Event Handlers

Event management is based on the concept of a handler. The name comes from an analogy with hardware interrupt handlers. Each event management command typically creates a handler, which consists of an event specification and a series of side-effect actions. (See Setting Event Specifications.) The event specification specifies the event that will trigger the handler.

When the event occurs and the handler is triggered, the handler evaluates the event according to any modifiers included in the event specification. (See Event Specification Modifiers.) If the event meets the conditions imposed by the modifiers, the handler’s side-effect actions are performed (that is, the handler “fires”).

An example of the association of a program event with a dbx action is setting a breakpoint on a particular line.

The most generic form of creating a handler is by using the when command.

when event-specification {action; ... }

Examples in this chapter show how you can write a command (like stop, step, or ignore) in terms of when. These examples are meant to illustrate the flexibility of the when command and the underlying handler mechanism, but they are not always exact replacements.