Qt service with gui

franco.amato

I need my application to not be closed by a user who does not have administrative rights and I thought, therefore, of transforming it into a Windows service using the QtService located here: [https://skycoder42.github.io/QtService/index.html]
I know that a Windows service usually doesn't have a GUI and I'm not sure it can have one. Unfortunately In my application I have to display the webcam content in a QtWidget and so I need a Gui. I'm wondering if the Windows service is the correct solution to solve my need and if it is, is it possible to show a gui?

Pl45m4

@franco-amato

Just a thought:
Most Anti-Virus Software is also running as a system service on Windows, so some unprivileged malware running under the same user can't stop the AntiVirus before it's being detected.
They also have a GUI, but the background (detection) service is probably another process compared to the User GUI.

franco.amato

Can I have a help with the global design?

JonB

@franco-amato
Cannot imagine what your use case is. But a Windows Service cannot normally have a UI. Rather than my guessing whether any of them work, you might Google for windows service with ui and have a look through the various questions/answers. I am not sure any of them will work, at least nowadays.

artwaw

@franco-amato Usually design goes like this:
you have one process running as a service, with privileges. The other one is with GUI and what not, doing actual work.
While I am not sure how one can prevent gui process from being closed, the work of a service in this case would be to monitor/being notified about the closure and if that's the case, respawn the gui and possibly notify some API that the incident happened.

JonB

@artwaw said in Qt service with gui:

respawn the gui

I think that will be "tricky" from a service. For example, it doesn't have access to the desktop and it doesn't run as the desktop/logged on user.

franco.amato

@JonB T Don't you think that I already performed a google search before posting here?

JonB

@franco-amato
Not particularly, no. A lot of posters here don't, in fact probably most. And if they do they usually say so and what they came across. You asked if it is possible to show a GUI from a Windows service, and I suggested it is not, so far as I know.

artwaw

@JonB said in Qt service with gui:

it doesn't have access to the desktop and it doesn't run as the desktop/logged on user.

Yeah BUT :) I assumed gui runs as an identifiable process, at least that's what I think OP implied here. You can monitor that from the service, right?

The usual convenience (i.e. antivirus brought up previously) is that monitored gui runs for every user. And having a process running with privileges in the background I suppose you are able to discern which of your monitored processes runs under which user.

To be honest I don't think it is a nice way of implementing any solution but that's the only way that comes to mind right now.

JonB

@artwaw
You can "monitor" a process from a service, but I don't see how that relates to what the OP is wanting.

The example for anti-virus just seems to be: the non-UI part of the AV runs as a service (with privileges), the user chooses to fire up a user-process UI which happens to communicate with it. The UI process is fully user-level, nothing special about it, so far as I know. I don't think that is what the OP is asking for. But we shall see.

artwaw

@JonB That's essentially what I wanted to say about the design, yes. And that would be my advice on how to implement functionality - using two processes: a monitor and a user-space gui. Unless Windows allows service to span a privileged process that a user can't interfere with but that's not a knowledge I possess.

franco.amato

@JonB no is not what I asked. You should re read my first post.

SGaist

Hi,

One possible cheat is that you use a QProcess to start a new instance of your application if somebody stops it.
From a design point of view, you can forbid your user to close the application by handling the close event yourself. A starting point might be the QSystemTrayIcon example.
Note that this does not protect your application from getting killed but you can still handle the usual interruption signals.
The system service + client application combo is still worth exploring as you can have the service providing the core functionality and the application being merely a front-end.

JonB

@franco-amato said in Qt service with gui:

You should re read my first post.

I have read it many times, thanks. Best of luck showing a UI from a Windows service.

franco.amato

@JonB said in Qt service with gui:

@franco-amato said in Qt service with gui:

You should re read my first post.

I have read it many times, thanks. Best of luck showing a UI from a Windows service.

If you had read it you would have seen that I stated the following: "I know that a Windows service usually doesn't have a GUI and I'm not sure it can have one". What I asked is whether the path of service is the right path or if there are other solutions to achieve my need

JonB

@franco-amato said in Qt service with gui:

If you had read it

Thanks again. It's always nice to try to help people, just what we like to hear.

I read your post carefully, as I said. All I ever answered was that I think you will find it difficult to run a UI from a service. You asked if that was the "right path", I suggested it is not. Sorry if you didn't want to hear that. Why don't you leave me out now, thanks.

franco.amato

@SGaist Can you help with a small example regarding this "One possible cheat is that you use a QProcess to start a new instance of your application if somebody stops it." ?

SGaist

// rest of the code
int result = app.exec();
QProcess::startDetached("your_application");
return result;

franco.amato

@SGaist said in Qt service with gui:

// rest of the code
int result = app.exec();
QProcess::startDetached("your_application");
return result;

It worked but now I am not able to stop it anymore :)) and I am the admin

SGaist

You will have to implement some checks to determine who stopped the application.

Note that you also need to implement graceful shutdown for when you stop/restart your machine.