Re: delwin() and deleting windows with subwindows

[G. Branden Robinson]

At 2022-08-11T12:35:49-0400, Bill Gray wrote:
> On 8/10/22 20:08, Thomas Dickey wrote:
> > it depends: in the SVr4 code, child-windows have a link to their
> > parent, using that to maintain a reference count -- and tell it if
> > there are no remaining children, and return an error if any remain.
> > But that's not enough to just delete all of the children and the
> > parent window, which would make it nice(r) for applications.
> 
>    Well,  yes... nicer,  and apparently we _should_ recursively delete
>    to follow the XSI Curses standard ("It [delwin] must delete
>    subwindows before deleting their parent.")
> 
>    The only downside I see to recursive deletion would be if you did
>    the following :
> 
>    WINDOW *win = newwin( ...);
>    WINDOW *sub = subwin( win, ...);
> 
>    delwin( win);
>    access something in sub;
> 
>    At present,  the delwin() call would fail in ncurses and SVr4.  In
>    PDCurses and Solaris X/Open curses,  win would be deleted and sub
>    wouldn't.  In either case,  attempts to access something in sub
>    will still work.
> 
>    Delete subwindows recursively,  and that access attempts to read
>    freed memory.  One shouldn't be doing such things;  once a parent
>    window is deleted,  you shouldn't try to do anything with the
>    subwindow.  But I'll bet you that some code does so,  and recursive
>    deletion would break that code.

Why not implement recursive deletion for now, and see if anything
squawks?  Any application that chases pointers into freed memory is
surely busted at a fundamental level, quite apart from violating the
documented assumptions of the XSI Curses spec.

Regards,
Branden

signature.asc
Description: PGP signature