On Nov 20, 2007, at 8:10 AM, Rich Morin wrote:
> At 12:04 -0800 11/19/07, Roman Shaposhnik wrote:
>> On Thu, 2007-11-15 at 21:11 -0800, Rich Morin wrote:
>>> A couple of providers have been proposed here, and I know that
>>> Apple has added providers for Python and Ruby. So, I wonder
>>> what kind(s) of plugin APIs may exist for DTrace. Is there,
>>> for example, something like a REST-based interface that some
>>> arbitrary script could feed?
>>
>> I'm not sure I understand what kind of "plug-ins" you are
>> talking about. Care to elaborate?
>
> The fact that both Sun and Apple have added providers tells us
> that there are ways to do so. The question is whether these
> ways are open to (say) a Perl scripter or the fellow who wants
> to instrument Erlang programs.
>
> At this point, I suspect that the answer is no, but it doesn't
> hurt to speculate. So, here's a bit of Science Fiction:
>
> Sitting in a Perl script, I make calls to dtrace_event(),
> handing it some data structures and flags. If a probe has
> been set for this event (i.e., for the flags I've enclosed),
> the information is passed on to dtrace to trigger the probe.
>
> In the probe's associated D code, I reach into the data
> structures, pull out the information I want to log, store
> to control other logging activities, etc.
>
> The idea here is to allow arbitrary programs to voluntarily
> submit information to dtrace. I realize that there would be
> performance limitations to any such scheme, but the ability to
> mix in volunteered information could still be useful.
>
Sure - anyone could write such a thing. I wrote something similar in
the Ruby DTrace probes (which Apple has included). In the original
patch up on the Joyent site the added Ruby module was called Tracer
but Apple changed it to DTracer because Ruby already has a Tracer
module. Firing an event from Ruby code fires a probe called 'ruby-
probe', so it works like this:
def foo
DTracer.fire('foo-start', 'some arbitrary string')
# do work
DTracer.fire('foo-end', 'some arbitrary string')
end
And the D would look something like:
ruby*:::ruby-probe
/copyinstr(arg0) == "foo-start"/
{
printf("%s\n", copyinstr(arg1));
}
And so forth. Passing simple strings back is all I needed so
anything more complex is left as an exercise, but you get the idea.
The patch Apple ultimately included in Ruby is at http://
www.opensource.apple.com/darwinsource/10.5/ruby-67/patches/
dtrace.diff if you'd like to see how it was done with the Ruby provider.
-Scott
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