1. FFI
MAKING CROSS ENGINE EXTENSIONS
Jeremy Hinegardner
jeremy@copiousfreetime.org
twitter: copiousfreetime

2. COPIOUS FREE TIME
Fedora Ruby
Packaging Gems
•beanstalkd •keybox
•haproxy •rabal
•libtomcrypt •launchy
•libtommath •heel
•nginx •htauth
•ragel •amalgalite
•tinyproxy •hitimes
•stickler
•crate

3. I LOVE RUBY

4. I LIKE C

5. ANY
EXTENSION DEVELOPERS
IN THE HOUSE ?

6. WHO HAS USED FFI?

7. WHO HAS HEARD OF FFI?

8. WHAT IS FFI?

9. LIBFFI
http://sourceware.org/libffi/
“A foreign function interface is the
popular name for the interface that
allows code written in one language
to call code written in another
language.”

10. e
m
i
Application
t
n
uses
u
libsomething_foo()
R FFI
libsomething.so

11. App App
JRuby Rubinius
Interpreter Interpreter
App
Matz Ruby
something-ffi (pure ruby)
Interpreter
ruby-somethingor ffi gem
built-in libffi C extension
libsomething.so

12. 1 #ifndef __SIMPLE_METRICS_H__
2 #define __SIMPLE_METRICS_H__
3 #include <stdlib.h>
4 #include <math.h>
5
6 typedef struct _simple_metrics{
7 double min;
8 double max;
9 double sum;
10 double sumsq;
11 long count;
12 } simple_metrics ;
13
14 simple_metrics* simple_metrics_new();
15 void simple_metrics_free( simple_metrics* sm );
16 void simple_metrics_update( simple_metrics* sm, double value );
17 double simple_metrics_mean( simple_metrics* sm );
18 double simple_metrics_min( simple_metrics* sm );
19 double simple_metrics_max( simple_metrics* sm );
20 double simple_metrics_sum( simple_metrics* sm );
21 long simple_metrics_count( simple_metrics* sm );
22 double simple_metrics_stddev( simple_metrics* sm );
23 double simple_metrics_rate( simple_metrics* sm );
24
25 #endif

13. 1 class Metric
2 attr_reader :name
3 def initialize( name )
4 @name
5 end
6
7 def update( new_value) ... end
8 def count ... end
9 def max ... end
10 def mean ... end
11 def min ... end
12 def rate ... end
13 def sum ... end
14 def stddev ... end
15 end

14. 142 void Init_simple_metrics_ext()
143 {
144 VALUE cSM_Common;
145
146 mSM = rb_define_module( quot;SimpleMetricsquot; );
147 mSME = rb_define_module_under( mSM, quot;Extquot; );
148
149 /* load the class we inherit from */
150 rb_require(quot;simplemetrics/commonquot;);
151
152 cSM_Common = rb_const_get( mSM, rb_intern( quot;Commonquot; ) );
153
154 cSME_Metric = rb_define_class_under( mSME, quot;Metricquot;, cSM_Common );
155
156 rb_define_alloc_func(cSME_Metric, sm_alloc);
157 rb_define_method( cSME_Metric, quot;initializequot;, sm_initialize, 1 );
158 rb_define_method( cSME_Metric, quot;updatequot;, sm_update, 1 );
159 rb_define_method( cSME_Metric, quot;countquot;, sm_count, 0 );
160 rb_define_method( cSME_Metric, quot;maxquot;, sm_max, 0 );
161 rb_define_method( cSME_Metric, quot;minquot;, sm_min, 0 );
162 rb_define_method( cSME_Metric, quot;meanquot;, sm_mean, 0 );
163 rb_define_method( cSME_Metric, quot;ratequot;, sm_rate, 0 );
164 rb_define_method( cSME_Metric, quot;sumquot;, sm_sum, 0 );
165 rb_define_method( cSME_Metric, quot;stddevquot;, sm_stddev, 0 );
166
167 }

15. 7 module SimpleMetrics
8 module FFI
9
10 class Struct < ::FFI::ManagedStruct
11 layout :min, :double, :max, :double, :sum, :double,
12 :sumsq, :double, :count, :long
13 def self.release( ptr )
14 SimpleMetrics::FFI.simple_metrics_free( ptr )
15 end
library function parameters return type
16 end
17
18 extend ::FFI::Library
19 ffi_lib quot;libsimple_metricsquot;
20
21 attach_function :simple_metrics_new, [ ], :pointer
22 attach_function :simple_metrics_free, [ :pointer ], :void
23 attach_function :simple_metrics_update,[ :pointer, :double ], :void
24 attach_function :simple_metrics_min, [ :pointer ], :double
25 attach_function :simple_metrics_max, [ :pointer ], :double
26 attach_function :simple_metrics_mean, [ :pointer ], :double
27 attach_function :simple_metrics_sum, [ :pointer ], :double
28 attach_function :simple_metrics_count, [ :pointer ], :long
29 attach_function :simple_metrics_stddev,[ :pointer ], :double
30 attach_function :simple_metrics_rate, [ :pointer ], :double
31
32 end
33 end

16. 35 module SimpleMetrics
36 module FFI
37 class Metric < ::SimpleMetrics::Common
38 include ::SimpleMetrics::FFI
39 def initialize( name )
40 super
41 @impl = FFI.simple_metrics_new
42 end
43
44 def update( v )
45 simple_metrics_update( @impl, v )
46 end
47
48 self.keys.each do |f|
49 module_eval <<-code
50 def #{f}
51 simple_metrics_#{f}( @impl )
52 end
53 code
54 end
55 end
56 end
57 end

17. 10 class Struct < ::FFI::ManagedStruct 6 typedef struct _simple_metrics{
11 layout :min, :double, 7 double min;
12 :max, :double, 8 double max;
13 :sum, :double, 9 double sum;
14 :sumsq, :double, 10 double sumsq;
15 :count, :long 11 long count;
16 def self.release( ptr ) 12 } simple_metrics ;
17 SimpleMetrics::FFI.simple_metrics_free( ptr )
18 end
19 end

18. 21 extend ::FFI::Library
22 ffi_lib quot;libsimple_metricsquot;
23
24 attach_function :simple_metrics_new, [ ], :pointer
25 attach_function :simple_metrics_free, [ :pointer ], :void
26 attach_function :simple_metrics_update,[ :pointer, :double ], :void
27 attach_function :simple_metrics_mean, [ :pointer ], :double
28 attach_function :simple_metrics_min, [ :pointer ], :double
29 attach_function :simple_metrics_max, [ :pointer ], :double
30 attach_function :simple_metrics_sum, [ :pointer ], :double
31 attach_function :simple_metrics_count, [ :pointer ], :long
32 attach_function :simple_metrics_stddev,[ :pointer ], :double
33 attach_function :simple_metrics_rate, [ :pointer ], :double
14 simple_metrics* simple_metrics_new();
15 void simple_metrics_free( simple_metrics* sm );
16 void simple_metrics_update( simple_metrics* sm, double value );
17 double simple_metrics_mean( simple_metrics* sm );
18 double simple_metrics_min( simple_metrics* sm );
19 double simple_metrics_max( simple_metrics* sm );
20 double simple_metrics_sum( simple_metrics* sm );
21 long simple_metrics_count( simple_metrics* sm );
22 double simple_metrics_stddev( simple_metrics* sm );
23 double simple_metrics_rate( simple_metrics* sm );

19. MEANINGLESS METRICS
Traditional C
FFI
Extension
Jeremy’s Time 40 minutes 70 minutes
1 Million update()
1.16 sec 0.42 sec
calls
Will it Blend run
Yes No
on JRuby?

20. % ruby ~/Projects/simple_metrics/example/bench.rb 1000000
generating 1000000 random numbers between 0 and 10,000
Rehearsal -----------------------------------------------
ext 0.420000 0.000000 0.420000 ( 0.460806)
ffi 1.160000 0.000000 1.160000 ( 1.171498)
-------------------------------------- total: 1.580000sec
user system total real
ext 0.420000 0.010000 0.430000 ( 0.424809)
ffi 1.160000 0.000000 1.160000 ( 1.182928)
% ./bin/jruby ~/Projects/simple_metrics/example/bench.rb 1000000
generating 1000000 random numbers between 0 and 10,000
Skipping Ext
Rehearsal -----------------------------------------------
ffi 0.922000 0.000000 0.922000 ( 0.922000)
-------------------------------------- total: 0.922000sec
user system total real
ffi 0.834000 0.000000 0.834000 ( 0.834000)

21. FFI GEMS
ffi-ncurses tidy_ffi
4
ffi-swig-generator ffi-zlib

22. GEMS WITH EXTENSIONS
346
Out of 4,501 gems

23. GET
TO
WORK!!

24. THANKS
• Wayne Meissner - adding libffi to JRuby and providing the
ffi gem for MRI.
• Evan Phoenix - using libffi in Rubinius
• Authors of the examples on the Project Kenai wiki

25. LINKS
http://blog.headius.com/2008/10/ffi-for-ruby-now-available.html
•
http://kenai.com/projects/ruby-ffi
•
http://wmeissner.blogspot.com/
•
http://www.igvita.com/2009/01/15/bridging-mri-jruby-rubinius-with-ffi/
•
http://blog.segment7.net/articles/2008/01/15/rubinius-foreign-function-
•
interface

26. QUESTIONS?