Dear Marc,

Sometimes I have a Scheme u8vector - a normal ___MOVABLE one, not ___STILL - and I have some C object such as a void* malloc()ation. Right now, to move blobs between Scheme and C, I need to carry out two steps: |##still-copy| the u8vector so it becomes ___STILL, and then in a c-lambda, memcpy() the ___STILL u8vector's contents to the C void* .

Ideally this could be done in one single step, by a Gambit primitive, which both has access to the void* fixed memory address *AND* to the u8vector in accordance to its current memory location under the GC/automatic memory management.

Do you offer a procedure something like (##u8vector-copy-to-ffi-static-ptr movable-u8v ptr length) ? And also in the opposite direction, (##copy-ffi-static-ptr-to-u8vector void* length movable-u8v offset) This would save me of one cycle of actually-unnecessary copying.

Motivation: when I pass a u8vector as scheme-object into the FFI as ___SCMOBJ, that ___SCMOBJ can be invalidated in any moment by Gambit's GC/memory management and for this reason I can only work with ___STILL objects in C. A Gambit primitive is not subject to this limitation and therefore would help circumvent this problem.

Best regards, Phil

On Mon, Oct 12, 2020 at 10:30 AM Phillip Suero philsuero@gmail.com wrote:

Dear Marc,

I see in https://github.com/gambit/gambit/blob/master/lib/mem.c#L1621-L1636 that actually ___alloc_scmobj is a wrapper for ___alloc_scmobj_still, great that clarifies that aspect.

Just curious, when ___ps == NULL it has custom behavior (specifically it will wrap to ___alloc_scmobj_perm instead). In what situation would ___ps ever be NULL?

Thanks, Phil

On Mon, Oct 12, 2020 at 10:01 AM Phillip Suero philsuero@gmail.com wrote:

...

Dear Marc,

I am sending over an u8vector from the Scheme world to the C world. Of course the u8vector must be still, so that its heap allocated object's memory address is not moved by Gambit's memory system. To get clear on this topic, I have three quick questions for you:

(1) I see there's the function |##still-copy| in Gambit's runtime. Browsing its code I don't see the keyword ___STILL mentioned anywhere in it. How does it get the ___STILL property, is that an implicit argument to ___alloc_scmobj ?

(2) Is |##still-copy| a "universal copier" of any heap allocated object, into an equivalent of itself that is ___STILL, so I can use it for, say, u32vector, floating point number, complex number, string, Scheme struct?

(3) Is there any checker in Gambit's runtime, e.g. a |##still?|, whereby I can check if a heap allocated object is ___STILL already?

Your clarification is much appreciated, thanks! Phil