Where is my logic failing?

Question

I am done the work-- but my output is odd. I am basically trying to compare a bunch of objects and if they share ttns and their time is up-- then they need to recalculate their ttns. After checking all the hosts I increment the clock and try again. The objective is to find the fist host which can make it through the check without a collision. This is basically a simulation of a network that does some backoff calculation if two hosts send at the same time (CLOCK). I put in a check to ensure the host didn't check itself-- I know what my expected output is and it isn't it. I have worked through this a few times but can't find my logic error(s). Any pointers?

// Should insert n number as argument 1 on the command line. 
#include <iostream>
#include <vector>
#include <stdlib.h> // srand(), time()

static int CLOCK = 0;

class Host{
  private:
    int sid;
    int cc;
    int ttns;

  public:
    Host();
    int get_sid(){ return sid; }
    void set_sid(int id){ sid = id; }
    int get_cc(){ return cc; }
    void inc_cc(){ cc += 1; }
    int get_ttns(){ return ttns; }
    void new_ttns(){ ttns = (rand()%(cc+1))+CLOCK+1; }
  };

Host::Host(){
  sid  = -666;
  cc   = 0;
  ttns = 0;
}

bool work(std::vector<Host> &hosts){
  int count = 0;

  for(CLOCK = 0; /*INFINITE*/; CLOCK++){
      for(int i = 0; i < hosts.size(); i++){
        count = 0;
          for(int n = 0; n < hosts.size(); n++){
              if( (i != n) && /* host i doesn't compare to host n */
                  (hosts[i].get_ttns() == hosts[n].get_ttns()) &&/* host i and n share ttns */ 
                  (hosts[i].get_ttns() == CLOCK)  /* host i ttns = now */
                ){ 
                hosts[i].inc_cc();
                hosts[i].new_ttns(); 
                count = -666; // collision occured
              }
          count++;
          }
        if ( count == hosts.size() ){
          std::cout << "Host " << hosts[i].get_sid() << "\nTTNS: " << hosts[i].get_ttns();
          std::cout << std::endl;
          return false;
        }
     } 
  }

  return true; // pretty pointless
}

int main(int argc, char *argv[]){
  srand(time(NULL));
  std::vector<Host> hosts;

  // Push hosts into vector
  int nhosts = atoi(argv[1]);
  for(int i = 0; i < nhosts; i++){
    Host newhost;
    newhost.set_sid(i);
    hosts.push_back(newhost);
  }

  while (work(hosts)){
    ; // hang out 
  }

  return 0;
}

Answer 1

It seems to me you should update the cc and ttns for the host n you are checking for in the inner loop.

            hosts[n].inc_cc();
            hosts[n].new_ttns(); 

Instead of

            hosts[i].inc_cc();
            hosts[i].new_ttns(); 

And move the check for

    ( hosts[i].get_ttns() == CLOCK )

outside the inner loop.

    if ( hosts[i].get_ttns() == CLOCK )
      for(int n = 0; n < hosts.size(); n++){

The condition inside then becomes

           if( (i != n) && /* host i doesn't compare to host n */
              (hosts[i].get_ttns() == hosts[n].get_ttns()) /* host i and n share ttns */
           ){

This way you don't count++ for invalid hosts.

Answer 2

one of the error is probably in this line:

(hosts[i].get_ttns() == CLOCK)

you can't compare this, since CLOCK is global and incremented by more than one host. that means a host doesn't have a monotonous CLOCK.

maybe you want this:

(hosts[i].get_ttns() <= CLOCK