4508l3

Listing 3. Allocating Threads

int main (int argc, char *argv[]){
  int num_threads(2);
  // were we called properly?
  if (argc<3)
    usage(argv[0]);
  if (argc==4)
    num_threads=atol(argv[3]);

  try {
    pthread_t *t_id=new pthread_t[num_threads];
    CountPrimes **counter=
                 new CountPrimes*[num_threads];
    // start up the threads
    long start(atol(argv[1]));
    long stop(atol(argv[2]));
    long incr((stop-start)/num_threads);
    for (int i=0; i<num_threads; i++){
      counter[i]=new CountPrimes(start,
             (start+incr)>stop?stop:start+incr);
      start+=incr+1;
      pthread_create(&t_id[i],NULL,
                  counter[i]->entry,counter[i]);
    }
    // now wait for the results
    long count=0;
    for (int i=0; i<num_threads; i++){
      void *return_val;
      pthread_join(t_id[i],&return_val);
      count+=*(reinterpret_cast<long*>(return_val));
      delete reinterpret_cast<long*>(return_val);
    }
    for (int i=0; i<num_threads; i++)
      delete counter[i];

    delete[] counter;
    delete[] t_id;

    if (count>1){
      cout << "There were " << count;
      cout << " primes." << endl;
    }        
    else{
      cout << "There was " << count;
      cout << " prime." << endl;
    }
  }
  catch (range_error e){
    cout << "Exception: " << e.what() << endl;
    exit(EXIT_FAILURE);
  }
  return EXIT_SUCCESS;
}