Closing :observer.start() window on macOS doesn't kill the app

Prob belongs under erlang but here goes

screenshot

> iex -S mix
Erlang/OTP 23 [erts-11.1.7] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]

Interactive Elixir (1.11.3) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> :observer.start()
:ok

So far so good.

Observer docs indicate that to shutdown:

Module

observer

Exports

start() → ok
OTP R15B

Starts the Observer GUI. To stop the tool, close the window.

Say no more, so I go ahead and close the window, but the app remains on the dock.

Right click app on dock and click Quit, nothing happens.

Run :observer.start() again now that window is closed, nothing happens.

Force quit the erlang app, I get the following

iex(2)> 
13:28:01.365 [info]  SIGTERM received - shutting down

[1]    70302 killed     iex -S mix

Does this mean the erlang macOS app I see in dock is the actual iex session, not the observer? Or does it just mean that iex session process is linked to observer process?

Expected behavior behavior: on window close, tool gets stopped, app removed from dock, iex receives message and keeps running. Then, in same iex session, on second :observer.start() call, tool starts anew with app in dock.

Any ideas how to fix?

My solution: Ignore the app icon. I‘ll go away once you close the iex session.

It is because of the architecture of macOS and the limitation that only root PID can create window. So in fact, closing the window didn’t closed the “application” (from the OS point of view) as the PID is still there (ERTS need to do some special-case handling for macOS to make it work).

What if I’d like to reopen :observer? Do I need to kill entire iex session?

Do you mean this is the case with other mac apps as well?

Just like there are many mac apps out there, which can run without having a window open so can the beam. Opening another observer will simply open a new observer window. Think of observer less like a separate app to your shell, but more like your shell is also a program rendering windows.

That’s the issue.

I am not able to reopen :observer window after having closed it

Ah, if I do rightclick → Quit then it doesn’t work for me as well. If I just close the observer window itself then I can open new windows. Seems like trying to quit the observer sends the mac application into cleanup mode, which then waits for iex to shut down, which never happens.

1 Like

When

I cannot reopen it from shell, i.e. calling :observer.start() does not relaunch new window

What Erlang and macOS version you are at? Because it works for me.

Erlang/OTP 23 [erts-11.1.7]

macOS 11.2.1