[GRASSLIST:3161] Re: [GRASS5] Re: Grass GUI

Roger Miller rgrmill at rt66.com
Sun Feb 17 15:03:44 EST 2002

On Sunday 17 February 2002 12:09, Glynn Clements wrote:
> Roger Miller wrote:
> > It includes changes to a small number of library functions that allows
> > more flexibility.  It arranges for G_get_window and other window
> > functions to always provide information about the window settings of the
> > currently selected monitor, not from the database WIND files.
> How does it handle the case where no monitors are running?

It uses a "nulll" monitor.  The first monitor that is started inherits it's 
window setting from the null monitor.  All subsequent monitors inherit their 
window settings from the currently selected monitor. 

> Also, I'm not sure what this change would enable. You still can't have
> multiple sessions using the same mapset directory due to the lack of
> any finer-grained locking.

The proposal isn't intended to allow multiple simultaneous access to a single 
mapset.  It is intended to allow a single user to use multiple monitors to 
access two or more mapsets within one session, and to use two or more 
different window settings simultaneously, even while working in one mapset. 

> If the locking issue were solved, the simplest way to support multiple
> sessions on a single mapset would be to merge the data in the WIND
> files with most of the data in $GISRC into a "session" file.

The proposal is intended to do that, but it uses virtual memory instead of 
creating a file.  I'm not sure that really solves any locking issues, because 
ultimately the session settings need to be saved back to the WIND file.

Improved locking is an issue that I think GRASS needs to address eventually.  
My proposal does not address it.  One possible approach would give the user 
read-write access to anything in one mapset, but read only access in 
everything else.

> However, note that there is an inherent tension between having
> multiple sessions on a single mapset and remembering a mapset's region
> between sessions.

Yes, that's a problem.

> > The final capability I
> > intended to add before I presented the program allows each monitor to be
> > associated with an entirely different GIS environment.  That allows a
> > user to display and work with data from more than one mapset and more
> > than one database location at the same time.
> AFAICT, the only thing that imposes a "one session per user" limit is
> the way that $GISRC is managed. You can have multiple sessions,
> provided that you create a new $GISRC file for each one.

I don't think that one user running multiple sessions is a better alternative.

Roger Miller

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