The libpvm library
has a tracing system
that can record the parameters and results of all calls to interface
functions.
Trace data is sent as messages to a trace sink task
just as output is sent to an stdout sink (Section 
).
If the trace output TID is set to zero (the default),
tracing is disabled.
Besides the trace sink, tasks also inherit a trace mask, used to enable tracing function-by-function. The mask is passed as a (printable) string in environment variable PVMTMASK. A task can manipulate its own trace mask or the one to be inherited from it. A task's trace mask can also be set asynchronously with a TC_SETTMASK control message.
Constants related to trace messages are defined in public header file pvmtev.h. Trace data from a task is collected in a manner similar to the output redirection discussed above. Like the type Spawn, Begin, and End messages which bracket output from a task, TEV_SPNTASK, TEV_NEWTASK and TEV_ENDTASK trace messages are generated by the pvmds to bracket trace messages.
The tracing system was introduced in version 3.3 and is still expected to change somewhat.