2010/1/5 vagy <vagy at freemail.gr>:
> Igor Stasenko wrote:
>>
>> The difference between FloatArray and Array of floats (or array of
>> arbitrary objects)
>> is in storage format. While first storing a number of native
>> floating-point values, edigible for C,
>> while second stores references to other objects (oop-s).
>
> Indeed and this means that we can change values in C land when they
> are contained in said Arrays (ByteArray, FloatArray, IntegerArray, etc)
> but not when sent down as single values, which strikes me as kinda
> inconsistent, at least from an FFI usage point of view.
> A bit OT, speaking of FloatArray, it changes the Floats you put into it
> into single precision. So currently it is impossible to pass to C an array
> of double precision Floats. Shouldn't the image also have a DoubleArray for
> that purpose?
>
if you want to modify the floats 'in-place' - pass a pointer to it.
or pass a pointer to array and index.

>>> Another thing that isn't clear to me is if its possible to have FFI
>>> create
>>> Smalltalk objects
>>> in behalf of a requesting client. In Java's JNI for instance one can say:
>>>
>>>  jni->NewFloatArray(length of the array);
>
>
>> in that case, i think, you'd better create a VM plugin, which having
>> an access to something similar to 'jni'
>> object, which in squeak is called 'interpreterProxy'.
>
> If i understood correctly, writing a plugin with the sole purpose
> of giving access to interpreterProxy seems overkill. I would like to
> have this as standard functionality provided by FFI (and i am willing
> to implement it if you (guys) see it as valuable.
> If on the other hand you meant writing a plugin and completely bypassing
> FFI, i would rather not do it until i exhaust all possibilities with FFI
> because, modulo the issues we are talking about here, it serves my needs
> excellently.
>
FFI meant to communicate with C world, which knows nothing about Squak
VM machinery.
You seem wanting something in between the full pledged VM plugin and
arbitrary dynamic library,
which has no obligations to know anything about squeak.

>> Thinking about it, i came to interesting idea, that really, we could
>> pass a pointer to interpreterProxy
>> variable to FFI function, so, potentially, it could make use of VM API
>> functions to create objects, or access existing ones.
>
> Yeap, plus have a bunch of utility routines for creating arrays.
> There is some code in FFI thats along those lines, FFI can create
> Strings (because it knows how to copy the data from a null terminated
> C char array, see ffiReturnCStringFrom).
> Symmetrically, we can extend FFI to create Arrays of all possible basic
> types for us, let the client fill those appropriately, and then let
> FFI return the oop up to the image as usual.

FFI supports external data buffers. So you could allocate them, and
exchange the data between your module and
squeak world using pointers to these buffers. And sure thing, you can
any use data format(s) for buffer contents.
So, then when your C routine is done, you can extract the data from it
and convert them into appropriate object(s).

>
>> I don't know if that will be ever used, since writing a plugin looks
>> much more appropriate in that case.
>
> In my scenarios it would be useful, hopefully its generally useful :-)
>
> To sum up my thoughts/propositions:
>  - extend FFI with a bunch of functions that create Arrays of predefined
> size
>   of all possible C types
>  - extend FFI to provide access to the VM (via interpreterProxy) for all
>   possible unforeseen usages and needs that aren't served by FFI's existing
>   functionality
>  - (not directly FFI related) create DoubleArray object in image.
>
> I hope all these are technically feasible...
>
> Cheers
>  - Vagelis
>
>



-- 
Best regards,
Igor Stasenko AKA sig.