Developing Ruby gems with native extensions

Presented at Geneva.rb on 21st January 2015

Transcript

1. Developing Ruby gems
   with native extensions
   by @crackofdusk
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2. Why use native
   extensions?
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3. Bindings to existing native libraries
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4. Speed up hot code paths
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5. Why not use native
   extensions
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6. The current speed is acceptable
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7. The speed can be improved by an
   algorithmic change
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8. You are uncomfortable with C and there is a
   another communication channel with the
   underlying system
   (HTTP, UNIX sockets, ...)
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9. Let’s dive in
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10. $ tree
    .
    ├── ext
    │ └── hello
    │ ├── extconf.rb
    │ └── hello.c
    └── hello.gemspec
    ext/hello/extconf.rb
    require 'mkmf'
    have_library('hello')
    create_makefile('hello/hello')
    ext/hello/hello.c
    #include
    void Init_hello() {
    // ...
    }
    hello.gemspec
    Gem::Specification.new do |spec|
    # ...
    spec.extensions <<
    'ext/hello/extconf.rb'
    end
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11. $ cd ext/hello
    $ ruby extconf.rb
    checking for main() in -lhello... no
    creating Makefile
    $ make
    compiling hello.c
    linking shared-object hello/hello.so
    $ irb
    irb(main):001:0> require './hello'
    => true
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12. $ tree
    .
    ├── ext
    │ └── hello
    │ ├── extconf.rb
    │ └── hello.c
    ├── lib
    └── Rakefile
    $ rake compile
    ...
    $ ls lib/
    hello.so
    $ irb -Ilib
    irb(main):001:0> require 'hello'
    => true
    Rakefile
    require 'rake/extensiontask'
    Rake::ExtensionTask.new('hello')
    With the rake-compiler gem
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13. extconf.rb
    Checks compilation conditions and generates a Makefile. For example:
    require 'mkmf'
    HEADER_DIRS = [
    # ...
    ]
    LIB_DIRS = [
    # ...
    ]
    unless find_header('foo/foo.h', *HEADER_DIRS)
    abort "libfoo is missing. Please install libfoo"
    end
    unless find_library('foo', 'foo_imported_function', *LIB_DIRS)
    abort "libfoo is missing. Please install libfoo"
    end
    create_makefile('foo/foo')
    See the MakeMakefile documentation for all available checks.
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14. Library initialization and entry point
    When the interpreter loads the library LIBRARY, it executes the Init_LIBRARY()
    function.
    #include
    #include
    void Init_foo(void) {
    VALUE mFoo = rb_define_module("Foo");
    rb_define_singleton_method(mFoo, "bar", bar, 1);
    //...
    }
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15. Ruby Extension API
    Used by the library to interact with the Ruby interpreter from the C code.
    It provides functions to:
    check data types
    convert between different types
    define classes, modules, constants, methods
    invoke Ruby methods
    raise exceptions
    handle allocations and deallocations
    wrap C pointers into Ruby objects
    etc.
    The documentation is in the README.EXT file that comes with the CRuby source
    code.
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16. Further reading
    Official documentation about making extension libraries for Ruby:
    https://github.com/ruby/ruby/blob/trunk/README.EXT
    Rubygems guide about gems with extensions:
    http://guides.rubygems.org/gems-with-extensions/
    The rake-compiler gem:
    https://github.com/rake-compiler/rake-compiler
    Writing Ruby C extensions:
    http://tenderlovemaking.com/2009/12/18/writing-ruby-c-extensions-part-
    1.html
    http://tenderlovemaking.com/2010/12/11/writing-ruby-c-extensions-part-
    2.html
    Native extensions with Java:
    https://blog.jcoglan.com/2012/08/02/your-first-ruby-native-extension-java/
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