利田小子

/*
 * exercise8-7.c
 *
 *  Created on: Nov 11, 2011
 *      Author: zhuhuang
 */
 
 
#include <stdio.h>
#include <unistd.h>
#include <dirent.h>
#include <fcntl.h>
 
int main(void)
{
	DIR *dir;
	int filedes1, filedes2;
	int fdflag1, fdflag2;
	struct dirent *direntry;
 
	filedes1 = open("/", O_RDONLY);
 
	//file descriptor flag before calling opendir. it is off.
	fdflag1 = fcntl(filedes1, F_GETFD);
	if(fdflag1 & FD_CLOEXEC)
		printf("filedes1: close-on-exec flag is onn");
	else
		printf("filedes1: close-on-exec flag is offn");
 
	//See Page 234 on APUE2e, opendir function will set the close-on-exec flag for the descriptor filedes
	dir = fdopendir(filedes1);
	while((direntry = readdir(dir)) != NULL)
	{
		printf("%sn", direntry->d_name);
	}
 
	//file descriptor flag after calling opendir. it is on now.
	fdflag1 = fcntl(filedes1, F_GETFD);
	if(fdflag1 & FD_CLOEXEC)
		printf("filedes1: close-on-exec flag is onn");
	else
		printf("filedes1: close-on-exec flag is offn");
 
	//set close-on-exec flag operation on filedes1 won't affect filedes2
	filedes2 = open("/", O_RDONLY);
	fdflag2 = fcntl(filedes2, F_GETFD);
	if(fdflag2 & FD_CLOEXEC)
		printf("filedes2: close-on-exec flag is onn");
	else
		printf("filedes2: close-on-exec flag is offn");
}

/*
 * exercise8-2.c
 *
 *  Created on: Nov 10, 2011
 *      Author: zhuhuang
 */
 
#include <apueerr.h>
 
int glob = 6;
 
int callvfork(void)
{
	int var=88;
	pid_t pid;
 
	//compare the running results using vfork and fork
 
	/* Using fork
	in main first:4656
	before callvfork
	in callvfork parent:4656
	glob: 6, var: 88
	in main second:4656
	after callvfork
	before anothercall
	in anothercall:4656
	after anothercall
	in callvfork child:4661
	in main second:4661
	after callvfork
	before anothercall
	in anothercall:4661
	after anothercall
	*/
 
	/* Using vfork
	in main first:4608
	before callvfork
	in callvfork child:4613
	in main second:4613
	after callvfork
	before anothercall
	in anothercall:4613
	after anothercall
	in callvfork parent:4608
	glob: 7, var: 2077184
	*/
 
	if((pid = fork()) < 0){
		err_sys("vfork error");
	}else if(pid == 0){
		//the increasing of the variables done by the child changes the values in the parent
		glob++;
		printf("in callvfork child:%dn", getpid());
		return 0;
	}
 
	printf("in callvfork parent:%dn", getpid());
	printf("glob: %d, var: %dn", glob, var);  //var is
}
 
int anothercall(void)
{
	int i;
	int buf[100];
 
	for(i=0;i<100;i++)
		buf[i]=1;
 
	printf("in anothercall:%dn", getpid());
}
 
int main(void)
{
	printf("in main first:%dn", getpid());
 
	printf("before callvforkn");
	callvfork();
 
	//Using vfork: child process continues to execute the following code. But parent process doesn't.
	//Using fork: both child and parent processes execute the following code.
	printf("in main second:%dn", getpid());
 
	printf("after callvforkn");
	printf("before anothercalln");
	anothercall();
	printf("after anothercalln");
 
	exit(0);
}