[Pharo-project] Status of Alien FFI

Igor Stasenko siguctua at gmail.com
Fri Sep 18 23:28:13 EDT 2009


2009/9/18 Stéphane Ducasse <stephane.ducasse at inria.fr>:
> yes this is one of my dream but ....
> I'm not good enough to make it come true.
>

Lua is specifically designed from the very starting to live well as
embedded system, written in C. No wonder that its having very good C
interoperability.
And that's why, at the time i found the smalltalk, first thing i thought, that
creating an interoperability layer between C and smalltalk will
unleash its potential
for use in scripting.
Unfortunately, almost every implementation i found & read about
smalltalk vere designed as a
self-sustained (or self-sufficient) sandboxed environment with a
little care about host interoperability in mind.
Even existence of FFI in Squeak doesn't changes that, because Squeak
VM architecture
as well as language-side design prevents you from controlling
interpreter from outside.
A less painful way for achieving a kind of embedding, as Andreas
mentioned, that you can write the
plugin which using callback machinery and create an image which simpli
'listening' for calls from outside
then handle them and put response back.
But i can't tell, how efficient it could be comparing to Lua scripting
interface.

For instance, if i would want to enable the dynamic primitive
publishing (which host application may want to
use), then this would require VM changes.
That's why i proposed , some time ago, to modify the VM internal
infrastructure to have a kind of namespace,
which is dynamically built-up using associations of symbols (C
strings) with some pointer/values.
Then you can publish primitives at any time you wanting to, replace
them at run time and do many other
kind of tricks, which is possible, when function pointer is not bound
at compile time, but discovered by VM
at run time. At some point we could even use a JIT to generate the
primitives and then let VM to pick them up at run time.
This means, that at some point you could JIT everything you need, and
replace the C-compiled VM stuff after booting the
image, and from now on, VM is not something which is made from stone
like all C-compiled binaries. So different
images could carry own system inside which, once its booted up, no
longer needs the statically compiled crap.
This also means, that by having a good JIT and VM tuned for this, we
don't really need writing any C code anymore, because
main reason why we doing this is speed and easy interoperability with
host environment. :)

> Stef
>
> On Sep 18, 2009, at 6:40 PM, Lawson English wrote:
>
>> Johan Brichau wrote:
>>> On 16 Sep 2009, at 20:37, Ken Treis wrote:
>>>
>>>
>>>> * I'm creating a partial Alien library for GemStone so that I can
>>>> use the CairoGraphics package in both Pharo and GLASS. But on
>>>> x86-64, there there's a size difference between a pointer/long and
>>>> an integer. It'd be nice to have some more explicit APIs on Alien,
>>>> so I could say "Alien newCInteger" or "Alien newCLong" and have the
>>>> platform return me the proper size Alien. Even without the platform
>>>> size differences, it seems awkward to use "Alien newC: 4" everywhere
>>>> I want an integer, "Alien newC: 8" where I want a double, etc.
>>>>
>>>
>>> Exactly.
>>>
>>> It becomes worse once you start having structs and nested structs or
>>> structs with pointers to structs ;-)
>>>
>>> I'm using Alien as the FFI to port JavaConnect from Visualworks to
>>> Pharo/Squeak. As you say, it is a pain to work at such a low-level
>>> compared to the DLLCC in VW. I am planning to do some work on
>>> creating
>>> a higher-level interface for it such that we can operate it as you
>>> mention, including the correct bytesizes for all platforms.
>>>
>>> At the moment, I'm mostly focusing on getting the port to work right
>>> before I start creating an interface on top of the current Alien
>>> interface.
>>>
>>>
>>>
>>
>> Something to keep in mind is the need for a straightforward way of
>> going
>> the other way: John Mcintosh's port of the Squeak VM to iPhone implies
>> that the same thing could be done in other Lua-ish situations,
>> allowing
>> people to use smalltalk syntax for game scripting. With the right
>> libraries for an IDE, I would think squeak could be very attractive to
>> at least some people in place of/in addition to using Lua.
>>
>>
>> Lawson
>>
>>
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>
>
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-- 
Best regards,
Igor Stasenko AKA sig.




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