开一次资源，用互斥锁记录偏移量要求用两个线程拷贝。A线程拷贝前半部分，B线程拷贝后半部分，不允许使用sleep函数

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




struct pthread
{
	int fd_r;
	int fd_w;
	off_t size;

};
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
void * callB(void * arg)
{   	int fd_r = ((struct pthread*)arg)->fd_r;
	int fd_w = ((struct pthread*)arg)->fd_w;
	off_t size =( (struct pthread*)arg)->size;
		
off_t	offset = 0;
	
	char c= 0;
	for(int  i = 0;i<size/2;i++)
	{      pthread_mutex_lock(&mutex);
		lseek(fd_r,offset,SEEK_SET);
		lseek(fd_w,offset,SEEK_SET);
		

		if( read(fd_r,&c,1)<0)
		{
			perror("read");
			return NULL;
		
		}
		if(write(fd_w,&c,1)<0)
		{
			perror("write");
			return NULL;
		
		}
		offset = lseek(fd_r,0,SEEK_CUR);
		pthread_mutex_unlock(&mutex);
	}
	printf("前面拷贝完成\n");
	pthread_exit(NULL);
}

void * callA(void * arg)
{   	int fd_r = ((struct pthread*)arg)->fd_r;
	int fd_w = ((struct pthread*)arg)->fd_w;
	off_t size =( (struct pthread*)arg)->size;
		
off_t	offset = size/2;
	
	char c= 0;
	for(int i = size/2;i<size;i++)
	{      pthread_mutex_lock(&mutex);
		lseek(fd_r,offset,SEEK_SET);
	lseek(fd_w,offset,SEEK_SET);
		

		if( read(fd_r,&c,1)<0)
		{
			perror("read");
			return NULL;
		
		}
		if(write(fd_w,&c,1)<0)
		{
			perror("write");
			return NULL;
		
		}
		offset = lseek(fd_r,0,SEEK_CUR);
		pthread_mutex_unlock(&mutex);
	}
	printf("后半拷贝完成\n");
	pthread_exit(NULL);
}



int main(int argc, const char *argv[])
{
	//定义两个文件描述符
	int  fd_r,fd_w;	
	//读取文件
	if 	((fd_r = open("./1.text",O_RDONLY)) < 0 )
		{
			perror("open");
			return -1;
		}
	if 	((fd_w = open("./2.text",O_WRONLY|O_CREAT|O_TRUNC,0664)) < 0 )
		{
			perror("open");
			return -1;
		}
	off_t size = lseek(fd_r,0,SEEK_END ); 
	struct pthread p;
	p.size = size;
	p.fd_r = fd_r;	
	p.fd_w = fd_w;
	pthread_t thread1,thread2;	
	if( pthread_create(&thread1,NULL,callB,&p)!= 0)
	{
		perror("callB");
		return -1;
	
	}

	if	(pthread_create(&thread2,NULL,callA,&p)!=0)
	{
		perror("callA");
		return -1;
	
	}

	pthread_join(thread1,NULL);
	pthread_join(thread2,NULL);

	close(fd_r);
	close(fd_w);
	pthread_mutex_destroy(&mutex);

	return 0;
}