DTrace: Sending ^C while running script produces no output

[Brandon Gooch]

I've been tinkering with DTrace a bit, and I've notice something
peculiar on each system I've tried it on.

Sending ^C from the keyboard in the terminal (console, XTerm, Konsole)
produces no output [1].

For example, while trying out a one-liner (from
http://www.brendangregg.com/DTrace/dtrace_oneliners.txt):

brandon at d820:~$ sudo dtrace -n 'syscall:::entry { @num[execname] = count(); }'
dtrace: description 'syscall:::entry ' matched 514 probes
^C

brandon at d820:~$                                                   (12-02 23:11)


If I instead, from another terminal, use pkill to quit or terminate
the process, I get output:

brandon at d820:~$ sudo dtrace -n 'syscall:::entry { @num[execname] = count(); }';
dtrace: description 'syscall:::entry ' matched 514 probes


  akonadi_control                                                   4
  akonadiserver                                                     5
  syslogd                                                           6
  sendmail                                                          8
  akonadi_ical_resour                                              12
  akonadi_maildir_res                                              12
  akonadi_nepomuk_con                                              12
  akonadi_vcard_resou                                              12
  kuiserver                                                        12
  akonadi_maildispatc                                              14
  korgac                                                           14
  virtuoso-t                                                       15
  dbus-daemon                                                      17
  mysqld                                                           18
  hald                                                             24
  knotify4                                                         27
  akonadi_contacts_re                                              36
  nepomukservicestub                                               70
  pkill                                                            70
  powerd                                                           72
  dtrace                                                          101
  zsh                                                             111
  sudo                                                            495
  kwin                                                           2812
  firefox-bin                                                    3175
  kdeinit4                                                      11044
  Xorg                                                          39588
brandon at d820:~$                                                   (12-02 23:14)


I also want to add that I've tried this with a variety of shells on
both 8.2-PRERELEASE and HEAD systems, i386 and amd64, built with GCC
and nearly GENERIC kernels in order to try to eliminate the cause.

I feel as though this has something to do with file descriptors being
closed too soon when handling the signal or something of that nature.
It's also been suggested that this could be a bug in libdtrace, but I
haven't the knowledge (or skill) to try and pinpoint the cause myself.

Is there anyone here that may be able to provide feedback or debugging
suggestions?

Thanks!

-Brandon

[1] This isn't always the case, only like 99.99% of the time.
Sometimes I do get output, but usually it's just snippets, and
sometimes random characters!