Event Callbacks

The ::evset dcmd and event tracing dcmds allow you to associate an event callback (using the -c option) with each event specifier. The event callbacks are strings that represent MDB commands to execute when the corresponding event occurs in the target. These commands are executed as if they had been typed at the command prompt. Prior to executing each callback, the dot variable is set to the value of the representative thread's program counter and the hits variable is set to the number of times this specifier has been matched, including the current match.

If the event callbacks themselves contain one or more commands to continue the target (for example, ::cont or ::step), these commands do not immediately continue the target and wait for it to stop again. Instead, inside of an event callback, the continue dcmds note that a continue operation is now pending, and then return immediately. Therefore, if multiple dcmds are included in an event callback, the step or continue dcmd should be the last command specified. Following the execution of all event callbacks, the target will immediately resume execution if all matching event callbacks requested a continue. If conflicting continue operations are requested, the operation with the highest precedence determines what type of continue will occur. The order of precedence from highest to lowest is: step, step-over (next), step-out, continue.