questions regarding activity and getCurrentTime()...

[Rick Riolo]

I have a couple of questions, based on some behavior in the
heatbugs demo.  What I did was write this method in HeatSpace.m:

-updateLattice {
        [super updateLattice];

        printf("--> at %lu heat at 20,20 is now %d.\n",
                   getCurrentTime(), [self getValueAtX: 20 Y: 20] );

        return self;
}

The addition of the above is the only change from the heatbugs
as it comes out of swarmapps-1.0.2 (all this with swarm-1.0.5).
That is, I am trying to override updateLattice and 
have it do what it does usually, then have it print
a little message.  But when I then Start heatbugs, I get a
crash with this old familiar message:

badger-rlr)./heatbugs
*** event raised for error: InvalidOperation
*** function: _activity_context_error(), file: XActivity.m, line: 622
> getCurrentTime(): there is no currently running activity from which
> to obtain requested activity context information.
> The context query macros are available only within a> compiled action being 
> executed under a running activity.
> They are not available when the activity is stopped
> or otherwise inactive.
> This includes any external probe request.

So...one thing I don't understand is why it says there is no
currently running activity.  As far as I know, the only place 
updateLattice gets sent to the heatbugs HeatSpace is in the model
activity group:

  modelActions = [ActionGroup create: [self getZone]];
  [modelActions createActionTo:      heat        message: M(stepRule)];
  [modelActions createActionForEach: heatbugList message: M(step)];  
  [modelActions createActionTo:      heat        message: M(updateLattice)];

Note that in another version of heatbugs, in which I have added
a stepReport method for the ModelSwarm object, I do this:

  modelActions = [ActionGroup create: [self getZone]];
  [modelActions createActionTo:      heat        message: M(stepRule)];
  [modelActions createActionForEach: heatbugList message: M(step)];  
  [modelActions createActionTo:      heat        message: M(updateLattice)];
  [modelActions createActionTo:      self        message: M(stepReport)];

What is strange is that in this case, the stepReport method 
calls getCurrentTime(), and that works fine!!
In this version, if I add the -updateLattice override as above,
and change nothing else, it also crashes with the message above.

So....I don't understand what's going on here.
Am I missing some sending of the updateLattice message to HeatSpace
that happens before the schedule starts?
I don't find it if I do a grep in the heatbugs directory.

---------
Now a related question:

If I take that reference to getCurrentTime() out of my overriding
updateLattice, I have:

-updateLattice {
        [super updateLattice];

        printf("--> heat at 20,20 is now %d.\n",
              [self getValueAtX: 20 Y: 20] );

        return self;
}

When I do this it runs fine, but what puzzles me is why it prints
messages like this:

--> heat at 20,20 is now 145.
--> heat at 20,20 is now 145.
--> heat at 20,20 is now 305.
--> heat at 20,20 is now 305.
--> heat at 20,20 is now 458.
--> heat at 20,20 is now 458.

That is, it seems to be printing my little message twice each step.
(Each of those pairs comes from pressing <STEP> once in this case.)
Why does it do that?  Is it really doing updateLattice twice each time step?   
Or is something funny happening because of my use of [super 
updateLattice]?   I know sometimes un-intuitive things can happen,
as in the example on pages 71-73 or so of the ObjectiveC ref manual.
But I don't quite see how it would happen in this case.

Am I missing something obvious in all this?

thanks.
  - r
 
Rick Riolo                           address@hidden
Program for Study of Complex Systems (PSCS)
4068 Randall Lab                
University of Michigan         Ann Arbor MI 48109-1120
Phone: 313 763 3323                  Fax: 313 763 9267
http://www.pscs.umich.edu/PEOPLE/rlr-home.html


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