[dtrace-discuss] proc:::exit not firing

[Chip Bennett]

Chris,

Here's what I think might be happening.  The process specified as the -p 
argument fires the exit probe and the record of that goes in the switch 
buffer.  Then it becomes a race as to which happens first: the script 
exits because its "process of interest" exited, or the probe clause 
executes when it sees the record in the buffer.

By default, DTrace uses a switch buffer (one set per CPU).  One buffer 
is active and being written to by firing probes, while the other is 
inactive and be read from by the DTrace consumer.  By default the switch 
from active to inactive happens once a second, so the exit probe could 
be recorded a full second before the D script would get a chance to see it.

You could reduce the switch time, but that just decreases the odds of a 
mishap.  To see if this is the problem, try making the process of 
interest a regular argument rather than a "-p" argument.  Then you refer 
to it as $1 rather than $target.  That will prevent the script from 
automatically exiting when the process exits, but you could manually 
exit yourself in the last proc:::exit clause.

It's only a theory.  ;-)

Chip

Chris Debenham - RSD Engineer wrote:
> I have a funny issue whereby when a application exits the proc:::exit 
> probe doesn't seem to be firing.
> A customer has written a dtrace script that outputs some info whenever 
> proc:::exit fires but on occasion (random, no pattern in behaviour) 
> dtrace exits without outputting the data.
>
> They are running dtrace via 'dtrace -s exit_trace.d -p <pid>'
>
> Can anyone think of any reason this should be so?
>  From my reading of various documents, solaris internals and other spots 
> it appears that proc:::exit should ALWAYS be fired regardless of how the 
> process ends.
>
> Thanks
>    Chris Debenham
>
> The script they are using is as follows:
>
> --- begin script ---
> proc:::signal-send
> /args[1]->pr_pid == $target/
> {
>          last_signal = args[2];
>          last_signal_sender_pid = pid;
>          last_signal_sender_name = execname;
> }
>
> proc:::exit
> /pid == $target && args[0] == CLD_EXITED/
> {
>          printf( "%Y normal exit.", walltimestamp );
>          ustack();
> }
>
> proc:::exit
> /pid == $target && args[0] == CLD_KILLED/
> {
>          printf( "%Y exited by signal. signal=%d, sent by=%s (%d)",
>                          walltimestamp,
>                          last_signal,
>                          last_signal_sender_name,
>                          last_signal_sender_pid );
> }
>
> proc:::exit
> /pid == $target && args[0] == CLD_DUMPED/
> {
>          printf( "%Y core dump", walltimestamp );
>          ustack();
> }
>
> proc:::exit
> /pid == $target && args[0] != CLD_EXITED && args[0] != CLD_KILLED && 
> args[0] != CLD_CONTINUED && args[0] != CLD_DUMPED/
> {
>          printf( "%Y stop or cont. status = %d", walltimestamp, args[0] );
> }
>
> --- end script ---
>
>