Load needed (dynamic) dependencies for provisioners at creation time.

The need for this change was initated with #293 which runs every
instance action in a thread of execution, even in serial mode. The issue
is that on the Mac platform MRI Ruby 1.9 and 2.0 (not confirmed for
2.1), dynamic (i.e. native) code needs to be loaded in the main thread
otherwise causing a "Trace/BPT trap: 5" crash.

References:

* http://stackoverflow.com/questions/9933969/matlab-ruby-gem-doesnt-work-when-called-from-thread#answer-12319780
* https://bugs.launchpad.net/sbcl/+bug/1014409

For Berkshelf 2.0.x at least, there are multiple transitive dependencies
that *could* load native code, meaning that `require 'berkshelf'` could
very well lead to a VM crash if performed in a thread other than main.

This commit pushes library loading code ahead to Provisioner creation
time. In other words, by the time you have a Provisioner object
reference either Berkshelf, Librarian-Chef, or nothing has been required
(assuming a Chef provisioner).

A drawback to this approach is that these dynamic dependencies will be
eagerly loaded when Test Kitchen is booting for trivial CLI commands
such as `kitchen list` and `kitchen diagnose`. Further work is needed to
ensure that `kitchen diagnose` remains viable even in the face of a
failure to load these dependencies.

Finally, the loaded version of Berkshelf or Librarian-Chef will be
displayed to the user on INFO for converge action and DEBUG on code
loading for troubleshooting.

Closes #357

/cc @reset, @ivey, @sethvargo

lib/kitchen/provisioner/base.rb

@@ -41,6 +41,7 @@ def initialize(config = {})
       def instance=(instance)
         @instance = instance
         expand_paths!
+        load_needed_dependencies!
       end
 
       # Returns the name of this driver, suitable for display in a CLI.
@@ -128,6 +129,8 @@ def expand_paths!
         end
       end
 
+      def load_needed_dependencies! ; end
+
       def logger
         instance ? instance.logger : Kitchen.logger
       end

lib/kitchen/provisioner/chef/berkshelf.rb

@@ -39,12 +39,15 @@ def initialize(berksfile, path, logger = Kitchen.logger)
           @logger     = logger
         end
 
+        def self.load!(logger = Kitchen.logger)
+          load_berkshelf!(logger)
+        end
+
         def resolve
-          info("Resolving cookbook dependencies with Berkshelf...")
+          version = ::Berkshelf::VERSION
+          info("Resolving cookbook dependencies with Berkshelf #{version}...")
           debug("Using Berksfile from #{berksfile}")
 
-          load_berkshelf!
-
           ::Berkshelf.ui.mute do
             if ::Berkshelf::Berksfile.method_defined?(:vendor)
               # Berkshelf 3.0 requires the directory to not exist
@@ -60,10 +63,17 @@ def resolve
 
         attr_reader :berksfile, :path, :logger
 
-        def load_berkshelf!
-          require 'berkshelf'
+        def self.load_berkshelf!(logger)
+          first_load = require 'berkshelf'
+
+          version = ::Berkshelf::VERSION
+          if first_load
+            logger.debug("Berkshelf #{version} library loaded")
+          else
+            logger.debug("Berkshelf #{version} previously loaded")
+          end
         rescue LoadError => e
-          fatal("The `berkshelf' gem is missing and must be installed" +
+          logger.fatal("The `berkshelf' gem is missing and must be installed" +
             " or cannot be properly activated. Run" +
             " `gem install berkshelf` or add the following to your" +
             " Gemfile if you are using Bundler: `gem 'berkshelf'`.")

lib/kitchen/provisioner/chef/librarian.rb

@@ -33,18 +33,22 @@ class Librarian
 
         include Logging
 
+
         def initialize(cheffile, path, logger = Kitchen.logger)
           @cheffile   = cheffile
           @path       = path
           @logger     = logger
         end
 
+        def self.load!(logger = Kitchen.logger)
+          load_librarian!(logger)
+        end
+
         def resolve
-          info("Resolving cookbook dependencies with Librarian-Chef")
+          version = ::Librarian::Chef::VERSION
+          info("Resolving cookbook dependencies with Librarian-Chef #{version}...")
           debug("Using Cheffile from #{cheffile}")
 
-          load_librarian!
-
           env = ::Librarian::Chef::Environment.new(
             :project_path => File.dirname(cheffile))
           env.config_db.local["path"] = path
@@ -54,12 +58,19 @@ def resolve
 
         attr_reader :cheffile, :path, :logger
 
-        def load_librarian!
-          require 'librarian/chef/environment'
+        def self.load_librarian!(logger)
+          first_load = require 'librarian/chef/environment'
           require 'librarian/action/resolve'
           require 'librarian/action/install'
+
+          version = ::Librarian::Chef::VERSION
+          if first_load
+            logger.debug("Librarian-Chef #{version} library loaded")
+          else
+            logger.debug("Librarian-Chef #{version} previously loaded")
+          end
         rescue LoadError => e
-          fatal("The `librarian-chef' gem is missing and must be installed" +
+          logger.fatal("The `librarian-chef' gem is missing and must be installed" +
             " or cannot be properly activated. Run" +
             " `gem install librarian-chef` or add the following to your" +
             " Gemfile if you are using Bundler: `gem 'librarian-chef'`.")

lib/kitchen/provisioner/chef_base.rb

@@ -129,6 +129,16 @@ def create_sandbox
 
       protected
 
+      def load_needed_dependencies!
+        if File.exists?(berksfile)
+          debug("Berksfile found at #{berksfile}, loading Berkshelf")
+          Chef::Berkshelf.load!(logger)
+        elsif File.exists?(cheffile)
+          debug("Cheffile found at #{cheffile}, loading Librarian-Chef")
+          Chef::Librarian.load!(logger)
+        end
+      end
+
       def format_config_file(data)
         data.each.map { |attr, value|
           [attr, (value.is_a?(Array) ? value.to_s : %{"#{value}"})].join(" ")