DHCP threaded operations

The last piece of the DHCP server is actually a set of operations that are used to keep things running. Because the DHCP server is threaded, these operations are actually set up as threads that occasionally do things to make sure everything is together.

The first thread, the main thread, handles the SRC requests (such as startsrc, stopsrc, lssrc, traceson, and refresh). This thread also coordinates all operations that affect all threads and handles signals. For example,

• A SIGHUP (-1) causes a refresh of all databases in the configuration file.
• A SIGTERM (-15) will cause the server to gracefully stop.

The next thread, the dadmin thread, interfaces with dadmin client program and the DHCP server. The dadmin tool can be used to get status as well as modify the database to avoid editing the database files manually. Previous versions of the DHCP server prevented any clients from getting addresses if a status request was running. With the addition of the dadmin and src threads, the server can handle service requests and still handle client requests.

The next thread is the garbage thread, which runs timers that periodically clean the database, save the database, purge clients that do not have addresses, and remove reserved addresses that have been in reserve state for too long. All these timers are configurable (see DHCP configuration). The other threads are packet processors. The number of these is configurable; the default is 10. Each of these can handle a request from a DHCP client. The number of packet processors required is somewhat load- and machine-dependent. If the machine is used for other services than DHCP, it is not wise to start up 500 threads.