pthread_create后子线程输出了两次

#include
#include
#include
#include
#include

void *start_handler(void *);

int main(void)
{
pthread_t tid;
int err;

    if(err = pthread_create(&tid, NULL, start_handler, NULL))
    {
            fprintf(stderr, "Create thread: %s\n", strerror(err));
            return -1;
    }

    printf("OK\n");

    return 0;

}

void *start_handler(void *arg)
{
int err;

    if(err = pthread_detach(pthread_self()))
    {
            fprintf(stderr, "Detach thread: %s\n", strerror(err));
            pthread_exit((void *)-1);
    }

    printf("Start!\n");

    pthread_exit((void *)1);

}

输出了两次是什么？线程函数执行了，然后输出？