2023.05.06 IO进程线程DAY5

1.使用文件IO函数，拷贝一张图片，父进程拷贝前半部分，子进程拷贝后半部分。不能使用sleep函数。

#include 
#include 
#include 
#include 
#include 

int main(int argc, const char *argv[])
{
	int fd_r = open("./1.png", O_RDONLY);
	if(fd_r < 0)
	{
		perror("open");
		return -1;
	}
	int fd_w = open("./copy.png", O_WRONLY | O_CREAT | O_TRUNC, 0755);
	if(fd_w < 0)
	{
		perror("open");
		return -1;
	}
	
	off_t filesize = lseek(fd_r, 0 ,SEEK_END); //计算文件大小
	lseek(fd_r, 0, SEEK_SET);                  //重新偏移到开头
	char c = 0;
	long i = 0;
	while(i < filesize/2)
	{
		read(fd_r, &c, 1);
		write(fd_w, &c, 1);
		i++;
	}

	pid_t cpid = fork();
	if(cpid == 0)
	{
		while(1)
		{
			ssize_t res = read(fd_r, &c, 1);
			if(res == 0)
				break;
			write(fd_w, &c ,1);
		}
	}
	else if(cpid == -1)
	{
		perror("fork");
		return -1;
	}


	return 0;
}

2.父进程以非阻塞形式运行到waitpid时，若子进程没退出，则子进程会不会变成僵尸进程

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 


int main(int argc, const char *argv[])
{
	pid_t cpid = fork();

	if(cpid > 0)
	{
		printf("parent pid=%d\n",getpid());
		int wstatus = 0;
		waitpid(-1, &wstatus, WNOHANG);
		//waitpid(-1, &wstatus, 0);
		printf("%d\n", (wstatus&0xff00)>>8);

	}
	else if(cpid == 0)
	{
		printf("child pid=%d\n",getpid());
		sleep(5);
		printf("子进程准备退出\n");
		exit(0);
	}
	else
	{
		perror("fork");
		return -1;
	}

	while(1)
		sleep(1);
	return 0;
}

子进程会变成僵尸进程；

3.创建孤儿进程和僵尸进程

孤儿进程：父进程退出，子进程还在运行

#include 
#include 
#include 
#include 
#include 
#include 
#include 


int main(int argc, const char *argv[])
{
	pid_t cpid = fork();

	if(cpid > 0)
	{
		printf("父进程 pid=%d\n", getpid());
		exit(0);
	}
	else if(cpid == 0)
	{
		sleep(1);
		printf("子进程 pid=%d ppid=%d\n", getpid(), getppid());
	}
	else
	{
		perror("fork");
		return -1;
	}

	while(1)
		sleep(1);
	return 0;
}

僵尸进程：子进程退出，父进程没有收尸

#include 
#include 
#include 
#include 
#include 
#include 
#include 


int main(int argc, const char *argv[])
{
	pid_t cpid = fork();

	if(cpid > 0)
	{
		printf("parent pid=%d\n", getpid());
	}
	else if(cpid == 0)
	{
		printf("child pid=%d\n", getpid());
		exit(0);
	}
	else
	{
		perror("fork");
		return -1;
	}

	while(1)
		sleep(1);
	return 0;
}