Thread: multithreading question

The example output was multiplying two 25x25 arrays with 25 threads available. Since then I've changed the code like this:

Code:

void *matmult(void *ptr) {
  int i, j, pos = (int)ptr;
  while (rowcount < m - 1) {
    pthread_mutex_lock(&mutex);
    if (rowcount < m - 1)
      ++rowcount;
    else {
      pthread_mutex_unlock(&mutex);
      return NULL;
    }
    pthread_mutex_unlock(&mutex);
    sleep(1); //lets other threads into queue before running and going back
    printf("thread %d is processing row %d\n",pos,rowcount);
    for (i = 0; i < k; ++i) {
      C[rowcount][i] = 0;
      for (j = 0; j < n; ++j)
        C[rowcount][i] += B[rowcount][j] * A[j][i];
    }
  }
}

and the thread creation code like:

Code:

  pthread_t *tid = new pthread_t[numthreads];
  for (i = 0; i < numthreads; ++i)
    pthread_create(&tid[i],NULL,matmult,(void*)i);
  for (i = 0; i < numthreads; ++i)
    pthread_join(tid[i],NULL);

These changes make it so that each thread is actually identified, and they step through the rowslike I had in mind. (0 1 2 3 0 1 2 3 0 1 2 3) etc. Still, I agree that replacing sleep with sched_yield would be a better solution, but that'll have to wait until I get back to school to try out.