[racket] ffi, unioun, string: is this correct?

 > Allocate `giarg' with `(malloc 'nonatomic ...)` and never install a
   non-pointer value into it.

When I allocate giarg, I don't know yet, what type it will store. It is _union...

> Allocate the string's memory with `(malloc 'atomic-interior ...)`

So it should be something like (struct giarg (ptr string-ptr)). And I should set giarg-string-ptr whenever I ptr-set! giarg-ptr _string.
I think, it is best option.

Thank you!


Воскресенье,  1 сентября 2013, 11:10 -06:00 от Matthew Flatt <mflatt at cs.utah.edu>:
>You're right --- the string can be GC'ed at any time.
>
>There are a few ways to solve the problem:
>
> * Allocate `giarg' with `(malloc 'nonatomic ...)` and never install a
>   non-pointer value into it.
>
> * Allocate the string's memory with `(malloc 'atomic-interior ...)`
>   and arrange for that memory to be referenced from some GC-visible
>   place for as long as it can be referenced by `giarg`.
>
> * Allocate the string's memory with `(malloc 'raw ...)` and explicitly
>   `free` it when `giarg` is no longer used.
>
>At Sun, 01 Sep 2013 17:38:26 +0400, Roman Klochkov wrote:
>>  (define _giarg (_union _bool _int8 _uint8 _int16 _uint16
>>                        _int32 _uint32 _int64 _uint64
>>                        _float _double _long _ulong _pointer _string))
>> 
>> (define giarg (malloc _giarg)) (ptr-set! giarg _string "Test string")
>> 
>> ---
>> 
>> It works. But I'm afraid, that string maybe allocated temporary and will be 
>> GC'ed at any time. Or _union keep _string pointer inside?
>


-- 
Roman Klochkov
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