Comment 5 for bug 978356

squid3 includes a resolvconf script to run whenever DNS servers change:

#!/bin/sh

PATH="/usr/sbin:/usr/bin:/sbin:/bin"

# Make squid aware of changes to resolv.conf
if status squid3 | grep "start/running" > /dev/null; then
 reload squid3
fi

reconfigure also ends a HUP:

            if (!strncmp(optarg, "reconfigure", strlen(optarg)))
                /** \li On reconfigure send SIGHUP. */
                opt_send_signal = SIGHUP;

And yes, thats what I mean, there's a lag between when squid might receive the HUP, and when it will handle it properly. I'd rather ignore that HUP than die, since most of what it is doing at that exact time is reading its configuration and then attempting DNS lookups. I haven't looked deep enough into the code yet to see if it could handle the full reconfiguration earlier.