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On 24 Dec 2003 11:25:04 -0500, Jim Blandy <jimb@xxxxxxxxxx> wrote:
So, to invoke a C function that might perform callbacks, you must collect and pop your nursery, to allow you to place that call's frame at the (now exposed) younger end of the C frame area. In contrast, to call a C function that you know will not perform callbacks, none of that is necessary; you just make the call on top of whatever nursery you've got.
It seems to me that the called function also must not allocate any heap objects. Or do you simply allocate them directly in the next older generation, bypassing the nursery altogether?
Yes, that's a possibility. The space needed for result values is currently pre-allocated and passed to the code that wraps the called function. Callbacks into Scheme can of course allocate as much as they like, since on return from the callback, live data is moved into the next generation again. cheers, felix