Guidelines for creating a background server?

Question

Guidelines for creating a background server?

J. Diego Rodríguez Royo 6

I'm developing an App that communicates with a remote server using a web socket, currently, it only opens the connection when the app is open in the foreground. I'm trying to search how can I create a background process that keeps the connection open to handle messages from the remote server.

I also would like the background process to be started at log-in, after an update, and if the process is closed, open it again when the App is open.

I've already tried to do this using exe arguments that avoids opening the whole app and it only opens the connection and then I set the thread to sleep indefinitely with Thread.Sleep(Timeout.Infinite). It works, but I don't know how can it be opened in the different cases I mentioned above. I've been thinking to use windows.startupTask extension, but I don't find a way to configure two of them (One should be for the app and the other for the background process and should be managed independently, so that the user can allow to open the background process at log-in, but not the App). I also tried to open the background process from the App with FullTrustProcessLauncher.LaunchFullTrustProcessForCurrentAppAsync("Arg1 Arg2") when RuntimeHelper.IsMSIX is set to true but although the method is called, nothing happens.

Maybe there are better approaches than the mentioned way, maybe ComServers... I don't know, I'm pretty new on background process in Windows App SDK.

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Answer 1

Xiaopo Yang - MSFT 12,736 Microsoft External Staff

Hello @J. Diego Rodríguez Royo,

You can Create and register an out-of-process background task in WinUI3, an example, Or Create and register a Win32 COM background task.

Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2023-08-22T07:18:07.7566667+00:00

Tested the sample which Creates and registers an out-of-process background task and it works fine. Another important point is to

Find out whether the background task is already registered by iterating through the BackgroundTaskRegistration.AllTasks property. This step is important; if your app doesn't check for existing background task registrations, it could easily register the task multiple times, causing issues with performance and maxing out the task's available CPU time before work can complete.
J. Diego Rodríguez Royo 6 Reputation points

2023-08-22T07:26:08.7166667+00:00
Hello @Xiaopo Yang - MSFT
Thanks for your answers.
Because the background task will be open indefinitely, I will need to set at the appxmanfiest the following capability:

<rescap:Capability Name="extendedBackgroundTaskTime"/>

But then to avoid opening multiple and unnecessary connections, how can my app know if the background task is already running.
Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2023-08-22T07:38:26.06+00:00

Does BackgroundTaskDeferral work for you? As far as I'm concerned, you can define class fields to avoid opening multiple and unnecessary connections.
J. Diego Rodríguez Royo 6 Reputation points

2023-08-22T08:19:11.1133333+00:00

I don't know how BackgroundTaskDeferral can help. Does GetDeferral() block the thread if there is another task with the same deferral?

I don't know neither how class fields can avoid that, I mean, I can create a boolean field that is set to true the first time is run, but then I don't know how other instances can get that info.

I also remembered about AppInstance class and maybe AppInstance.FindOrRegisterForKey method and AppInstance.IsCurrent attribute can do the work (see Making the app single-instanced (Part 3) - Windows Blogs).

EDIT: I tried AppInstance in the background task, but it looks like that AppInstance.GetInstances cannot retrieve background task's instance from the main app.
Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2023-08-23T01:07:00.66+00:00

It's by design for AppInstance::GetInstances().

Windows App SDK: GetInstances returns all running instances of the app that are using the AppInstance API, ......

See https://learn.microsoft.com/en-us/windows/apps/windows-app-sdk/applifecycle/applifecycle-instancing#list-of-instances.

To communicate between out-of-process background tasks(processes), see Interprocess Communications. For example, File Mapping.
J. Diego Rodríguez Royo 6 Reputation points

2023-08-23T10:57:51.47+00:00

I've been searching information and examples for File Mapping Interprocess Communication, but there isn't many examples. I ended asking at Bing Chat and as far as I understand, it consist on writing data on a file on the disk, right?
I don't really think that this way will work, because if the process is closed suddenly, next process that try to open the connection will find that the file "says" that there is already a process with a connection open...

I have tried an Windows App SDK sample project that contains a Widget that works with a ComServer, and AppInstance seems to work and I can get the widget instance from the main app, I was going to try to create my own ComServer in my app following the guide you provided, but there are some parts that doesn't work.

Could you provide me a Windows App SDK ComServer example?
Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2023-08-24T01:01:01.52+00:00

WindowsAPPSDK Notifications also involve in <com:Extension Category="windows.comServer">. App notifications, Push notifications, the difference between WindowsAPPSDK and UWP.

Also see BackgroundTaskWinMainComSample(C#).
Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2023-08-25T06:09:17.7733333+00:00

Hello @J. Diego Rodríguez Royo, any update?
J. Diego Rodríguez Royo 6 Reputation points

2023-08-25T06:14:30.9+00:00

I'm really sorry @Xiaopo Yang - MSFT
I could not test it because I didn't have time, I will give a try today and during the weekend
J. Diego Rodríguez Royo 6 Reputation points

2023-08-25T10:34:23.9233333+00:00
I've been testing BackgroundTaskWinMainComSample, and it looks that the background task doesn't work. I compiled and launched the app in to register the background task to then be able to trigger the app from life cycle events at visual studio, but nothing is launched. I went into the Event Viewer, Applications and Services Log > Microsoft > Windows > BackgroundTaskInfrastructure > Operational and there I saw the following events about the app:

Background task with entry point {087dc07b-fda5-4c01-8bb7-18863c3ee597} named TimeTriggeredTask could nots be started; Error code: 0x80070003

(The log was translated from Spanish, so maybe there are some inaccuracies)

So it looks like that the trigger works, but nothing else.
J. Diego Rodríguez Royo 6 Reputation points

2023-08-28T17:21:27+00:00

Hello @Xiaopo Yang - MSFT , any news about the issue?
Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2023-08-29T01:13:14.7466667+00:00

@J. Diego Rodríguez Royo, Creating and registering an out-of-process background task is a workable way. There is no more document about how to register a Win32 COM background task in WinUI3. You can create another thread about the issue and complete the thread. Thank you!
J. Diego Rodríguez Royo 6 Reputation points

2023-08-30T19:32:47.34+00:00

Hello @Xiaopo Yang - MSFT
I finally managed to get a COM background task that uses time trigger and it is run only once thanks to some COM helpers I had related to the widget COM Server.
Now we can continue to the next part of the question:

I also would like the background process to be started at log-in, after an update, and if the process is closed, open it again when the App is open.

Any idea?
Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2023-08-31T01:55:56.0566667+00:00

log-in: There are SessionConnected SystemTriggerType and SessionConnected SystemConditionType.

after an update: ServicingComplete or Run a background task when your UWP app is updated

open: Trigger a background task from within your app
J. Diego Rodríguez Royo 6 Reputation points

2023-08-31T06:26:51.2033333+00:00

Awesome! Thank you a lot :) I will try them later.
I have a question with after update task, how do I declare an update task based on a COM background task? Specifically the Entrypoint property, should I set the COM Background task GUID as Entrypoint?
J. Diego Rodríguez Royo 6 Reputation points

2023-08-31T15:12:50.67+00:00

I've tried SystemTrigger and AppTrigger, but both throws the following exception when calling BackgroundTaskBuilder.Register(): System.Runtime.InteropServices.COMException: "Incompatible request (0x80070032)"
Xiaopo Yang - MSFT 12,736 Reputation points Microsoft External Staff

2023-09-01T05:26:44.16+00:00

There could be some potential limitations about WinUI3 COM background tasks. but there is no WinUI3 document to follow. Can you create a new thread with a minimal sample about the issue and complete the thread?

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Guidelines for creating a background server?

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