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Old 07-11-2009, 10:31 PM   #1
bandaru_sivakrishna
LQ Newbie
 
Registered: Jul 2009
Posts: 13

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vfork syscall


#include<stdio.h>
#include<sys/types.h>
#include<unistd.h>

void main()
{
printf("\nTEST THE FORK SYS CALL\n");
vfork();
vfork();
vfork();
printf("\nhello world\n");
}


Note: the output is "hello world" print only 2 times why?
 
Old 07-12-2009, 05:52 AM   #2
Valery Reznic
ELF Statifier author
 
Registered: Oct 2007
Posts: 676

Rep: Reputation: 137Reputation: 137
Quote:
Originally Posted by bandaru_sivakrishna View Post
#include<stdio.h>
#include<sys/types.h>
#include<unistd.h>

void main()
{
printf("\nTEST THE FORK SYS CALL\n");
vfork();
vfork();
vfork();
printf("\nhello world\n");
}


Note: the output is "hello world" print only 2 times why?
Add
Code:
exit(0)
after last printf and it will work as it should be
 
Old 07-13-2009, 06:11 PM   #3
x_terminat_or_3
Member
 
Registered: Mar 2007
Location: Plymouth, UK
Distribution: Fedora Core, RHEL, Arch
Posts: 342

Rep: Reputation: 38
shouldn't that be

Code:
_exit(0);
when inside a child?
 
Old 07-14-2009, 12:21 AM   #4
Valery Reznic
ELF Statifier author
 
Registered: Oct 2007
Posts: 676

Rep: Reputation: 137Reputation: 137
Quote:
Originally Posted by x_terminat_or_3 View Post
shouldn't that be

Code:
_exit(0);
when inside a child?
Yes and no.

After reading
http://linux.die.net/man/2/vfork

I realized that code is wrong: after vfork only exec* or _exit() allowed,
i.e behavour for
Code:
vfork()
printf()
is undefined.

So when I added exit() and it's work it was only by chance()
 
  


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