Another bug (and suggested fix) with dropping BLTGraph...

[mcmullin]

Hmmm...

In a previous message I mentioned that I had a problem
with dropping an EZGraph - namely that the tk frame
didn't get dropped.  I eventually "fixed" that by
adding code to the EZGraph drop to drop the unlying
BLTGraph; and adding code to the BLTGraph drop to drop
the tk frame.  That *seemed* to work fine at first, but
I have run into another (independent?) problem:
dropping the BLTGraph causes a seg fault and the app
crashes (:-(

The BLTGraph drop looks like this:

-(void) drop {
  id index, e;
  index = [elementList begin: [self getZone]];
  while ((e = [index next])) {
    [self destroyElement: e];
  }
  [index drop];
  [globalTkInterp eval: "destroy %s", [parent getWidgetName]]; 
  [super drop];
}

The statement sending the destroy command to
globalTkInterp is the one I added to get rid of the tk
frame.  The seg fault is happening *before* that, in
the loop "destroying" the elements of elementList.

Looking at the destroyElement method, I find that it
basically just removes the element from elementList and
then drops it.  BUT: since indices are not (yet) safe,
this seems to be a bug: removing an element from
elementList will compromise the validity of index.  I
believe this is the cause of the seg fault. (What I
can't really understand is why this hasn't been
encountered by anyone before - unless nobody is ever
dropping BLTGraphs??)

My proposed fix is to change the BLTGraph drop to the
following:

-(void) drop {
  while ([elementList getCount] > 0)
    [self destroyElement: [elementList getFirst]];

  [globalTkInterp eval: "destroy %s", [parent getWidgetName]]; 
  [super drop];
}

This *seems* to work OK in my app and gets rid of the
seg fault I was experiencing.  Of course, your mileage
may vary...

Regards,

Barry.


-- 

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| Barry McMullin, ALife Group,               |    address@hidden |
| Santa Fe Institute, 1399 Hyde Park Road,   |  Voice: +1-505-984-8800 |
| Santa Fe, NM 87501, USA.                   |  FAX:   +1-505-982-0565 |
| http://www.eeng.dcu.ie/~mcmullin           |                         |
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++



                  ==================================
   Swarm-Support is for discussion of the technical details of the day
   to day usage of Swarm.  For list administration needs (esp.
   [un]subscribing), please send a message to <address@hidden>
   with "help" in the body of the message.
                  ==================================