Why is stopping (or restarting) squid3 on GNU/Linux is so slow?

I'm using Ubuntu 11.04 and when calling "/etc/init.d/squid3 restart", it spends about half a minute to restart. What is it doing?

The output looks like this:

* Restarting Squid HTTP Proxy 3.x squid3*  Waiting...* ...* ...* ...* ...* ...* ...                                                                   [ OK ]* Creating Squid HTTP Proxy 3.x cache structure