2/27作业

1.若没有子进程 waitpid函数能否运行成功

#include <stdio.h> 
#include <unistd.h>  
#include <sys/types.h> 
#include <sys/stat.h>  
#include <fcntl.h> 
#include <string.h>
#include <sys/wait.h>
#include <stdlib.h>
int main(int argc, const char *argv[])
{
	pid_t cpid=fork();
	int ex_cpid=0;

	if(cpid>0)
	{
		printf("this is parent\n");
		while(1)
		{
			printf("parent:%d child:%d %d\n",getpid(),cpid,__LINE__);
			ex_cpid=waitpid(-1,NULL,WNOHANG);
			printf("excpid=%d\n",ex_cpid);
			sleep(1);
		}
	}
	else if(0==cpid)
	{
	    printf("this is child\n");
		int i=0;
		while(i<2)
		{
			printf("------\n");
			sleep(1);
			i++;
		}	
		printf("child process is ready to exit\n");
		exit(1);
	}
	else if(cpid<0)
	{
		perror("fork");
		return -1;
	}
	while(1)
		sleep(1);
	return 0;
}

当没有子进程时，函数会运行失败。

2.waitpid能否回收兄弟进程

#include <stdio.h> 
#include <unistd.h>  
#include <sys/types.h> 
#include <sys/stat.h>  
#include <fcntl.h> 
#include <string.h>
#include <sys/wait.h>
#include <stdlib.h>
int main(int argc, const char *argv[])
{
	pid_t cpid=fork();//子1
	int ex_cpid=0;

	if(cpid>0)
	{
		printf("this is parent\n");	
		if(fork()==0)//子2
		{
			printf("子2\n");
			printf("ex_cpid=%d\n",waitpid(cpid,NULL,0));
			printf("子2退出\n");
			return 0;
		}

		while(1)
		{
			printf("parent:%d child:%d %d\n",getpid(),cpid,__LINE__);
			sleep(1);
		}
	}
	else if(0==cpid)
	{
	    printf("this is child\n");
		int i=0;
		while(i<2)
		{
			printf("------\n");
			sleep(1);
			i++;
		}	
		printf("child process is ready to exit\n");
		exit(1);
	}
	else if(cpid<0)
	{
		perror("fork");
		return -1;
	}
	while(1)
		sleep(1);
	return 0;
}

兄弟进程间无法相互回收

3. waitpid子进程能否回收父进程

#include <stdio.h> 
#include <unistd.h>  
#include <sys/types.h> 
#include <sys/stat.h>  
#include <fcntl.h> 
#include <string.h>
#include <sys/wait.h>
#include <stdlib.h>
int main(int argc, const char *argv[])
{
	pid_t cpid=fork();
	int ex_cpid=0;

	if(cpid>0)
	{
		printf("this is parent\n");
		while(1)
		{
			printf("parent:%d child:%d %d\n",getpid(),cpid,__LINE__);
			exit(0);
			sleep(1);
		}
	}
	else if(0==cpid)
	{
		printf("this is child\n");
		ex_cpid=waitpid(getppid(),NULL,0);
		printf("excpid=%d\n",ex_cpid);
		int i=0;
		while(i<2)
		{
			printf("------\n");
			sleep(1);
			i++;
		}	
		printf("child process is ready to exit\n");
		exit(1);
	}
	else if(cpid<0)
	{
		perror("fork");
		return -1;
	}
	while(1)
		sleep(1);
	return 0;
}

子进程无法回收父进程资源。

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