ircd/api/events

Overview

The IRC server is built around an event loop. Until the u2.10.11 release (which is what ircd-darenet 1.x is based off of), this event loop has been rather ad-hoc; timed events are hard-coded in, signals are handled inside the signal handler, etc. All of this changed with u2.10.11. A new subsystem, the events subsystem, was introduced; the new subsystem contains a generalization of the concept of an event. An event is a signal, the expiration of a timer, or some form of activity on a network socket. This new subsystem has the potential to vastly simplify the code that is arguably the core of any network program, and makes it much simpler to support more exotic forms of network activity monitoring than the conventional select() and poll() calls.

The primary concepts that the events subsystem works with are the "event," represented by a struct Event, and the "generator." There are three types of generators: sockets, represented by a struct Socket; signals, represented by a struct Signal; and timers, represented by struct Timer. Each of these generators will be described in turn.

Signals

The signal is perhaps the simplest generator in the entire events subsystem. Basically, instead of setting a signal handler, the function signal_add() is called, specifying a function to be called when a given signal is detected. Most importantly, that call-back function is called outside the context of a signal handler, permitting the call-back to use more exotic functions that are anathema within a signal handler, such as MyMalloc(). Once a call-back for a signal has been established, it cannot be deleted; this design decision was driven by the fact that ircd never changes its signal handlers.

Whenever a signal is received, an event of type ET_SIGNAL is generated, and that event is passed to the event call-back function specified in the signal_add() call.