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Comment by hombre_fatal | Hacker News Reader

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hombre_fatal

Which desktop?

It's not true for AppKit, SwiftUI, GTK, Qt, WinUI, or Electron, and I'm not sure what's left.

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Electron requires effort to get single instance. I've had to implement it. You need to call this:

https://www.electronjs.org/docs/latest/api/app#apprequestsin...

and handle this event:

https://www.electronjs.org/docs/latest/api/app#event-second-...

I believe macos is the only OS that enforces single instance by default. If you start xterm five times on linux, you get five independent xterm processes.

It's standard for Windows. Double click a .exe, and a new copy loads and runs. If it wants to quit because there's an existing instance running, the code has to arrange for that itself. (It's possible Qt does this for you by default. Depending on the app, this can simplify some things, sometimes! Maybe WinUI is the same.)

It looks like macOS Finder tries to make it difficult to run two copies of a .app simultaneously, so I imagine many programs don't check for this case, but this is Hacker News, so we can use our hacker skills to try and do what they don't want us to: find the exe inside the bundle and run it directly from Finder, or run it from the terminal using its path. (This works for me with Ptacek's mdv app. Two copies of it end up in the dock.)

What? 99% of my programs I can open more than one window by just executing the program as normal multiple times, the only ones that enforce a kind of singleton execution are things that also acts as a kind of server, one example is Everything search, but it has a "Open new Search window" for multiple windows. And that is the default, you have to explicit code in a lock/global mutex thing to block multiple instances.

vscode, electron app, no problem opening multiple windows. Geany, gtk app, no problem opening multiple windows.

Can you give an example where this doesn't work?

Anything from WhatsApp to the Settings app on macOS where I might want to, say, compare the wifi network settings for two access points.

But the point is that the developer has to build the app in a way that lets you do this.

Once again, there is no default with the tools I listed. You decide on how you want windowing to work and then build it.

At this point, show me examples of needing a mutex to "block" a multi-window default.

I don't get it. Let's say you create a game.exe, a windows application with a single window. User double clicks on game.exe icon on their desktop, and the window opens. User double clicks the icon again, and the game window opens again. If the developer want to prevent two instances of game.exe running at once, they need to actively detect and prevent this behaviour.

Just like you can start vim several times you can start gvim several times and have a few windows. This is the default behavior, and if the developer wants to change this for some reason, they need to put in some effort.

Maybe macOS is special? I'm not familiar with this platform.

Not on Mac OS, opening more than one instance is undefined behaviour. It may work, but it may also corrupt your data.

I don't know much about macOS. I only used other people's stuff and navigating it is really hard for me.

You're wrong about GTK, Qt, WinUI and Electron though. They default to "do nothing" which eliminates the ability to even know that another instance exists. You have to manually program that.

Huh? None of these force single-instance by default

They don't do anything by default. The developer makes it do what the developer wants (not the user). You claimed the developer has to "actively block it" which isn't the case.

Even in SwiftUI which has the simplest way to support multiple windows with zero work, the developer has to use WindowGroup, and if they didn't then you don't get to open more than one window.

I did not claim it (another user did), but I think your reaction captures the overall sentiment ITT, which is taking perceived status quo as some fundamental thing and defending the worse solution instead of changing the status quo. If all that energy went into perfecting GUI apps the way you want them to work, the ecosystem would have been much healthier. I've seen it in Electron already, and TUI apps are headed the same way, it's simply inevitable. The JS and Python bloat and fragmentation of conventions are already there, reinventing things that used to be simple in a complex way is next (in a way it already happened, e.g. a ton of basic things like hotkey schemes have to be reinvented from scratch each time in TUIs).

I don't understand what you're responding to.

TUI apps are multi-instance by default since the user can invoke the program in different pty sessions. The developer would have to actively fight that.

GUI SDKs generally require the developer to pick a solution. And it's easier to default to the simpler solution where you have one instance, one data model, one window.

Whether things might change in the future isn't relevant because we're talking about how things are today, not speculating about the future. And the time to change one's opinion is when reality changes, not ahead of time based on how you think things hopefully will be.

> GUI SDKs generally require the developer to pick a solution. And it's easier to default to the simpler solution where you have one instance, one data model, one window.

I don't know which GUIs you have programmed but for Windows and GNU/Linux this isn't the simplest option. It requires quite the effort to actually enforce single instance.

The developer (of the app or the app framework) does have to deliberately implement "merging" of a second launched process. The default would be for the two processes to run side by side in both Windows and Linux. It has been that way forever.

The merging behaviour is also in principle possible for TUIs, btw, it's just that nobody does it. But with something like tmux is would be easy to set up that all subsequent calls to your binary actually connect to the already open session launched by the first instance.

You appear to be conflating multiple windows in a single process with multiple processes. The default is that each process is almost entirely isolated from the rest of the running system. You have to actively work to even detect that another instance of the program you wrote is running.

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