Ruby FFI

Ruby FFIThe Foreign Function Interface for accessing system wide shared libraries in Ruby Angel Pizarro angel@upenn.edu

Ruby C Extension API• Ruby has a C extension mechanism • Use SWIG to wrap a C API • Non-idiomatic Ruby :( • Also IO struct changed between 1.8 and 1.9, SWIG needs new typemap • Write your own C modules using this API • Other Ruby VM’s out in the cold

Ruby FFI• Foreign Function Interface, based on libfﬁA foreign function interface [...] allows code written inone language to call code written in another language.The libffi library really only provides the lowest,machine dependent layer of a fully featured foreignfunction interface. A layer must exist above libffi thathandles type conversions for values passed between thetwo languages.• MRI, MacRuby, Rubinius and JRuby support

Given a C API : libcairo

Mapping Functions

Function Input Args

Function Input ArgsThat sucks! We lose all method signature information!

Types, Enums & Constants

Types, Enums & Constants still sucks

Types, Enums & Constants still sucks Alias a type: Method sig now becomes nicer:

Structs

Managed Structs DANGER WILL ROBINSON!Only use if you REALLY want Ruby GC to manage references and memory

Final Notes• Beware library calls that open STIN / STDOUT to buffer writes • Speciﬁcally, they may close the socket and Ruby IO becomes FUBAR• Multi-dimensional arrays in structs not supported (“unroll” the previous dimension)• Do not use ManagedStruct if you just want type casting on a pointer ref• Essentially still using C idioms to code (e.g. memory management)

Ruby FFI

by delagoya on Feb 09, 2011

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Ruby FFI — Presentation Transcript