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Date: Thu, 26 Jul 2001 01:48:24 -0700
From: Chris Hecker <checker@d6.com>
Subject: [Caml-list] register_global_root, malloc, etc.
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Say I've got the following C struct:

struct foo
{
	int something;
	value callback;
};

If I'm writing a module in C and want to have an abstract type that corresponds to that struct (allocated with new/malloc/etc. from C), is the following code correct?

CAMLlocal1(result);
foo *p = new foo;
p->callback = Val_unit;
register_global_root(&(p->callback));
result = alloc_small(1,Abstract_tag);
Field(result,0) = (value)p;
CAMLreturn(result);

Then, later, I can just assign another closure passed to a C function (and CAMLparam'ed) to p->callback without worrying about it, like this:

value set_callback( value fooval, value callback )
{
	CAMLparam2(fooval,callback);
	foo *p = (foo *)Field(fooval,0);
	p->callback = callback;
	CAMLreturn(Val_unit);
}

Is that correct?  Should I use Custom_tag and register all the finalization functions and whatnot for my abstract type, or is Abstract_tag good enough assuming I've got a free_foo function that users of the module are supposed to call to deallocate the abstract type?  free_foo should call remove_global_root before deleting the memory, right?  But I don't need to do anything to explicitly delete the callback or the Abstract_tag block that was passed in since the GC will handle it?

Thanks,
Chris

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