Re: [Tinyos-help] TOSSIM Crash with sim_gain_remove

[J. Ryan Stinnett]

Philip Levis wrote:
On Jul 24, 2007, at 11:48 AM, J. Ryan Stinnett wrote:
I'm trying to find a way to change the gain of a radio link in TOSSIM 
(from CVS) midway through the simulation.  I didn't see a function 
specifically for changing the gain of a link already added, so I 
thought I would remove the original link and re-add it with a new 
gain. Something like this in C (this is a bit contrived):

Tossim* t = new Tossim(NULL);

t->radio()->add(0, 1, -50);
t->radio()->add(1, 0, -50);
t->radio()->add(1, 2, -120);
t->radio()->add(2, 1, -50);

for (int i = 0; i < 10000; i++)
  t->runNextEvent();

t->radio()->remove(1, 2);
t->radio()->add(1, 2, -50);

for (int i = 0; i < 10000; i++)
  t->runNextEvent();

However, I get a segfault when trying to remove the link.  I believe 
this is because of a bug in sim_gain_remove() when you remove the link 
most recently added for a given source.  I tried to fix that, but then 
I just ended up with other crashes when messages were trying to be 
sent and such.  Any ideas?

There's a bug in the remove function, pertaining to updating the linked 
list on a remove. Try this:

void sim_gain_remove(int src, int dest) __attribute__ ((C, spontaneous))  {
  gain_entry_t* current;
  gain_entry_t* prevLink;
  int temp = sim_node();

  if (src > TOSSIM_MAX_NODES) {
    src = TOSSIM_MAX_NODES;
  }

  sim_set_node(src);

  current = sim_gain_first(src);
  prevLink = NULL;

  while (current != NULL) {
    gain_entry_t* tmp;
    if (current->mote == dest) {
      if (prevLink == NULL) {
        connectivity[src] = current->next;
      }
      else {
        prevLink->next = current->next;
      }
      tmp = current->next;
      sim_gain_deallocate_link(current);
      current = tmp;
    }
    else {
      prevLink = current;
      current = current->next;
    }
  }
  sim_set_node(temp);
}


Phil



Thanks, that takes care of it!  Actually, that's basically how I tried 
to fix it myself, so I'm not sure what I did differently...  In any 
case, it's working fine now.

Thanks,
Ryan
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