Profiling Isolated Sections of Code At Run Time.

Another way of controlling trace sizes is to profile only isolated sections of code. Prism supports this functionality by allowing users to turn collection on and off during program execution whenever execution is stopped - say, with a break point or by using the interrupt command.

If the profiled section will be entered and exited many times, data collection may be turned on and off automatically using tracepoints. Note that the term "trace" is used now in a different context. For TNF use, a trace is a probe. For Prism and other debuggers, a tracepoint is a point where execution stops and possibly an action takes place but, unlike a breakpoint, program execution resumes after the action.

For example, if data collection should be turned on at line 128 but then off again at line 223, one may specify

(prism all) trace at 128 {tnfcollection on}
(prism all) trace at 223 {tnfcollection off}

If the application was compiled and linked with high degrees of optimization, then specification of line numbers may be meaningless. If the application was compiled and linked without -g, then specification of line numbers will simply not work. In such cases, data collection may be turned on and off at entry points to routines using trace in routine syntax.