[Vm-dev] Re: [Pharo-project] Can OSProcess functionality be implemented using FFI instead of plugin?

Igor Stasenko siguctua at gmail.com
Mon May 7 22:16:03 UTC 2012

On 7 May 2012 20:15, Eliot Miranda <eliot.miranda at gmail.com> wrote:
> On Sun, May 6, 2012 at 9:14 AM, Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com> wrote:
>> 2012/5/6 Igor Stasenko <siguctua at gmail.com>:
>> > On 6 May 2012 17:08, Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com> wrote:
>> >> 2012/5/6 Guillermo Polito <guillermopolito at gmail.com>:
>> >>>
>> >>>
>> >>> On Sun, May 6, 2012 at 2:16 PM, Esteban Lorenzano <estebanlm at gmail.com>
>> >>> wrote:
>> >>>>
>> >>>> <snip>
>> >>>> I'm more worried about having all-platforms-specific-stuff inside image...
>> >>>> but we can mitigate that with fuel, and making loadable packages when
>> >>>> running the image... I don't know, I'm just thinking while writing, so, this
>> >>>> is probably stupid :)
>> >>>>
>> >>>
>> >>> Just think how many times you took a development image and used it in
>> >>> several platforms.  At least I don't.  Same happened when I used Eclipse.  I
>> >>> didn't share my eclipses between systems.  Even, I had several eclipse
>> >>> installations with their own plugins (just like images, hehe).
>> >>>
>> >>> Probably with jenkins, metacello, and kernel/bootstrap we can generate
>> >>> distributions per platform (With the possibility of an all-in-one
>> >>> distribution for the ones who like that).
>> >>>
>> >>> Guille
>> >>
>> >> Yes, I understand that we can live without this feature...
>> >> - If we can reconstruct images easily (one of the goal of Pharo) - I
>> >> mean not only code, but any object (eventually with Fuel)
>> >> - If we solve the bootstrap problem (or if we can still prepare an
>> >> image for cross platform startup)
>> >> - If we don't forget to always talk (send messages) thru an abstract
>> >> layer, and never directly name the target library,
>> >>
>> >> Since I didn't have all these tools in the past, I were forced to use
>> >> development images across different platform a lot, and yes, it was
>> >> not following the mainstream rules (a la "we can reconstruct all from
>> >> scratch") but damn powerful.
>> >> For deploying applications, it also is very powerful and cheap.
>> >> Personally, I would feel sore to lose it.
>> >>
>> >
>> > But look at the root of what we are talking about: N bytes in VM
>> > versus M bytes in image to support certain functionality.
>> > I think if you need it, you will make sure that those bytes is there
>> > and properly packaged with you application.
>> >
>> Unfortunately, it's more than moving code...
>> What I mean is that when I need to pass an O_NONBLOCK flag to a FFI
>> call, it's going to be a problem because I have to know how this
>> information is encoded on each and every platform I want to support.
> But there are solutions to this which mean you *don't* have to know.  I wrote a prototype for VisualWorks that maps a SharedPool to these externally defined variables.  Here's how it works.
> For each group of C constants, e.g. i/o constants, one populates a subclasss of SharedPoolForC with the variables one wants to define, and in a class-side method one defines the set of include files per platform that one should pull in to evaluate the constants.  SharedPoolForC has code in it to automatically generate a C program, and compile it, e.g. to provide a shared library/dll for the current platform.  The C program is essentially a name-value dictionary that maps from the abstract name #O_NONBLOCK to the size and value for a particular platform.  SharedPoolForC also contains code to load the shared library/dll, extract the values and update the pool variables automatically.
> The deployment scheme is as follows, at start-up the system asks each SharedPoolForC subclass to check the platform and see if the platform has changed.  If it hasn't changed, nothing needs to happen.  If it has changed the system attempts to locate the shared library/dll for the current platform (the platform name is embedded in the dll's name), and update the pool variables from that dll, raising an exception if unavailable (and the exception could be mapped into a warning or an error to suit).  So to deploy e.g. a one-click one needs to generate the set of dlls fort the platforms one wants to deploy on.
> The development scheme is simply to run a method on the SharedPoolForC when one adds some class variables and/or changes the set of include files which turns the crank, generating, compiling and loading the C file to get the value(s) for the new variable(s).

Yes, i remember you told about it some years ago ;)

But this requires a platform with compiler installed. otherwise your
system won't be able to adopt to new environment. But of course there
is a solution to that as well: keep a database for every platform in
and detect platform on startup, hoping that everything is in sync :)
And if not, then it usually means that guy using either non-standard
distribution, or custom built kernel etc.. At this point i would stop
worrying about it, since if he is good enough to be able to customize
own system, he can deal with FFI troubles in no time..
and usually those guys having compiler installed :)

Also,  if system supports binary distributions, then we're in same boat
as any other binary compiled and distributed for that platform.. (need
to elaborate that?)

> An alternative scheme would generate a program that would print e.g. STON, which could be parsed or evaluated to compute the values.  This would have the advantage that the definitions of the values are readable and editable by mere humans.  So I think I'd discard the shared library/dll approach and keep it simple.
Indeed. Again, generate C code.. a bit more code doesn't hurts.

Best regards,
Igor Stasenko.

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