First pass at pre-caching the cassettes.

lib/vcr/cassette/cache.rb

@@ -1,3 +1,5 @@
+require 'thread'
+
 module VCR
   class Cassette
     class Cache
@@ -7,22 +9,52 @@ def initialize
                              File.read(file_name) :
                              nil
         end
+
+        @mutex = Mutex.new
+        @file_queue = Queue.new
       end
 
       def [](file_name)
-        @files[file_name]
+        @mutex.synchronize do
+          @files[file_name]
+        end
       end
 
       def exists_with_content?(file_name)
-        @files[file_name].to_s.size > 0
+        @mutex.synchronize do
+          @files[file_name].to_s.size > 0
+        end
       end
 
       # TODO: test me
       def []=(file_name, content)
         directory = File.dirname(file_name)
         FileUtils.mkdir_p directory unless File.exist?(directory)
         File.open(file_name, 'w') { |f| f.write content }
-        @files[file_name] = content
+
+        @mutex.synchronize do
+          @files[file_name] = content
+        end
+      end
+
+      def prefetch_from(directory)
+        @threads = 20.times.map do
+          Thread.new do
+            loop do
+              file_name = @file_queue.pop
+              break if file_name == :exit
+              @mutex.synchronize do
+                @files[file_name] = File.read(file_name)
+              end
+            end
+          end
+        end
+
+        Dir["#{directory}/**/*.yml"].each do |file_name|
+          @file_queue << file_name
+        end
+
+        20.times { @file_queue << :exit }
       end
     end
   end

lib/vcr/configuration.rb

@@ -25,6 +25,7 @@ def initialize
     def cassette_library_dir=(cassette_library_dir)
       @cassette_library_dir = cassette_library_dir
       FileUtils.mkdir_p(cassette_library_dir) if cassette_library_dir
+      VCR.cassette_cache.prefetch_from(cassette_library_dir)
     end
 
     attr_reader :default_cassette_options