setpriority() test program

#define _GNU_SOURCE

#include <pthread.h>
#include <unistd.h>
#include <time.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/syscall.h>
#include <stdio.h>
#include <stdlib.h>

#define gettid() (syscall(SYS_gettid))

pthread_barrier_t barrier;

static void burn_cpu(char *caller)
{
    long int i = 0;

    while (1) {
        long int foo = mrand48();

        i++;

        if ((i % 10000000) == 0) {
            printf("%s %ld\n", caller, i / 10000000);
        }
    }
}

static void *bg_worker_func(void *arg)
{
    int tid = gettid();

    setpriority(PRIO_PROCESS, tid, 10);

    pthread_barrier_wait(&barrier);

    burn_cpu("bg_worker");

    pthread_exit(NULL);
}

int main( void )
{
    pid_t child;
    pthread_t bg_worker;

    child = fork();

    if (child == 0) {
        pthread_barrier_init(&barrier, NULL, 2);
        pthread_create(&bg_worker, NULL, bg_worker_func, NULL);

        setpriority(PRIO_PROCESS, getpid(), 20);
        pthread_barrier_wait(&barrier);

        burn_cpu("main");

        pthread_join(bg_worker, NULL);
        exit(EXIT_SUCCESS);
    } else {
        sleep(3);
        int rv = setpriority(PRIO_PROCESS, child, 0);
        printf("setpriority called! rv = %d\n", rv);
    }

    exit(EXIT_SUCCESS);
}