Native Extensions Fallback to Pure Ruby If Not Supported on Gem Install

Native extensions fallback to pure Ruby if not supported on gem install

This is my best result attempting to answer my own question to date. It appears to work for JRuby (tested in Travis and on my local installation under RVM), which was my main goal. However, I would be very interested in confirmations of it working in other environments, and for any input on how to make it more generic and/or robust:

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The gem installation code expects a Makefile as output from extconf.rb, but has no opinion on what that should contain. Therefore extconf.rb can decide to create a do nothing Makefile, instead of calling create_makefile from mkmf. In practice that might look like this:

ext/foo/extconf.rb

can_compile_extensions = false
want_extensions = true

begin
  require 'mkmf'
  can_compile_extensions = true
rescue Exception
  # This will appear only in verbose mode.
  $stderr.puts "Could not require 'mkmf'. Not fatal, the extensions are optional."
end

if can_compile_extensions && want_extensions
  create_makefile( 'foo/foo' )

else
  # Create a dummy Makefile, to satisfy Gem::Installer#install
  mfile = open("Makefile", "wb")
  mfile.puts '.PHONY: install'
  mfile.puts 'install:'
  mfile.puts "\t" + '@echo "Extensions not installed, falling back to pure Ruby version."'
  mfile.close

end

As suggested in the question, this answer also requires the following logic to load the Ruby fallback code in the main library:

lib/foo.rb (excerpt)

begin
  # Extension target, might not exist on some installations
  require 'foo/foo'
rescue LoadError
  # Pure Ruby fallback, should cover all methods that are otherwise in extension
  require 'foo/foo_pure_ruby'
end

Following this route also requires some juggling of rake tasks, so that the default rake task doesn't attempt to compile on Rubies that we're testing on that don't have capability to compile extensions:

Rakefile (excerpts)

def can_compile_extensions
  return false if RUBY_DESCRIPTION =~ /jruby/
  return true
end 

if can_compile_extensions
  task :default => [:compile, :test]
else
  task :default => [:test]
end

Note the Rakefile part doesn't have to be completely generic, it just has to cover known environments we want to locally build and test the gem on (e.g. all the Travis targets).

I have noticed one annoyance. That is by default you will see Ruby Gems' message Building native extensions. This could take a while..., and no indication that the extension compilation was skipped. However, if you invoke the installer with gem install foo --verbose you do see the messages added to extconf.rb, so it's not too bad.

Native C Extension if Library is Available

The have_library method has a return value:

Returns whether or not the given entry point func can be found within lib.

So you should be able to do this:

$defs.push('-DUSE_RUBY_UUID') if !have_library('uuid')
create_makefile("identifier")

And then set up your C to use libuuid if USE_RUBY_UUID is not defined and call into the Ruby UUID library if it is defined.

Oddly enough, the have_header and have_func methods in mkmf.rb add macros for you:

# File mkmf.rb, line 840
def have_header(header, preheaders = nil, &b)
  checking_for header do
    if try_header(cpp_include(preheaders)+cpp_include(header), &b)
      $defs.push(format("-DHAVE_%s", header.tr_cpp))
      true
    else
      false
    end
  end
end

but have_library makes you do it yourself.

Making a Ruby project that is not a gem (or some other kind)

You have to actually try to build a gem so this is easy!

to use bundler without Rails, a gem, whatever just create a directory

  mkdir my-non-gem-project
  cd my-non-gem-project

install bundler

  gem install bundler

and initialize your Gemfile

  bundle init

that will create a Gemfile for you and you can add to it and run bundle to install the dependencies from it

The simplest way to use bundler in your project would then be to open your main app file and add

require 'bundler/setup'
Bundler.require

This will require all of the gems you have in your Gemfile in the file this is added to. I am pretty sure that this file must be in the same directory as your Gemfile. More information here

Have fun with your Ruby project!

In depth Ruby Gem development resources (book, video, sites)

Rubygems aren't related to distributed programming.

Can you please provide more details about what you're after, if you aren't asking a duplicate question? Related questions within Stack Overflow include:

• Gotchas for writing rubygems
• Ruby : How to write a gem ?
• What are the steps needed to create and publish a rubygem of your own?
• What is the modern way to structure a ruby gem?

(I know this is more of a comment than an answer, but it's too big to fit in the comments section)

which gems for asynhronous HTTP-request processing exists?

There is a good talk about it here (look down for the slides):

http://lanyrd.com/2012/rubyconf/szpth/

The person giving the talk also has a comparison of all the ruby http clients, which indicates their concurrency model:

http://bit.ly/RubyHTTPClients

Best ruby binding/gem for curl/libcurl

I highly recommend Typhoeus. It relies on lib-curl, and allows for all sorts of parallel and async possibilities. It offers ssl, stubbing, follows redirects, allows custom headers, true parallel requests for blazing speed, and generally has yet to let me down. Also, it is well maintained--at the moment, the last commit was 2 days ago!

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