Squid internals

The event interface (src/event.c)
Used to schedule a non-IO triggered callback
Add an event
eventAdd(name, callback, callbackdata, when, weight)
Add an event within a random offset +-1/3 of delta_ish
eventAddIsh(name, callback, callbackdata, delta_ish, weight)
Delete a given event
eventDelete(callback, callbackdata)
Run the next event
eventRun(void)
Time until next event
time = eventNextTime(void)

How it works
eventAdd() inserts into a linked list of events after the last event with the same or earlier time
eventRun() only runs events whose callbackdata is valid (by a call to cbdataValid())
eventRun() is called in main() _before_ comm_select()