Structuring complexly-interdependent C/Ruby libraries

Eric_Peden · 28 February 2005 07:34

First post. Hi.

I'm writing a ray-tracer in Ruby (I know, I know...) Perhaps some other time I'll wax ecstatic over the advantages Ruby brings to such a project, but at the moment I have less pleasant issues I'm hoping to get some help with.

A pure-Ruby ray tracer is just a tad slow. Clearly, some core functionality needs to be implemented in C for speed. The system is broken into classes similar to the following:

   Camera
   Engine
   Vector
   Point
   Ray
   Shape
     Sphere
     Polygon

Of those classes, only a handful are performance critical, and of each of those, only one or two methods are true bottlenecks. I'm trying to keep as much of the code as possible in Ruby, while breaking out only the real work horses into C. Vector, for example, is almost pure C, whereas only the intersection-testing method in the Shape subclasses is in C. Unfortunately, I keep running into dependency problems when trying to build the C functions. My C code is organized like this:

   ext/
    extconf.rb
    ext.c
    vector.c
    sphere.c

When built, this generates a single library that includes the code for all of the optimized classes. 'ext.c' has an Init_ function that calls initialization routines in the other files. Here's an example from sphere.c:

   Init_Sphere() {
       VALUE cSphere = rb_const_get(rb_cObject, rb_intern("Sphere"));
   }

sphere.rb would look something like this:

require 'vector'
require 'ext/optimized'

   class Sphere < Shape
     ...
   end

When I run this, I get a "undefined constant" error from the C code, which makes sense: when the C library is included, Sphere hasn't been defined yet. So I just move the "require 'ext/optimized'" to the bottom of sphere.rb, right? Sadly, no. There's only one library entry point, so I have to initialize all of my optimized classes at the same time. 'vector.rb' also requires 'ext/optimized', so Init_Sphere() would still get called before Sphere is actually defined, and I'll still get my error. Furthermore, since Vector gets used in several other files, I have to worry about the order in which those files are parsed, as well.

I can see a few solutions: one is to break out every C file so that it compiles into its own library. This would leave me with an ugly file structure, since I'd need either a new extconf.rb for each C file, or a sub-directory for each source file. I've tried doing something like this:

VALUE cSphere = rb_eval_string("class Shape; end; class Sphere < Shape; end");

but that feels extremely naughty, not to mention requires me to duplicate the heritage of each subclass I want to provide C extensions for. I suppose I could also create a "Optimizer" object in my C library's Init() method, and attach methods to that class that would call the class-specific Init_...() methods:

   # a .rb file
   require 'ext/optimized'
   class Sphere < Shape
     ..
   end
   Optimizer.init_sphere

But that also seems rather distasteful.

I apologize for my wordiness... I'm trying to make my situation clear. Am I making this more difficult than it really is? If the classes involved where pure-C, or if there wasn't any subclassing, I'd be fine. I just can't see how to manage the class dependencies while dealing with a single library entry point, and so I've come to seek the guidance of the wizards. Any help--or even architecture bashing, if it's constructive--is appreciated.

···

--
eric

Pit · 28 February 2005 10:23

Eric Peden schrieb:

First post. Hi.

Welcome!

(...code snipped...)

When I run this, I get a "undefined constant" error from the C code, which makes sense: when the C library is included, Sphere hasn't been defined yet.

I've never extended Ruby with C yet, but couldn't you create the optimized classes in C and later add some Ruby methods to them?

Regards,
Pit

leon_breedt1 · 28 February 2005 10:58

I always define classes with C elements in the extension itself.

You know you can define a class and the methods on it in Ruby as many
times as you want as long as you don't change the inheritance? So its
no problem to later in Ruby redefine the class with its pure-Ruby
methods.

Leon

···

On Mon, 28 Feb 2005 16:34:21 +0900, Eric Peden <eric@ericpeden.com> wrote:

I apologize for my wordiness... I'm trying to make my situation clear.
Am I making this more difficult than it really is? If the classes
involved where pure-C, or if there wasn't any subclassing, I'd be fine.
I just can't see how to manage the class dependencies while dealing
with a single library entry point, and so I've come to seek the
guidance of the wizards. Any help--or even architecture bashing, if
it's constructive--is appreciated.

George5 · 28 February 2005 11:05

Eric Peden wrote:

First post. Hi.

I'm writing a ray-tracer in Ruby (I know, I know...) Perhaps some other time I'll wax ecstatic over the advantages Ruby brings to such a project, but at the moment I have less pleasant issues I'm hoping to get some help with.

A pure-Ruby ray tracer is just a tad slow. Clearly, some core functionality needs to be implemented in C for speed. The system is broken into classes similar to the following:

  Camera
  Engine
  Vector
  Point
  Ray
  Shape
    Sphere
    Polygon

Of those classes, only a handful are performance critical, and of each of those, only one or two methods are true bottlenecks. I'm trying to keep as much of the code as possible in Ruby, while breaking out only the real work horses into C. Vector, for example, is almost pure C, whereas only the intersection-testing method in the Shape subclasses is in C. Unfortunately, I keep running into dependency problems when trying to build the C functions. My C code is organized like this:

  ext/
   extconf.rb
   ext.c
   vector.c
   sphere.c

You might take a look at RubyInline:

http://rubyforge.org/projects/rubyinline/

It will allow you to put the C code right into your Ruby classes.

Regards,

Michael

Kaspar_Schiess · 28 February 2005 11:12

Hello Eric,

Usually, you define classes in your C extension and likewise in your Ruby
code, doing things twice, which does not matter since Ruby will take your
meaning (creating one class).

-- myclass.c
Init_... {
cMyClass = rb_define_class_under( mMyModule, "MyClass", rb_cObject );
}

-- myclass.rb
require 'myclass.so'
class MyClass
# ...
end

But yeah, redefinition with a different superclass gives you a
SuperClassMismatch. So I would aim for different classes altogether, using
mixins to mix the c code into the Ruby code:

-- myclass.c
Init_... {
mMyClassMixin = rb_define_module_under( mMyModule, "MyClassCMixin" );
...
}

-- myclass.rb
require 'myclasscmixin'

class MyClass < MySuperClass
include MyClassCMixin
#...
end

This method is tested and works, and it looks clean enough to me. Now does
this solve all your problems ? Yes, if I read you right.

k

code manufacture & ruby lab at http://www.tua.ch/ruby

···

--
The man who sets out to carry a cat by its tail learns something that will
always be useful and which never will grow dim or doubtful.
-- Mark Twain

Eric_Peden · 28 February 2005 15:44

I have looked at RubyInline (and in fact use it in a couple of places in my code). It works great for shorter methods. However, for longer methods, or classes where I C-ify several methods, I prefer breaking the code out in a .c file. This makes my text editor happy, and lets me work with C-specific syntax highlighting and autocompletion features.

There are also a few times where I want to work directly with the C representation of another optimized class, and I had trouble doing this with Inline. This was early on in my explorations, so it's likely I was just doing things the wrong way.

Thanks for the suggestion!

···

On Feb 28, 2005, at 5:05 AM, Michael Neumann wrote:

You might take a look at RubyInline:

http://rubyforge.org/projects/rubyinline/

It will allow you to put the C code right into your Ruby classes.

--
eric

Eric_Peden · 28 February 2005 15:50

Usually, you define classes in your C extension and likewise in your Ruby
code, doing things twice, which does not matter since Ruby will take your
meaning (creating one class).

This was suggested by several people (thanks, Pit and Leon!), and not only captures the essence of Ruby, but would work quite well... if it weren't for my need for inheritance, as you point out shortly. I _could_ also create "empty" versions of my superclasses in C, but then I'm recreating the inheritance hierarchy again. Or...

But yeah, redefinition with a different superclass gives you a
SuperClassMismatch. So I would aim for different classes altogether, using
mixins to mix the c code into the Ruby code:

<snip>

This method is tested and works, and it looks clean enough to me. Now does
this solve all your problems ? Yes, if I read you right.

...I could just do this. I believe this is exactly what I need. Thanks for the help!

···

On Feb 28, 2005, at 5:12 AM, Kaspar Schiess wrote:

--
eric

Kaspar_Schiess · 28 February 2005 16:39

(In response to news:07967b482240386ccb35046cc1422ac0@ericpeden.com by Eric
Peden)

...I could just do this. I believe this is exactly what I need. Thanks
for the help!

np. Just found out about this too. Thanks for asking the cool question.

k

···

--
code manufacture & ruby lab at tua.ch - und andere Domains günstig und einfach online kaufen auf top-domains.ch
.o.
..o
ooo

leon_breedt1 · 1 March 2005 03:19

I'm not sure you need to recreate it:

class Super
end

class Test < Super
  def one
    puts "one!"
  end
end

t1 = Test.new

class Test
  def two
    puts "two!"
  end
end

t2 = Test.new

puts t1.class.ancestors.inspect
puts t2.class.ancestors.inspect

It appears that Ruby "remembers" the ancestry from the first time that
class was defined using that name.

So if you define it in C first, and in your Ruby code, require the
extension before redefining the classes, you don't need to recreate
the inheritance hierarchy.

Leon

···

On Tue, 1 Mar 2005 00:50:29 +0900, Eric Peden <eric@ericpeden.com> wrote:

This was suggested by several people (thanks, Pit and Leon!), and not
only captures the essence of Ruby, but would work quite well... if it
weren't for my need for inheritance, as you point out shortly. I
_could_ also create "empty" versions of my superclasses in C, but then
I'm recreating the inheritance hierarchy again. Or...

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