Precision with "setrlimit"

[Maybe Lau]

Hello everyone, I'm new here. I'm a Chinese high school student. I hope you
can help me.
When I tried to use setrlimit to limit CPU time of a process, I was in
trouble. My code is like this:

int new_limit_process( char *exec , int time )
{
pid_t ret;

ret = fork();
if ( ret == -1 )
perror( "fork" );
if ( !ret )
{
struct rlimit lim;

if ( time != LIM_INF )
{
lim.rlim_max = lim.rlim_cur = time;
if ( setrlimit( RLIMIT_CPU , &lim ) == -1 )
perror( "setrlimit cpu" );
}

if ( execlp( exec , exec , NULL ) == -1 )
perror( "execlp" );
}
return ret;
}

But when I limited a process's CPU time to 10 sec, it was killed after more
than 1 min. I don't know if it's right with my code and if it's right with
the status.
I'm developing a online application that can use in NOIP, a contest like the
ACM-ICPC, for our school. So I need a high precision.
What's the problem with my code? Or what should I do?

I'm using Ubuntu 11.04 with linux kernel 2.6.38-8-generic.

P.S. I'm not good at English. Sorry for my mistakes if there are.
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