From: Matthias Lampert <ml@...>
Date: 2001-06-21T22:00:56+09:00
Subject: [ruby-talk:16702] Re: embedding C++


Hello, Chris!

Also las ich bei Chris Uzdavinis [mailto:chris@atdesk.com]
> 
> [...]
> 
> There are some important issues to remember if you're writing code by
> hand.  The biggest problem that needs to always be on your mind is
> when a Ruby exception is thrown.
> 
> Since Ruby exceptions use longjmp, the stack is not unwound like C++
> programmers expect.  Local variables will NOT have their destructors
> invoked.  Therefore you must always be very careful to protect your
> objects.  


HooaMooa!  That's an issue worth smoking 10 pipes over, indeed.  
I would have certainly been swallowed by this kind of quicksand.
Thank you for warning me!


> There are a few ways to do this.  One slowish way is to
> heap-allocate all your C++ objects and keep track of them in a global
> structure.  You can stuff these objects into Ruby objects and let the
> Ruby garbage collector take care of the memory for you if you'd like.
> (But you still need to keep track of those ruby objects somewhere so
> you can mark them for the garbage collector while you're still using
> them.) 


That's certainly the easiest solution.  By the way, Java has become
tremendously popular among coders despite or even for handling matters 
just like that.


> Another thing you can do is create local scopes around local variables
> in such a way that they always go out of scope before any ruby
> function that can possibly "throw" is called.  This is a variation of
> the design rule of "don't allow ANY stack-based variables to exist who
> need a destructor invoked to exist when you call ruby functions."

That seems to me the most performative solution, and as far as I can see,
it's also the cleanest.  


> A final way to accomplish this may be to use setjmp yourself in each
> of your C++ functions, however I have not experimented at all with
> this approach and it sounds like a high-overhead solution.

I don't know yet what calling setjmp implies. As for my own code, 
I could manipulate XEmacs to automatically produce markers in my 
methods that can be handled by some useful tool (Ruby, for 
instance) to be converted into the appropriate C++ code.  Just two
other lines in the Makefile ought to do the job in time. 

Of course, this can't easily be done on third-party code...  
And what about third-party C++ code that throws exceptions 
itself? ...
Honestly, I consider obtaining some more tobacco!

> 
> I've been thinking about writing up the issues I've encountered, but I
> still don't have a good enough solution to where I'm convinced it's
> worth writing about.
> 

That's not the issue about writing, especially not in the OS community.  
Some German success trainer said:  If you have a problem you can't solve,
tell the world that there's a problem and it WILL be solved. 

That's what I did here, and I want to thank all those who gave me all
those precious hints.

CU,

--

Hippo (aka Matthias Lampert, Hamburg)
Just another XP and Ruby fan