How would I rebar3 release a graphical application?

[nixxquality]

Hello,

I'm finishing up a program I made using Erlang's wx bindings and I'm now in the exciting process of "packaging" and "releasing".
You can find the code at: https://gitgud.io/nixx/trackervalidator

There are a few question marks, some more optimistic than others:

1. Can I make this into a single binary? (Signs point to no.)
2. Can I make this easier to run than having to open a terminal and manually entering trackervalidator console in the correct folder?
3. Can I make this run without an extra console window floating around on the side?
4. Why does the Erlang VM still run when the main application ends? I even explicitly marked it as permanent once with no change in behaviour.
5. How would I save settings between runs? Trying to locate and overwrite sys.config both seems like a very easy and very difficult problem at the same time.

Thank you for your responses.

[ferd]

1. no
2. not by default. fancier solutions like creating shortcuts that run things in the background are not something we ever tackled, but releases can be created to be async and less visible
3. yeah, but it requires starting the release either in foreground mode (with the release script) while detaching from the process when it is invoked (eg. $ <command> & in a bash shell), or using the daemon mode (which uses named pipes)
4. "when the application ends" here is ambiguous a bit: the wx windows are held in a distinct set of Erlang processes, and they are allowed to live and die independently from the rest of the system. That's what would, for example, let you open up observer and then kill it without also killing the system it is letting you introspect. My limited understanding is that it would be up to your app in Erlang to monitor the windows (or window destruction events) to know when all the windows are dead and to then call something like init:stop() to fully terminate the program.
5. sys.config is meant for the sort of "boot time" settings that you as someone deploying the software would always want to be true. These values can be changed with sys.config.src to use ENV variables, but that still ties you to a terminal to do it (see https://rebar3.org/docs/deployment/releases/#application-configuration). If you want a fancier configuration mechanism, it will need to be developed individually.

[nixxquality]

The extended_start_script does not include either a foreground or a daemon mode on Windows. By disabling that I got a slightly better script that can just be doubleclicked to launch, but it still pops out a console on the side.

I've already wired it up so that my OTP application terminates when my wx window is closed, but the VM seems to stick around after that. I can even see the system report in the console:

=INFO REPORT==== 31-Jan-2024::18:35:25.580000 ===
    application: trackervalidator
    exited: stopped
    type: permanent

[ferd]

oh Windows is a whole different beast there. I'm not exactly sure what its rules are and I no longer have a functional windows computer to try things with (since they made having a TPM required for OS installs on new versions). I think I saw RabbitMQ do it a few years ago, but the way they did it required registering themselves as a sort of windows service to make it work and it was a lot more complex.

I believe that on Windows START /B <command> is the equivalent to Linux's <command> &. Maybe that will help, but I have no idea and can't test it right now.

If you want your application stop to kill the node, usually having it as type permanent should shut down everything, as per the Erlang/OTP doc:

The application master starts the application by calling the application callback function Module:start/2 as defined by the application specification key mod.

Argument Type specifies the type of the application. If omitted, it defaults to temporary.

• If a permanent application terminates, all other applications and the entire Erlang node are also terminated.
• If a transient application terminates:
  • with Reason == normal, this is reported but no other applications are terminated.
  • abnormally, all other applications and the entire Erlang node are also terminated.
• If a temporary application terminates, this is reported but no other applications are terminated.

Notice that an application can always be stopped explicitly by calling stop/1. Regardless of the type of the application, no other applications are affected.

Notice also that the transient type is of little practical use, because when a supervision tree terminates, the reason is set to shutdown, not normal.

If the application is calling application:stop(AppName) then yeah it will be hanging. If you call init:stop() then the whole node will shut down. If you're calling the latter but things hang, double-check whether kernel and stdlib are in your app file's dependencies; I've seen this hang in the past (like 10 years ago) when that was the case and we added warnings in rebar3 to prevent that.

[nixxquality]

I went digging around the relx repository and I found the hidden {include_start_scripts_for, [powershell]} setting. That one does include a foreground option.

With a bit of messing around, I've now reached a solution that's Good Enough for me: Use the powershell script along with a shortcut that looks something like powershell.exe -WindowStyle hidden ...\trackervalidator\bin\trackervalidator.ps1 foreground. There's still a window that pops up for a second but that's a powershell issue, and can probably be mitigated in another way.

As for the hanging, you were correct. I shouldn't have been calling application:stop manually, when I let my gen_server that holds the wx window terminate on its own the OTP design does work and the VM eventually closes.

That's all my questions addressed, thank you very much.