多线程按照线程顺序打印字符

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

int num = 0;
pthread_mutex_t mutex_lock = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond_ready = PTHREAD_COND_INITIALIZER;

void *output_chara(void *arg)
{
int i;
int cond_num = (int) arg;

for (i = 0; i < 10; i++){
pthread_mutex_lock(&mutex_lock);
while (num != cond_num){
pthread_cond_wait(&cond_ready, &mutex_lock);
}

printf("%c", 'A' + cond_num);

num = (num + 1) % 3;

pthread_mutex_unlock(&mutex_lock);
pthread_cond_broadcast(&cond_ready);
}
}

int main()
{
int i;
pthread_t tid[3];

for (i = 0; i < 3; i++){
pthread_create(&tid[i], NULL, output_chara, (void *)i);
}

for (i = 0; i < 3; i++){
pthread_join(tid[i], NULL);
}

return 0;
}

ABCABCABCABCABCABCABCABCABCABC