Synchronizing to the termination of a thread

I mentioned that there were a number of problems with the simplistic code sample initially shown. Another problem with it is that main() starts up a bunch of threads and then displays the results. How does the function know when it's safe to display the results?

int main (int argc, char **argv)
{
    ...
    // start threads as before

    while (num_lines_completed < num_x_lines) {
        sleep (1);
    }
}

Don't even consider writing code like this!

There are two elegant solutions to this problem: pthread_join() and pthread_barrier_wait().