On Fri, 2008-01-11 at 17:32 -0800, Bryan Cantrill wrote: > On Fri, Jan 11, 2008 at 04:39:25PM -0800, Roman Shaposhnik wrote: > > On Sat, 2008-01-12 at 11:21 +1100, Sven Dowideit wrote: > > > excellent stuff Andy! > > > > > > To start with the obvious :) > > > > > > Due to the lack of ustack helper, I am hoping to add a stack probe > > > > Two things: first of all DTrace could really benefit from a > > general purpose mechanism of hooking up custom stack helpers > > with the rest of the system. Frankly, the way jstack is done > > doesn't strike me as too generic a mechanism. > > Do you actually understand how it's implemented?
Not fully, but I've spent a great deal of time staring at jhelper.d ;-) Seriously, though -- my experience comes mostly from reading the source. And the source code for DTrace can get pretty tricky. If you have any suggestion for me as to what would be a good intro into stack helpers -- I'd appreciate that. > It's actually quite > general -- witness the presence of ustack helpers for both Python and > PHP. (Indeed, the underlying mechanism is _so_ general that for some > time we weren't sure if we had fallen prey to false generality.) I guess we are talking about two different kinds of generality here. What I have in mind is the generality that would allow DTrace to be able to offload some of the heavylifting to the userspace. I DO understand the ramifications of that and I know full well that pushing DTrace into userspace might be perceived as the deviation from the original design. To some extent it might even reduce the generality that you seem to be referring to. > > Second, I would like to encourage those who do DTrace integration > > into Perl to take a look at what JavaScript is doing. They don't > > have a custom stack helper either but the set of probes they offer > > makes stack synthesis a trivial (albeit costly) matter. > > While the JavaScript approach is better than nothing, it is _not_ > preferable to the ustack approach Agreed. Still it is WAY better than nothing ;-) Thanks, Roman.
