두 개의 쓰레드를 동시에 실행하는 방법은?

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
 
void* thread_func1(void* arg)
{
        int i=0;
        for(i=0;i<100;i++)
        {
                printf("thread1:%d\n", i);
        }
 
}
 
void* thread_func2(void* arg)
{
        int i=0;
        for(i=0;i<100;i++)
        {
                printf("thread2:%d\n", i);
        }
 
}
 
void* thread_func2(void* arg);
 
int main(void)
{
        pthread_t thread1;
        pthread_t thread2;
 
        pthread_attr_t thread_attr;
        pthread_attr_init(&thread_attr);
 
        pthread_attr_setschedpolicy(&thread_attr, SCHED_RR);
 
        pthread_create(&thread1, &thread_attr, thread_func1, NULL);
        pthread_create(&thread2, &thread_attr, thread_func2, NULL);
 
        sleep(100);
 
        return 0;
}