Re: SCM objects on the heap?

[Maciej Stachowiak <mstachow@mit.edu>]

dirk@ida.ing.tu-bs.de writes:
> Hello!
> 
> Am I right in assuming that SCM objects are only protected from gc as long
> as they are on the stack and not if they are on the heap?
> 

If SCM values are on the stack, they are autiomatically protected
against gc. If they are on the heap, they must be protected explictly,
such as with scm_protect_object()/scm_unprotect_object(). One problem
with scm_[un]protect_object for your application (and others) is that 



> example (just sketched):
> 
> SCM* p = new SCM[100];         /* C++ style, for C use malloc */
> for (unsigned int i = 0; i < 100; ++i)
>     p[i] = gh_cons(SCM_BOOL_T, SCM_BOOL_T);
> 
> If I am right, later accesses to p are not guaranteed to work with current
> guile, since the SCM objects referencing the pairs will not be detected
> during gc.
> 

Correct, unless you protect each of the slots in the array
explicitly. This is undoubtedly quite a pain in this case. Maybe Guile
could use a scm_protect_range(void *addr, size_t size) which would
conservatively protect an address range against GC until that range is
unprotected (I guess this would require a unique handle return value
to be passed to scm_unprotect_range).

 - Maciej