[Unbound-users] error when threading enabled on local_unbound on FreeBSD 10.x

[unbound at fongaboo.com]

I was setting up local_unbound (the built-in instance of unbound in 
FreeBSD 10.x). However, I had a conf file that I had a much more 
customized from a previous install of the stock unbound I had on earlier box.

When I tried to transplant the more elaborate conf and have local_unbound 
run it, I got the following errors:

> [1437336832] unbound[69115:0] warning: too many file descriptors requested. The builtin mini-event cannot handle more than 1024. Config for less fds or compile with libevent
> [1437336832] unbound[69115:0] warning: continuing with less udp ports: 211
> [1437336832] unbound[69115:0] debug: switching log to syslog

I bit-by-bit added on section at a time to unbound.conf until I found the 
offender was this entry:

   # number of threads to create. 1 disables threading. This should equal the number
   # of CPU cores in the machine. Our example machine has 4 CPU cores.
   num-threads: 4

Why would threading cause these errors? What is the default setting when 
the entry is commented out?


TIA


  -------------------------------------------------------------------------
  shot through the heart              ooh baby do you know what that's worth
  and you're to blame                         ooh heaven is a place on earth
  darling you give love                  they say in heaven love comes first
  a bad name                              we'll make heaven a place on earth
  ORBITAL                                                     "Halcyon Live"