Exception Handling

Sun Jun 13 12:33:00 GMT 2004

Chris Gray writes:
 > 
 > > > The number of stack frames which have to be unwound is probably
 > > > also of interest: my guess would be that many throws are caught in
 > > > the same stack frame, but a substantial number will propagate a
 > > > long way up the stack.
 > > >
 > > > I think the measurements will have to be done by instrumenting the
 > > > compiler - it's not easy for a runtime such as IKVM (or Wonka) to
 > > > know that a try{} block is being entered. IOW I'm not volunteering
 > > > to make the measurements, just suggesting that Somebody should do
 > > > something. :)
 > >
 > > Well, I can do it easily, but then I have to have a corpus of code to
 > > measure. And some reason to do the study at all: unless there is a
 > > realistic prospect of defining a new unwinder mechanism, there will be
 > > little point.
 > 
 > Yes of course there has to be an a priori case to answer, and some
 > likelihood that if the try/throw ratio proves to be low then some
 > effort to define a new unwinding mechanism will be made. That's
 > optimisation for you: guess, measure, experiment, repeat.
Yeah, but we can't change the mechanism used by gcj because we use the
same mechanism as C++, and this is defined by the ABI of the platforms
we run on. It may be that the ratio of try/throw is different in Java
programs and C++ programs, of course, so we may suffer because we use
the same mechanism.
Andrew.