On 9 June 2015 at 20:05, Matthieu Lacaton <matthieu.laca...@gmail.com>
wrote:
> *@ Igor*
>
>
>> As i understand, in general, the problem that you described is in
>> following:
>> - you want to pass an address of your buffer contents, but started not
>> from
>> very first element of your buffer, but somewhere inside a buffer.
>
>
> Yes ! Exactly that. I'm bad at explaining things :(
>
> me too, sometimes. :)
>
> Unfortunately, this is the only way how we could implement such, lets say
>> 'ElementPointer' safely. Which then can be used to pass to C function(s),
>> converting object reference + offset into simple address just before
>> invoking a function (and sure thing, knowing that there's no chance
>> triggering GC, else it will turn into pointer to wrong place, but that's
>> general problem of passing pointers on object memory heap, not just
>> exclusively for 'element pointer' and such).
>>
>
> Alright, thank you very much for your explanations ! By the way, is there
> a way to disable the GC for a short period of time and then re-enable it ?
>
> Well, some aspects of GC behavior can be controlled, but they serve rather
for fine tuning or picking the strategy ahead of time, knowing, what
application is going to run. So, at application level, you can use them..
but not at the level of library/framework (like in case of NB), because
there's no way to determine what/where will be used, and so, fiddling with
GC is worst possible way to solve the problem :)
Also, in general, it would be a bad practice to rely on subtle and fuzzy
details of GC triggering logic, because it is one of the most sophisticated
parts of VM and subject of future changes.
So, instead relying on implementation details, a new contract between VM
and language side is introduced and it called 'object pinning'. So, that
pinned objects are no longer a subject of relocation in memory. It means
that you will be able to control, that chosen object(s) will be not
relocated in memory, regardless how often VM triggers GC and what is
involved.
And that comes with Spur.
>
> *@ Henrik*
>
> I am not sure I understand every bit of your code right now but I will
> definitely study it because it looks awesome.
> Moreover, performance is quite important for me so your solution is very
> attractive and I'll try to use it. Thanks a lot !
>
> I find it both fun and amazing what you can do with Pharo. I never thought
> I would do assembly inside Pharo !
>
>
> Again, a big thanks to both of you,
>
> Cheers,
> Matthieu
>
>
>
>
> 2015-06-09 17:43 GMT+02:00 Igor Stasenko <siguc...@gmail.com>:
>
>> As i understand, in general, the problem that you described is in
>> following:
>> - you want to pass an address of your buffer contents, but started not
>> from
>> very first element of your buffer, but somewhere inside a buffer.
>>
>> In smalltalk you cannot reference an element of array,
>> only the object (array in that case) as a whole.
>>
>> The reason why it like so, because VM moves objects around, and you
>> cannot control directly when that happens,
>> and also VM responsible for updating all pointers (references) to moved
>> object(s)
>> for all interested parties (which could be other objects, stack etc) ,
>> making sure all references remain consistent upon such move.
>> So, with such constraints, the only way to validly point to an element
>> inside array
>> would be to store two values separately:
>> - a reference to an object, that represent your buffer (which VM would
>> update at will)
>> - an index (or offset) in that object, pointing to element in your buffer
>>
>> Unfortunately, this is the only way how we could implement such, lets say
>> 'ElementPointer' safely. Which then can be used to pass to C function(s),
>> converting object reference + offset into simple address just before
>> invoking a function (and sure thing, knowing that there's no chance
>> triggering GC, else it will turn into pointer to wrong place, but that's
>> general problem of passing pointers on object memory heap, not just
>> exclusively for 'element pointer' and such).
>>
>> For buffers allocated externally, e.g. outside heap governed by VM,
>> there's nothing prevents you from having an address that pointing inside
>> some buffer (or even outside it :)
>>
>> For NBExternalAddress:
>>
>> addr := self allocate: somespace.
>>
>> newAddr := NBExternalAddress value: addr value + someoffset.
>>
>> or
>>
>> newAddr := addr copy value: addr value + someoffset
>>
>> sure, it is up to you then, how to calculate offsets and buffer size(s)
>> as well as allocating/deallocating memory for buffers you using.
>>
>>
>> On 8 June 2015 at 16:41, Matthieu Lacaton <matthieu.laca...@gmail.com>
>> wrote:
>>
>>> Hello everyone,
>>>
>>> I have a small question about NativeBoost : How does the "+" operator
>>> when applied to a pointer translates into NativeBoost code ?
>>>
>>> To give a bit of context, what I want to do is to reallocate some
>>> non-contiguous bytes in memory to a buffer. Basically, I have an array of
>>> integers in a buffer and I want to copy some chunks of it in another
>>> buffer. The chunks are always the same size and the offset between each
>>> chunk is always the same too.
>>>
>>> Because a bit of actual code is easier to understand here is what I'd
>>> like to do in Pharo :
>>>
>>> ...
>>>
>>> int i, j;
>>> int *data = malloc(1000*sizeof(int));
>>> int *newData = malloc(50*sizeof(int));
>>>
>>> // Allocate initial data
>>> for (i = 0 ; i < 1000, i++) {
>>> data[i] = i;
>>> }
>>>
>>> //Copy desired chunks into new buffer
>>> for (i = 0; i < 5; i++ ) {
>>> memcpy( newData + j*10, data + 200 + j*30, 10*sizeof(int));
>>> j++;
>>> }
>>>
>>> free(data);
>>>
>>> ...
>>>
>>> Here basically I'll get in my buffer chunks of 10 integers starting at
>>> 200 with an offset of 30 between chunks, and this 5 times. (200 201 202 ...
>>> 208 209 230 231 ... 238 239 260 ... 328 329).
>>>
>>> I am okay with the malloc, memcpy and free but I don't know how to
>>> handle the "+" operator in my memcpy function.
>>>
>>> Thank you,
>>>
>>> Matthieu
>>>
>>
>>
>>
>> --
>> Best regards,
>> Igor Stasenko.
>>
>
>
--
Best regards,
Igor Stasenko.
