It seems there's no uint32_t or uint64_t for JRuby/FFI on OS X:

Environment

jruby 9.1.2.0 (2.3.0) 2016-05-26 7357c8f Java HotSpot(TM) 64-Bit Server VM 25.45-b02 on 1.8.0_45-b14 +jit [darwin-x86_64]

Darwin Daniels-MacBook-Pro.local 15.5.0 Darwin Kernel Version 15.5.0: Tue Apr 19 18:36:36 PDT 2016; root:xnu-3248.50.21~8/RELEASE_X86_64 x86_64

ffi (1.9.10 java)

When running against some dev sys-proctable code I get this warning and error:

jruby: warning: unknown property jruby.cext.enabled
TypeError: unable to resolve type 'uint32_t'