From: Tobias Peters <tpeters@...>
Date: 2003-04-16T21:31:40+09:00
Subject: Re: tutorial on embedding ruby (review)

On 15 Apr 2003, Steve Hart wrote:
> OK Here is an example
> 
> main()
> {
> 	ruby_init();
> 	etc
> 
> 	test()
> 	rb_gc();
> }
> 
> void test()
> {
> 	VALUE v = create me a ruby obj i dont care how
> }
> 
> So what happens to v?

v is a C variable on the stack and is of course removed when test() 
returns.

I think you rather wanted to ask: "What happens to the ruby object pointed 
to by v?"

Basically, 2 things happen:
1) When test returns, this object becomes _inaccessible_ for your code, 
since there is no VALUE left that points to it.
2) The rb_gc() call will most likely delete the object (but no 100% 
guarantee for that) (this uncertainty is caused by ruby's GC algorithm, 
not by uncertainty of my mind)

You should now answer the question: Why would you want the object to stay 
in memory after you lost any means of accessing it?

> 
> or
> 
> main()
> {
> 
> 	VALUE 	v;
> 
> 	ruby_init();
> 	etc
> 
> 	test(&v)
> 	rb_gc();
> 
> 	do some stuff that uses v
> }
> 
> void test(
> VALUE *v)
> {
> 	*v = create me a ruby obj i dont care how
> }

After looking at ruby_init() and Init_stack(), I can tell that you've
really found a problem here. But if you rewrite it as

> main()
> {
> 	ruby_init();
        do_stuff()
> }
  do_stuff()
> {
> 	VALUE 	v;
>
> 	etc
> 
> 	test(&v)
> 	rb_gc();
> 
> 	do some stuff that uses v
> }

it will work fine and not delete the ruby object as long as v is on the 
stack 

   T