My setup is OSX 10.6.7
ruby 1.9.2p180 (2011-02-18 revision 30909) [x86_64-darwin10.7.0]

Here is a collection of relevant code

ffi_lib '/System/Library/Frameworks/CoreMIDI.framework/Versions/
Current/CoreMIDI'

I am passing this callback

EventCallback = FFI::Function.new(:void,
[:pointer, :pointer, :pointer]) do | newPackets_ptr, refCon_ptr,
connRefCon_ptr |
      puts "hello from the callback"
end

to this method:

attach_function :MIDIInputPortCreate,
[:pointer, :pointer, :pointer, :pointer, :pointer], :int

MIDIInputPortCreate(@client, port_name, EventCallback, nil,
endpoint_ptr)

(which is returning 0 / no error)

The print statement is never called, nor do I receive any errors or
segfault.

I have tried passing :blocking => true to FFI::Function.new...using a
Proc instead, using instance variables instead of a constant. I've
tried changing the number of parameters on EventCallback to see if I
could force an exception but even that didn't result in anything.

I am able to successfully interact with other methods in the system
library--this callback is the only issue

Here is a reference for the method I am passing the callback to:
http://xmidi.com/docs/coremidi22.html

And for the callback:
http://xmidi.com/docs/coremidi77.html

I can send more code if needed. I am hoping someone who has worked
with ruby-ffi in OSX will see the issue right off the bat. I've worked
with ffi in windows and linux before but this is new to me.

Any ideas are of course appreciated. Thanks