2008-01-21 08:48:23

by Li Xiaodong

Subject: [HELP]Problem with exit(0) and _exit(0) on RHEL x86

I thought the effects of exit(0) and _exit(0) should be different.

----
int main(void)
{
int var = 0;
pid_t pid;

printf("before vfork\n");
if ( (pid = vfork()) < 0 )
printf("error\n");
else if ( pid == 0 )
{
var++;
exit(0); /* Clear parent's IO */
}

printf("%d\n",var);
return 0;
}

----

int main(void)
{
int var = 0;
pid_t pid;

printf("before vfork\n");
if ( (pid = vfork()) < 0 )
printf("error\n");
else if ( pid == 0 )
{
var++;
_exit(0); /* Do not clear parent's IO */
}

printf("%d\n",var);
return 0;
}

----

But the actual results on RHEL5 x86 were beyond my ken. The outputs of the
above two are the same.

$./a.out
before vfork
1

Could anyone help me with this? Thanks.

2008-01-21 23:55:38

by Robert Hancock

Subject: Re: [HELP]Problem with exit(0) and _exit(0) on RHEL x86

Li Xiaodong wrote:
> I thought the effects of exit(0) and _exit(0) should be different.
>
> ----
> int main(void)
> {
> int var = 0;
> pid_t pid;
>
> printf("before vfork\n");
> if ( (pid = vfork()) < 0 )
> printf("error\n");
> else if ( pid == 0 )
> {
> var++;
> exit(0); /* Clear parent's IO */
> }
>
> printf("%d\n",var);
> return 0;
> }
>
> ----
>
> int main(void)
> {
> int var = 0;
> pid_t pid;
>
> printf("before vfork\n");
> if ( (pid = vfork()) < 0 )
> printf("error\n");
> else if ( pid == 0 )
> {
> var++;
> _exit(0); /* Do not clear parent's IO */
> }
>
> printf("%d\n",var);
> return 0;
> }
>
> ----
>
> But the actual results on RHEL5 x86 were beyond my ken. The outputs of the
> above two are the same.
>
> $./a.out
> before vfork
> 1
>
> Could anyone help me with this? Thanks.

Why do you expect a different result? Also, calling exit from a vforked
child is explicitly not allowed. The only things you can do are execve
or _exit.

--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from [email protected]
Home Page: http://www.roberthancock.com/