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comp.lang.ruby

[ANN] FFI 0.1.1 (Foreign Function Interface) for Ruby 1.8.6/7 and 1.9

Charles Oliver Nutter

10/31/2008 11:17:00 PM

The JRuby team is proud to announce the release of FFI for Ruby 1.8.6/7
and 1.9!

FFI (gem install ffi) is a library for programmatically loading dynamic
libraries, binding functions within them, and calling those functions
from Ruby code. Here's a quick sample of binding and calling the getpid
C library function:


require 'ffi'

module GetPid
extend FFI::Library

attach_function :getpid, [], :uint
end

puts GetPid.getpid


Here's another, calling qsort and passing a Ruby block as a C callback:


require 'ffi'

module LibC
extend FFI::Library
callback :qsort_cmp, [ :pointer, :pointer ], :int
attach_function :qsort, [ :pointer, :int, :int, :qsort_cmp ], :int
end

p = MemoryPointer.new(:int, 2)
p.put_array_of_int32(0, [ 2, 1 ])
puts "Before qsort #{p.get_array_of_int32(0, 2).join(', ')}"
LibC.qsort(p, 2, 4) do |p1, p2|
i1 = p1.get_int32(0)
i2 = p2.get_int32(0)
i1 < i2 ? -1 : i1 > i2 ? 1 : 0
end
puts "After qsort #{p.get_array_of_int32(0, 2).join(', ')}"


I posted a blog entry with a longer description of the library,
additional examples, and links to some other documentation and posts.
Docs are a little slim at this point, so feel free to experiment and
update the JRuby wiki page:

http://wiki.jruby.org/wiki/Calling_C_...

I'm sure docs from here will filter back into the library and out into
the general cosmos.

Finally, there's no need to write a C extension to call C libraries, and
the same FFI code will work in Ruby 1.8.6/7, Ruby 1.9, JRuby 1.1.4+, and
Rubinius (though Rubinius has no callback support yet).

Don't be an extension stooge! Use FFI!

- Charlie
60 Answers

Thomas Hurst

11/1/2008 1:39:00 AM

0

* Charles Oliver Nutter (charles.nutter@sun.com) wrote:

> The JRuby team is proud to announce the release of FFI for Ruby
> 1.8.6/7 and 1.9!

> Finally, there's no need to write a C extension to call C libraries,
> and the same FFI code will work in Ruby 1.8.6/7, Ruby 1.9, JRuby
> 1.1.4+, and Rubinius (though Rubinius has no callback support yet).

Awesome. I've used DL to link up some custom libs to a Ruby service,
will give FFI a go and see how it compares :)

Are things like structs likely to be supported in future, ala Python
ctypes?

--
Thomas 'Freaky' Hurst
http...

Charles Oliver Nutter

11/1/2008 5:41:00 AM

0

Thomas Hurst wrote:
> * Charles Oliver Nutter (charles.nutter@sun.com) wrote:
>
>> The JRuby team is proud to announce the release of FFI for Ruby
>> 1.8.6/7 and 1.9!
>
>> Finally, there's no need to write a C extension to call C libraries,
>> and the same FFI code will work in Ruby 1.8.6/7, Ruby 1.9, JRuby
>> 1.1.4+, and Rubinius (though Rubinius has no callback support yet).
>
> Awesome. I've used DL to link up some custom libs to a Ruby service,
> will give FFI a go and see how it compares :)
>
> Are things like structs likely to be supported in future, ala Python
> ctypes?

Actually structs are already supported! See the blog post, and I believe
there's some examples shipped with the gem. There needs to be more docs,
certainly, and hopefully they'll get some TLC soon.

Also, I forgot to call out Evan Phoenix for coming up with the API and
initial design, and he or someone else on Rubinus wrote up the
templating/header-file-processing stuff as well. And of course a huge
thanks to Wayne Meissner for implementing FFI not just once (for JRuby)
but twice (for C Ruby). His work will mean a huge leap forward in
cross-impl portability.

- Charlie

Radoslaw Bulat

11/1/2008 8:39:00 AM

0

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Charles Oliver Nutter

11/1/2008 10:18:00 AM

0

RadosÅ?aw BuÅ?at wrote:
> On Sat, Nov 1, 2008 at 6:40 AM, Charles Oliver Nutter
> <charles.nutter@sun.com> wrote:
>> Actually structs are already supported! See the blog post, and I believe
>> there's some examples shipped with the gem.
>
> Your blog is preaty known but for clarity:
> http://blog.headius.com/2008/10/ffi-for-ruby-now-avai...
> :-)

Oh right, a link would have been useful. Thank you :)

- Charlie

Charles Oliver Nutter

11/1/2008 10:19:00 AM

0

Charles Oliver Nutter wrote:
> I posted a blog entry with a longer description of the library,
> additional examples, and links to some other documentation and posts.

And then I completely forgot to include the blog post URL...

http://blog.headius.com/2008/10/ffi-for-ruby-now-avai...

- Charlie

Luc Heinrich

11/1/2008 10:26:00 AM

0

On 1 nov. 08, at 11:19, Charles Oliver Nutter wrote:

> And then I completely forgot to include the blog post URL...

Looks cool, great work.

Two questions:

- Are variadic functions supported?
- Do you have any idea or measurements of the overhead of calling
through FFI as opposed to using a compiled extension?

--
Luc Heinrich - luc@honk-honk.com

Charles Oliver Nutter

11/1/2008 11:16:00 AM

0

Luc Heinrich wrote:
> On 1 nov. 08, at 11:19, Charles Oliver Nutter wrote:
>
>> And then I completely forgot to include the blog post URL...
>
> Looks cool, great work.
>
> Two questions:
>
> - Are variadic functions supported?
> - Do you have any idea or measurements of the overhead of calling
> through FFI as opposed to using a compiled extension?

Wayne answers the latter, sorta, on his followup blog post:

http://blog.headius.com/2008/10/ffi-for-ruby-now-avai...

He doesn't have specific numbers for performance at the moment, but the
short story is that FFI introduces a bit of overhead; ultimately I
believe that the overhead gets lost in the flow of a Ruby application,
especially when you're tossing units of work across like SQL queries or
arrays. Wayne probably can fill in more details on what the actual
overhead is like.

And I'd also expect that any small amount of overhead is vastly
outweighed by the ability to write an FFI-based library once and use it
across implementations.

- Charlie

Luc Heinrich

11/1/2008 9:25:00 PM

0

On 1 nov. 08, at 12:16, Charles Oliver Nutter wrote:

> He doesn't have specific numbers for performance at the moment, but
> the short story is that FFI introduces a bit of overhead; ultimately
> I believe that the overhead gets lost in the flow of a Ruby
> application, especially when you're tossing units of work across
> like SQL queries or arrays.

# --- [begin unscientific test] --------

require 'rubygems'
require 'benchmark'
require 'zlib'
require 'ffi'
require 'dl/import'

module Zlib_ffi
extend FFI::Library
attach_function :zlib_version, :zlibVersion, [], :string
end

module Zlib_dl
extend DL::Importable
dlload "libz.dylib"
extern "const char* zlibVersion()"
end

puts Zlib.zlib_version
puts Zlib_ffi.zlib_version
puts Zlib_dl.zlibVersion

Benchmark.bm(3) do |bm|
bm.report("ext") { 500_000.times { Zlib.zlib_version } }
bm.report("ffi") { 500_000.times { Zlib_ffi.zlib_version } }
bm.report("dl") { 500_000.times { Zlib_dl.zlibVersion } }
end

# --- [end unscientific test] --------

This gives the following results:

1.2.3
1.2.3
1.2.3
user system total real
ext 1.050000 0.320000 1.370000 ( 1.373800)
ffi 2.160000 0.660000 2.820000 ( 2.818966)
dl 3.500000 1.060000 4.560000 ( 4.552789)

All this using MacPorts MRI 1.8.7-p72 under OS X 10.5.5. The observed
overhead is slightly over 2x for ffi, probably not a big deal unless
ffi calls are used in tight loops I guess.


PS: haven't seen any trace of variadic function support in the code.

--
Luc Heinrich - luc@honk-honk.com

Radoslaw Bulat

11/1/2008 11:20:00 PM

0

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Radoslaw Bulat

11/1/2008 11:23:00 PM

0

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