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

pthread_mutex_t mutex=PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond=PTHREAD_COND_INITIALIZER;
int set=0;

void* fun1(void* arg)
{
	pthread_mutex_lock(&mutex);
	while(set!=1)
		pthread_cond_wait(&cond,&mutex);
	set=2;
	printf("A\n");
	pthread_cond_broadcast(&cond);
	pthread_mutex_unlock(&mutex);
}
void* fun2(void* arg)
{
	pthread_mutex_lock(&mutex);
	while(set!=0)
		pthread_cond_wait(&cond,&mutex);
	set=1;
	printf("B\n");
	pthread_cond_broadcast(&cond);
	pthread_mutex_unlock(&mutex);
}
void* fun3(void* arg)
{
	pthread_mutex_lock(&mutex);
	while(set!=2)
		pthread_cond_wait(&cond,&mutex);
	set=3;
	printf("C\n");
	pthread_cond_broadcast(&cond);
	pthread_mutex_unlock(&mutex);
}
void* fun4(void* arg)
{
	pthread_mutex_lock(&mutex);
	while(set!=3)
		pthread_cond_wait(&cond,&mutex);
	set=0;
	printf("D\n");
	pthread_cond_broadcast(&cond);
	pthread_mutex_unlock(&mutex);
}

int main()
{
	pthread_t tid[4];
	pthread_create(tid+0,NULL,fun1,NULL);
	pthread_create(tid+1,NULL,fun2,NULL);
	pthread_create(tid+2,NULL,fun3,NULL);
	pthread_create(tid+3,NULL,fun4,NULL);
	int i=0;
	for(i=0;i<4;i++)
		pthread_join(tid[i],NULL);
		
	pthread_mutex_destroy(&mutex);
	pthread_cond_destroy(&cond);
}