多线程拷贝文件

#include <myhead.h>
sem_t sem;

struct filedata
{
	char fileread[20];
	char filewrite[20];
	int len;
};

int get_file_len(const char *srcfile, const char *destfile)
{
	int rd = open(srcfile, O_RDONLY);
	if(rd == -1)
	{
		perror("open file error");
		return -1;
	}

	int wr = open(destfile, O_WRONLY|O_CREAT|O_TRUNC, 0664);
	if(wr == -1)
	{
		perror("create file error");
		return -1;
	}

	int len = lseek(rd, 0, SEEK_END);

	close(rd);
	close(wr);

	return len;
}
void copy_file(const char *srcfile, const char *destfile, int start, int len)
{
	//以只读形式打开文件
	int rd = open("admin.txt", O_RDONLY);
	if(rd == -1)
	{
		perror("open file error");
		return;
	}

	int wr = open("admin2.txt", O_WRONLY);
	if(wr == -1)
	{
		perror("create file error1");
		return;
	}

	lseek(rd, start, SEEK_SET);
	lseek(wr, start, SEEK_SET);

	char buf[128] = "";
	int sum = 0;
	int pid = getpid();
	while(1)
	{
		bzero(buf, sizeof(buf));

		int res = read(rd, buf, sizeof(buf));
		sum += res;
		if(res==0 || sum>=len)
		{
			write(wr, buf, res-(sum-len));
			break;
		}
		write(wr, buf, res);
	}
	close(rd);
	close(wr);
}

void *task1(void *arg)
{
	struct filedata file1;
	sem_post(&sem);
	copy_file(file1.fileread, file1.filewrite, 0, file1.len/2);
	printf("前半复制成功\n");

	pthread_exit(NULL);
}

void *task2(void *arg)
{
	struct filedata file1;
	sem_wait(&sem);
	copy_file(file1.fileread, file1.filewrite, file1.len/2, (file1.len+1)/2);
	printf("后半复制成功\n");

	pthread_exit(NULL);
}

int main(int argc, const char *argv[])
{
	//判断是否传入三个文件
	if(argc != 3)
	{
		printf("input file error");
		return -1;
	}
	int len = get_file_len(argv[1], argv[2]);
	printf("长度为%d\n", len);
	sem_init(&sem, 0, 0);
	struct filedata file1;
	strcpy(file1.fileread, argv[1]);
	strcpy(file1.filewrite, argv[2]);
	file1.len = len;


	pthread_t tid1, tid2;
	if(pthread_create(&tid1, NULL, task1, &file1)!=0)
	{
		printf("线程创建失败\n");
		return -1;
	}
	
	if(pthread_create(&tid2, NULL, task2, &file1)!=0)
	{
		printf("线程创建失败\n");
		return -1;
	}

	pthread_join(tid1, NULL);
	pthread_join(tid2, NULL);

	printf("回收完毕！");
	sem_destroy(&sem);

	return 0;
}