Squid internal overview

Squid main loop - src/main.c
After setup, squid does two things in the main loop
Run the next event or events which are ready -eventRun()
Handle pending network and disk IO - comm_select()

main()
{
    /* Various setup tasks */
    for (;;) {
        /* Check for reconfiguration, log rotation, or shutdown */
        eventRun();			/* Run next events */
        loop_delay = eventNextTime();	/* Get the time to next event */
        comm_select(loop_delay);	/* Wait for network IO */
    }
}