线程同步互斥机制练习

一、创建两个线程，一个线程打印字符串，另一个线程逆置字符串，要求顺序执行。例如：str[]="1234567"，打印1234567后紧跟7654321。

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

char buf[]="1234567";
sem_t sem_pri;
sem_t sem_rev;

void *callBack1(void *arg)
{
	while(1)
	{
		sem_wait(&sem_pri);
		fprintf(stderr,"%s\n",buf);
		sem_post(&sem_rev);
	}
}
void *callBack2(void *arg)
{
	while(1)
	{
		sem_wait(&sem_rev);
		char *p = buf;
		char *q = p+strlen(buf)-1;
		while(p<q)
		{
			*p=*p^*q;
			*q=*p^*q;
			*p=*p^*q;
			p++;
			q--;
		}
		sem_post(&sem_pri);
	}
}

int main(int argc, const char *argv[])
{
	if(sem_init(&sem_pri,0,1) < 0)
	{
		perror("sem_init");
		return -1;
	}

	if(sem_init(&sem_rev,0,0) < 0)
	{
		perror("sem_init");
		return -1;
	}

	pthread_t tid1,tid2;
	if(pthread_create(&tid1,NULL,callBack1,NULL) != 0)
	{
		fprintf(stderr,"pthread_create failed __%d__",__LINE__);
		return -1;
	}
	if(pthread_create(&tid2,NULL,callBack2,NULL) != 0)
	{
		fprintf(stderr,"pthread_create failed __%d__",__LINE__);
		return -1;
	}
	while(1)
	{}
	return 0;
}

二、创建两个线程，其中一个线程读取文件中的数据，另一个线程将读取到的内容打印在终端上。

方法一：

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

int fd;
char c;
sem_t sem_r,sem_w;
int res = -1;

void *callBack1(void *arg)
{
	while(1)
	{
		sem_wait(&sem_r);
		if(read(fd,&c,1) == 0)
		{
			res = close(fd);
			sem_post(&sem_w);
			break;
		}
		sem_post(&sem_w);
	}
	printf("线程1准备结束\n");
	pthread_exit(NULL);
}
void *callBack2(void *arg)
{
	while(1)
	{
		sem_wait(&sem_w);
		if(res == 0)
			break;
		write(1,&c,1);
		sem_post(&sem_r);
	}
	printf("线程2准备结束\n");
	pthread_exit(NULL);
}

int main(int argc, const char *argv[])
{
	fd = open("1.txt",O_RDONLY);
	if(fd < 0)
	{
		perror("open");
		return -1;
	}

	if(sem_init(&sem_r,0,1) < 0)
	{
		perror("sem_init");
		return -1;
	}
	if(sem_init(&sem_w,0,0) < 0)
	{
		perror("sem_init");
		return -1;
	}
	pthread_t tid1,tid2;
	if(pthread_create(&tid1,NULL,callBack1,NULL) < 0)
	{
		fprintf(stderr,"pthread_create falied __%d__",__LINE__);
		return -1;
	}
	if(pthread_create(&tid2,NULL,callBack2,NULL) < 0)
	{
		fprintf(stderr,"pthread_create falied __%d__",__LINE__);
		return -1;
	}
	pthread_join(tid1,NULL);
	pthread_join(tid2,NULL);

	return 0;
}

方法二： 

#include <stdio.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int fd;
pthread_t tid1,tid2;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER; //创建一个条件变量
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; //创建一把互斥锁
int flag = 0;
char c;
int res = -1;
void *callBack1(void *arg)
{
	while(1)
	{
		pthread_mutex_lock(&mutex);
		if(flag != 0)
		{
			pthread_cond_wait(&cond,&mutex);
		}
		if(read(fd,&c,1) == 0)
		{
			res = close(fd);
			flag = 1;
			pthread_cond_signal(&cond);
			pthread_mutex_unlock(&mutex);
			break;
		}
		flag = 1;
		pthread_cond_signal(&cond);
		pthread_mutex_unlock(&mutex);
	}
	pthread_exit(NULL);
}
void *callBack2(void *arg)
{
	while(1)
	{
		pthread_mutex_lock(&mutex);
		if(flag != 1)
		{
			pthread_cond_wait(&cond,&mutex);
		}
		if(res == 0)
			break;
		write(1,&c,1);
		flag = 0;
		pthread_cond_signal(&cond);
		pthread_mutex_unlock(&mutex);
	}
	pthread_exit(NULL);
}
int main(int argc, const char *argv[])
{
	fd = open("1.txt",O_RDONLY);
	if(fd < 0)
	{
		perror("open");
		return -1;
	}
	//创建两个分支线程
	if(pthread_create(&tid1,NULL,callBack1,NULL) < 0)
	{
		fprintf(stderr,"pthread_create failed __%d__",__LINE__);
		return -1;
	}
	if(pthread_create(&tid2,NULL,callBack2,NULL) < 0)
	{
		fprintf(stderr,"pthread_create faided __%d__",__LINE__);
		return -1;
	}
	pthread_join(tid1,NULL);
	pthread_join(tid2,NULL);
	pthread_cond_destroy(&cond);
	pthread_mutex_destroy(&mutex);
	return 0;
}