Re: proced: ppid of process ID 0 can be 0

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 20 Dec 2008 23:41:00 +0100
> From: "Roland Winkler" <Roland.Winkler@physik.uni-erlangen.de>
> Cc: lekktu@gmail.com, emacs-devel@gnu.org
> 
> On Sun Dec 21 2008 Eli Zaretskii wrote:
> > > I mean, it seems to me that ultimately the solution is always the
> > > same: when using the ppid attribute, one needs to make sure that it
> > > is different from the corresponding pid. Or could one assign a
> > > special meaning to the case that ppid=pid? There is no doubt that
> > > proced assumes that ppid is always different from pid.
> > 
> > Why do you need to assume that?  Is that only to determine whether a
> > given process is the root of the process tree?  If so, a more portable
> > way of doing that would be to have a primitive for that with a
> > system-dependent implementation.
> 
> It's the definition of a tree

Yes, but nobody said that looking at ppid you will have a proper tree.

> - it may return a ppid that equals pid, so that one needs to handle
>   this case appropriately, if necessary, on the lisp level,
> 
> - it may return no ppid, if strictly speaking there is no parent
>   process
> 
> - it may return a ppid of zero, which is the current behavior under
>   GNU/linux
> 
> - some or all the above options are "legal" and its up to the user
>   to handle these possibilities appropriately
> 
> Is there any possiblity missing?

Maybe not, but that's not what I was asking.  I was asking why you
need the assumption about this behavior.  I now understand that it is
only for handling processes as a tree.  So I will write a primitive
for the root of that tree that Lisp code should use for such
decisions.