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user interface, asynchronous objects, garbage collection

From: Marco Maggi
Subject: user interface, asynchronous objects, garbage collection
Date: Sun, 28 Jan 2007 08:34:40 +0100


to plot math function's graphs for my Guile interface to the
GNU Scientific Library (GSL) I  use a Guile interface to the
Tool Command  Language (TCL), Tk and a  TCL extension called
BLT.  Tk handles the X Window GUI.

The superior  Scheme thread  spawns an inferior  thread that
holds a  TCL interpreter; TCL commands are  built as strings
in the  superior thread, handed  to the inferior  thread and

Plot widgets and coordinates  vectors are TCL objects, and I
use proxy GOOPS objects to manage them. The GOOPS things are
protected  by  a  guardian,  and  I  use  the  AFTER-GC-HOOK
mechanism  to  invoke  appropriate  destructors in  the  TCL
interpreter when they are garbage collected.


When writing a Guile-GSL script I code forms like this:

(let* ((x     ...)
       (y     ...)
       (plot  (blt-plot x y ...)))

the GOOPS  proxies are stored  in the LET*  environment, and
this  prevents the  GC to  collect  them while  the user  is
taking a look.

The problem  is that this  solution is not so  user friendly
when  one is  interacting at  the  REPL. The  need to  store
somewhere  the GOOPS  proxies demands  more typing  and mind
handling of variable names:

  gsh> (define (x ...))
  gsh> (define (y ...))
  gsh> ; all right so far
  ; but the following is ugly
  (define p (blt-plot x y ...))

I thought to create "bag"  objects in which plot proxies are
automatically stored by BLT-PLOT, so the user does something

  gsh> (blt-plot-auto-collect #t)


  gsh> (blt-plot-auto-collect 'name-of-bag)

and then I need a global collection of bags, so that one can

  gsh> (blt-plot-delete 'name-of-bag)


  gsh> (blt-plot-delete #t)

No matter how  I turn it, it seems to me  that I am imposing
to the user to remember annoying things.

AFAIK, GNU Octave does not even try to do this: it just lets
the user  see one plot at a  time.  And Mathlab/Simulink(tm)
just spawns  GUI windows and  lets the user destroy  them by
clicking on the X button.

So, I  wonder if  someone has already  found a  solution for
this. Suggestions are welcome.

Marco Maggi

"They say jump!, you say how high?"
Rage Against the Machine - "Bullet in the Head"

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