[petsc-dev] Use of the DISPLAY environment variable

[Satish Balay]

On Sun, 29 Aug 2010, Barry Smith wrote:

> 
> On Aug 29, 2010, at 2:45 PM, Jed Brown wrote:
> 
> > PETSc uses the -display option differently from the DISPLAY environment
> > variable.  In particular, it prepends the hostname when DISPLAY starts
> > with ":".
> > 
> >  ierr = PetscOptionsGetString(PETSC_NULL,"-display",PetscDisplay,256,&flag);CHKERRQ(ierr);
> >  if (flag) PetscFunctionReturn(0);
> > [...]
> >    str = getenv("DISPLAY");
> >    if (!str || (str[0] == ':' && size > 1)) {
> >      ierr = PetscGetHostName(display,255);CHKERRQ(ierr);
> >      ierr = PetscStrcat(display,":0.0");CHKERRQ(ierr);
> >    } else {
> >      ierr = PetscStrncpy(display,str,256);CHKERRQ(ierr);
> >    }
> > 
> > Is this really the right thing (ignoring the small overflow
> > possibility)?  Why not concatenate hostname with the value of DISPLAY
> > when it starts with ':'?
> 
>    I'm not sure why it was set to always use :0.0 there. Yes it sounds reasonable to use DISPLAY there.
> > 
> > But more importantly, firewalls are frequently set up to block port
> > 6000, so DISPLAY=hostname:0.0 won't work, but DISPLAY=:0.0 will work
> > (obviously only among local nodes).  I've just gotten used to always
> > running with -display :0 in parallel, but how about reducing the
> > hostname to check whether it is the same on all hosts.  If so, then just
> > use DISPLAY as is.  This would make graphics Just Work on more systems.
> 
>     This sounds fine.
> 
>    Barry
> 
> > 
> > Does this sound reasonable?

Yes - I like this change [and also remove all the extra stuff] in this
routine.

It  was  tailored for one type of setup that probbly doesn't exist anymore.

As you say - the more common setup [which --download-mpich
etc. default to] is to run all procs on the same node - so perhaps
the following code is sufficient.

>>>>>>
  str = getenv("DISPLAY");
  if (str) {
    ierr = PetscStrncpy(PetscDisplay,str,256);CHKERRQ(ierr);
  } else {
    ierr = PetscStrncpy(PetscDisplay,":0.0",256);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
<<<<<

Satish