifespan of the app, once the task is finished, thats it - they are done. I always felt IHostedService was a bit misleading for those. This is purely unless all 'starting' tasks on the lifecycle service are guaranteed to run before any 'start' tasks, even if executed concurrently. If that is the case, then the new interface is exactly what we need
@@georgepagotelis Channels aren't necessarily single producer nor consumer. You can have multiple of either. The only restriction they have is that a message may only consumed once. Also, they're not as good as Golang's channels since they don't allow capacities of 0 (aka producer-consumer synchronization).
@@parlor3115channel.Reader.TryPeek() doesn’t consume the head message
If you look at the implementation of the BackgroundService class you will see how starting with Yield or Delay will make it non-blocking for other services starting. I am always amazed that most programmers don't get that the first part of the async method executed in the time slice of the caller. Until it yields. Using Task to start off async work is thus tricky and that is where the blocking issue originates.
Do you know any clearly explained tutorials about this? I'm really struggling to understand yield etc
Excelent stuff coming up in .NET 8, thanks for the update Nick! Great video!
Never had this issue. But i usually startup immediately and cache stuff later vs heavy startup.
We use background services for db migrstions and to keep observables for signal R or other reactive tasks.
Yup, introducing new hooks is a big thing if there is need to do some async work on app closing for example. Great sharing, Nick!
Why can't you do them in StopAsync?
@@parlor3115 I think you can also do it after app.RunAsync stops.
antipattern really and it will not work for some long pending async jobs and you have to watch out for cancellation tokens so fighting the framework feels like not a very good idea
Simple reason to use a 'blocking' hosted service: DB migrations. Your migration might take a bit of time. Don't want the web app to start accepting connections when the migration hasn't completed - could mean your code would error because the DB is not in the correct state.
Background hosted service not blocking are also great for other things, instead of having to use hangfire or Azure Functions etc. (keep them light weight though, peeps. might need to consider scaling out, etc).
Migrations don't really belong on the start, but on the deployment pipeline... at least that's what I do.
Or you could trigger your migrations from an IHost extension, giving you access to application services and blocking the app start as intended. I have never felt the need to block the start of a hosted service and if I did something that blocks, I would fire another Task anyway to do the work.
Then run your migrations as part of your application startup pipeline. A bg service should run in the bg...
@@mAcCoLo666 If your app has the right to run DDL scripts your security is compromised. The db user that your app uses should have r/, or r/w access at the most and execute if you're calling stored procedures.
Excellent content! I searched here but I couldn't find the explanatory video about the differences between Background Services and HostedService, could you give me the link please?
I think the only way to rationalise the names is that they used start and stop already and needed a name for an event before start and stop, and starting and stopping was the best they could come up with
thanks for your amazing videos. i have a question : could we use background service to launch it at the stating of the project and use it to store some configuration in for example: a json file for the first time we launch the whole project ? and what is the best scenario for this situation ? thank you
I used an azure function as my background service. But involves passing a message from one system to another.😊
I just wrote a service yesterday injected into a background service to assist with blocking my applications startup. Can’t wait to upgrade and delete everything 🎉
This is one "fix" I wish they didn't make. There is a very good reason that BackgroundService is written the way it is and I do not agree that using the currently provided methods for background work are broken at all. Now a single host-wide setting might have unintended consequences when using 3rd party libraries.
Brainlessly using 3rd party libs without Reading docs, or using bad ones that have no docs always had some sort of consequence
My exact sentiment. We have written libraries with a very good reason to have one IHostedService.StartAsync not start before another has. Now, some ignorant dev is going to enable this new option for (maybe a legitimate reason for one usecase) and potentially causing a trainsmash with other IHostedService implementations. If anything, they should have made this an option per implementation.
so... where do you put the work in the second example? The IHosted(LifeCycle)Service? Do you create a timer manually to periodically do stuff?
I was just using these in my app and i was wondering "how did i miss this video?!" only to realize it was uploaded 14 minutes ago lol
We use background/hosted services a lot. Typically we solve the blocking nature of them by starting worker task in startasync, storing task in private member and cancelling it in stopasync.
i'm just curious. using a bg service, how do you prevent iis from recycling/stopping the bg service?. i've tried miriads of configurations options but at not avail. we basically need the bg service to be up and running even the page doesn't get used.
@@fopsdev3676 we don't really use iis, httpsys on windows and kestrel on linux. Hosted services are mostly used in backend webapi-s. We didn't have any issues like you described.
Just as everyone else does... This is not a fix.
@@KieranFoot I didn't say it's a fix. It's a solution that works. I think there is no need to fix anything. Sometimes you need to block the start of the service sometimes you don't and there is always a way. And you can create small simple abstraction layer, extract it into library and re-use it across all your services. The only problem is that not everyone is aware of current behavior.
@@fopsdev3676 Background services only get stopped if the application stops or you call the StopAsync from another part of your code. If you are using timers or tasks on StartAsync you have to store them in a field in order for them to not be disposed. Backgronud services have nothing to do with pages.
Good info. just FYI though, the audio sounded very weird today.
Be useful to have a real world example showing which method you should actually do the background work in and to show how Starting, Start, Started etc should be used
Can you create and remove background jobs programmatically like hangfire ?
Still missing feature is what to do if I wanted some of the services to start concurrently and some in strict order?
Yep, the same thing came to my mind. I want to be able to configure on a service level whether I care if it's synchronously executed or not
good job 🙂🙂🙂🙂
It's a great video, but it is a bad practice to put that kind of code (calls that might take a while to complete) in the startAsync. Just move all that code to the ExecuteAsync method.
I still cannot understand why dotnet team didn't introduce something OOB for running anonymous background tasks via background job and default queue channel for it. Like some service where I can put my Task, get tracking Id for it and just to be sure that it will be executed eventually (something similar to what Hangfire do, event it's just in memory queue). It is strange that I need to implement custom service for which individual peace of domain logic, taking into account that it could be done in domain-agnostic way easily
Let me see if I understand correctly: the new interface IHostedLifecycleService should be used when you need to execute something once at application start (or stop), and the BackgroundService should still be used for tasks like periodically polling a queue?
Thats how I picked it up as well. I know I have seens IHostedServices that just spin up a long running background Task in the StartAsync to get something like the BackgroundService. I have lso thought that that (how we picked it up) is not actually how it is ment to be used.
That’s how BackgroundService implements it.
Thank you. I was developing my kludge workaround when I found your tutorial. I also would like to fail the whole service if some of the background services didn't went live/recovered after some time. For example, during lost connection.
Actually, your example didn't help me. The whole service froze
What would be the best way to execute a background service on a schedule now? I think I remember you have a video about this in the past, but what is best now with .net 8 and these improvements? Say, like, I want to execute a job every hour, or at 01:00 AM every day.
Doesn't seem like there are any improvements on that front, so your best option is still manually using PeriodicTimer in a BackgroundService.
Google "Run and manage periodic background tasks in ASP NET Core 6" for a pretty good article on that.
Way I do it is similar to what’s discussed here in the ExecuteAsync method await some Task.Delay(TimeSpan). To get the timespab you need there is a great library called Quartz that effectively parses Cron schedules. You can get the time delta from now -> next cron schedule execution and await that in the Task.Delay
Hangfire comes to mind
I have question here about this background service ,once we deploy the web app to IIS the background service would not work until a request coming from any client! ,otherwise it will not started
how could i fix this ?
Hi..
Are these background services and hosted services still seen as singleton?
Reason for the question of course revolves around running EF Core databases or scoped dependency injections that would still require using / creating the service scope, unless you bring the DBContext in as singleton, which is highly frowned upon..
You can inject a DbContextFactory as Singleton, then create the DbContext when you need it. (And dispose of it quickly). This is better than having to inject IServiceProvider . For Service that don't have such a factory alternative, I'm afraid injecting IServiceProvider is the way to go.
@@hyperpaus- Thanks.. that's exactly what I am doing at the moment - creating a db scope from the DBContextFactory when i need to get information out of the DB..
I am, however, exploring one level up now - aka creating scope in the singleton wrapper class for a scoped class and dependency injecting the DBContext into the scoped class..
I will feedback once working.. 😉
This is /exactly/ what I need right now lol. I have a particular service that depends on a rediculous Google Calendar API query (like upwards of 40seconds retrieval time); but once that data is retrieved, it isn't likely to change very often. So I have a service that Caches that query result and periodically checks for changes while the end users get fast results from the cached data. This will make that service so much cleaner.
Hi Nick, Unable to call the external WCF by adding the URL as service reference in the C# lambda function . can you please help me on this . when I am adding as a service reference its not recognizing the service client and method contracts .
Im trying to fix my issue where if it takes a little too long to shutdown and you had used the restart service to restart it - it will fail restarting because it exceeds the timeout.
Does this change anything (except for IHostedLifeCycleService interface) for Worker Service project with multiple Background Service ? Basically does ServiceStartConcurrently has any impact ? It isn't available in WorkerService project.
I wish I had the ability to stop and start and add and remove hosted background services myself at runtime.
Is Solution Architecture something like CQRS which you only need when you develop on really large applications? So I probably wont ever need it?
The annoying problem in these services is scaling. When you run multiple pods with your app, and each of them running their own background services, when what you really need is only one. (Like db interaction, external api call, etc).
You missed one important topic. Communication between the background/hosted service and the main thread but brillant otherwise.
In the background .NET just puts all hosted services into group of tasks and does await Task.WhenAll(). So the difference with the prevoius approach is that several hosted services start concurrently between themselves as opposed to being started one after another in order of registration, not that the application now starts concurrently with the background services. So, I'm not sure that your statement at 7:29 is accurate.
What is the purpose of having a Starting and Stopping handlers? This was not clear. Aren't the Start/Stop handlers sufficient?
Timezone is always wrong. What can i do to fix it?
4 or 5 hours of differences
Imagine you have one background service that creates a request every minute to some third party API. Now also imagine if you have multiple instances of your webapp running. Does this mean that every instance will make a request every minute? How would you limit execution of a background service to one instance?
I've used Background Services in the past, but still prefer a good old C# console application that is cyclically ran by the Windows Task Scheduler. In my 20+ years of experiences this beats every other technology, including Windows Services.
Will work great in Linux Docker. 🙃
@@Benke01 Honestly, I do not know, as I'm nearly using Docker close to never. I would assume that it also could run just as well as a cronjob?
Windows Services have a different use case. It's not a substitute for scheduling tasks, although you can use them that way.
@@UweKeim As it is now it will be platform independent and you can easily use it in the cloud or just spin it up locally without having to do any Windows service setup. A cronjob however run on a timed schedule. You can mimic that with a background service but less conveniently.
This also naturally fits into distributed/microservice architecture. I can have multiple chat bots, DB abstractions, and a REST API in one executable to run on my gaming PC, but putting them into separate Docker containers gives me way more control and flexibility.
For many years, JAVA ruled the business software world due to its ability to run on multiple platforms including Linux (which allows it to run in containers).
Ever since .NET core came out, however, that advantage was erased. When you combine this fact with the .NET framework & the incredible advancements to the C# language, I can't see why anyone would choose JAVA over .NET today. Thanks for another great video.
Will this be functional in Maui?
Ok now tell me: why couldn’t they add the new interface methods on the IHostedServices interface and have a noop for those extra methods?
Adding them to the interface would force everyone who has implemented that interface to update their code to include the new members, and would break if you tried to run anything that was compiled against the older interface on the newer one.
@@SytheZN...unless they added default implementations for them.
However I think it's still would be an overkill to have 6 methods on simple IHostedService interface, now it's easy Start and Stop, more complex cases are quire rare anyway
Is Hangfire still a good choice to manage background tasks in 2023?
Yes. It has its place. But Hangfire an IHostedService is not in the same category. IHostedService is tied to the lifetime of a hosted service. Hangfire runs tasks on a schedule.
No more yielding that long startup task!
You should've passed your cancellation token to your Task.Delay()
It's features like these that make me want to migrate from framework
... doubt it...
update ur ride man :D
And how is dbcontext running now? Does it still need Scope Factory?
Hellovrybody
I use Coravel for Queues
protected override async Task ExecuteAsync(CancellationToken stoppingToken) {
*await Task.Yield();*
^-- blocking nature does NOT exist if you you yield control back to the minimal api (app whatever) you're running while your backgroundhost service takes "20 seconds". No need for that fancy code.
Microsoft need to fix two things, when published it "automatically" kicks off instead of having to hit the URL endpoint and application lifetime starting/stopping (i'm hoping has been fixed cause it's a little weird knowing if deployment or it's crashed etc).
Don't do it at all. Post a message to a queue and expose and API instead.
Sometimes a queue is too much of a pain for simple tasks.
Nick The Greek....
Microsoft? You mean .Net foundation ;P
Such a long jorney for MS to make a clean code... And this is not a rocket science after all
Just an FYI, every time I see the words finally, insane, genius ect.. I go out of my way to NOT watch the video, even if it's from a content provider I am subscribed to. If it happens enough, I end up unsubscribing.
Thank god I'm not using c# anymore
Why not ?
What are you using instead?
What is the name of video about Hosted Service on this chanel? I can't find it @nickchapsas
Welcome back to the Global.asax
Adding 'await Task.Yield' as the first statement will also prevent the background service from blocking
How does it manage that?
@@Mark-px3rq Yield will return from the Task and continue in the background.
But why waiting synchronously on a bg service? Especially seen as you can make it await.
configureAwait does not fix this, does it? it is obvious that “await” by default is running in the same thread.
@@justengineering1008 No it doesn't. That's why I didn't mention configureawait ;-)