From: Chris Uzdavinis <chris@...>
Date: 2001-07-17T03:54:26+09:00
Subject: [ruby-talk:17943] Re: RUBY C++ Extension

Sean Middleditch <elanthis@users.sourceforge.net> writes:

> On Tue, Jul 17, 2001 at 01:54:18AM +0900, Bernhard Gl?ck wrote:

> > Does anybody have the source to a WORKING C++ Class exported to
> > RUBY (preferably using MSVC 6.0) ?  I would like to instantiate my
> > C++ classes in RUBY just the way as in C++ code.  All samples and
> > docs I found are on straigt C Extensions and that does not help
> > much.
> 
> I dunno how other people do it, but I wrap the C++ calls in C
> functions.  Pass the C++ class pointer along with the Ruby object,
> cast it in the C function, and have it call the proper C++ method.

That's probably the best way to do it.  I'm finding that writing ruby
extension functions in C++ is very problematic, since when a ruby
function throws an exception, all auto (stack based) objects in the
C++ extenstion function are not cleaned up due to the longjmp.  This
situation is specifically described in the C++ standard as having
undefined behavior.

There are really only a few solutions, none are very satisfying:

1) don't create any C++ stack based objects in a C++ extension
   function, unless they do not have destructors needing to be
   invoked.  (Structures containing only data of builtin-types is the
   only ok type of local data.)

2) create a struct on the heap, and wrap that struct in a Ruby object
   that gets registered with teh garbage collector.  The data in that
   struct can serve as your "local" variables.  But you have less
   deterministic object lifetimes (since they get destroyed when the
   GC kicks in, not when they go "out of scope.")

3) Change the internals of Ruby to not use setjmp/longjmp for its
   exception handling, but to instead return some error code.  There
   is a preprocessor macro solution which can "simulate" exceptions
   like this, as is done by the ACE C++ framework (which implements
   exceptions very similar to C++ exceptions for compilers which do
   not have native C++ exceptions.)  This technique will work in C as
   well, I think.

   Of course, this chagnes just about everything in Ruby, and would
   break everything, and be a massive job.  But maybe it's a good idea
   for a future version.  (Not very practical right now, but it's
   worth thinking about.)

-- 
Chris