dhcpd dup my socket?

[Water NB <netbsd78%126.com@localhost>]

I wrote a program foo, do below two steps:
1) create a pthread, listen on tcp port 38001,

# sockstat -n | grep 38001
root     foo        20060  4 tcp    *.38001               *.*

2) call system("/etc/rc.d/dhcpd restart");
# sockstat -n | grep 38001
root     dhcpd      15187  4 tcp    *.38001               *.*
root     foo        20060  4 tcp    *.38001               *.*

now:
# pkill foo
# sockstat -n | grep 38001
root     dhcpd      15187  4 tcp    *.38001               *.*

then use telnet on another machine:
$ telnet 61.144.174.157 38001
Trying 61.144.174.157...
Connected to 157.174.144.61.broad.sz.gd.dynamic.163data.com.cn.
Escape character is '^]'.


and then
# /etc/rc.d/dhcpd restart

$ telnet 61.144.174.157 38001
Trying 61.144.174.157...
telnet: Unable to connect to remote host: Connection refused



I think system("/etc/rc.d/dhcpd restart"); is the root issue.
So how to resolve it?
Thanks.