Order of running threads in pthreads

Question

In the following program, what are the possibilities for the ordering of threads? Assuming "function" will print thread id which is unique (since here we have only one process). I always get the order th1,th2!

#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
int main()
{
            pthread_t th1;
            pthread_t th2;
            pthread_create(&th1, NULL, function, NULL);
            pthread_create(&th2, NULL, function, NULL);
            pthread_join(th1, NULL);
            pthread_join(th2, NULL);
}

   return 0;
}

Answer 1

The only ordering guarantees here are that pthread_join(th1, NULL); will not return until thread 1 has exited and pthread_join(th2, NULL); will not return until thread 2 has exited. Consequently, the main() function will not return (and the process will not exit) until both thread 1 and thread 2 have exited.

There is no ordering imposed between thread 1 and thread 2 - their execution can be arbitrarily interleaved.