Homework 8.3 Thread Synchronization Mutex Condition Variables

题目：编写一个程序,开启3个 线程,这3个线程的ID分别为ABC,每个线程将自己的ID在屏幕上打印10遍,要求输出结果必须按ABC的顺序显示,如ABCABC……依次递推;

提示：A只能叫醒B,B只能唤醒C,C只能唤醒A;

实现代码

#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <semaphore.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

//Define three condition variables
pthread_cond_t cond1;
pthread_cond_t cond2;
pthread_cond_t cond3;

//互斥锁
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

void* A(void* arg)
{
    
	for(int i=0;i<10;i++)
	{
    
		pthread_mutex_lock(&mutex);
		printf("A");
		pthread_cond_signal(&cond2);
		pthread_cond_wait(&cond1, &mutex);
		pthread_mutex_unlock(&mutex);
	}	
	pthread_exit(NULL);

}

void* B(void* arg)
{
    
	for(int i=0;i<10;i++)
	{
    
		pthread_mutex_lock(&mutex);
		pthread_cond_wait(&cond2, &mutex);
		printf("B");
		pthread_cond_signal(&cond3);
		pthread_mutex_unlock(&mutex);
	}	
	pthread_exit(NULL);
}

void* C(void* arg)
{
    
	for(int i=0;i<10;i++)
	{
    
		pthread_mutex_lock(&mutex);
		pthread_cond_wait(&cond3, &mutex);
		printf("C");
		pthread_cond_signal(&cond1);
		pthread_mutex_unlock(&mutex);
	}	
	pthread_exit(NULL);
}

int main(int argc, const char *argv[])
{
    
	//Create three condition variables
	if(pthread_cond_init(&cond1, NULL) != 0)
	{
    
		perror("pthread_cond_init");
		return -1;
	}
	if(pthread_cond_init(&cond2, NULL) != 0)
	{
    
		perror("pthread_cond_init");
		return -1;
	}
	if(pthread_cond_init(&cond3, NULL) != 0)
	{
    
		perror("pthread_cond_init");
		return -1;
	}
	printf("Condition variable creation succeeded\n");	
	
	//创建3个线程
	pthread_t tid1,tid2,tid3;
	
	//A线程打印A
	if(pthread_create(&tid1,NULL,A,NULL)!=0)
	{
    
		perror("pthread_creat");
		return -1;
	}
	
	//B线程打印B
	if(pthread_create(&tid2,NULL,B,NULL)!=0)
	{
    
		perror("pthread_creat");
		return -1;
	}
	
	//C线程打印C
	if(pthread_create(&tid3,NULL,C,NULL)!=0)
	{
    
		perror("pthread_creat");
		return -1;
	}
	
	pthread_join(tid1,NULL);
	pthread_join(tid2,NULL);
	pthread_join(tid3,NULL);

	printf("\n");

	//销毁互斥锁
	pthread_mutex_destroy(&mutex);
	//销毁条件变量
	pthread_cond_destroy(&cond1);	
	pthread_cond_destroy(&cond2);
	pthread_cond_destroy(&cond3);
	
	return 0;
}

运行结果