Merge pull request #670 from connamara/thread_interceptor

Fixes intermittent ConcurrencyError seen in JRuby

lib/cucumber/formatter/interceptor.rb

@@ -1,18 +1,27 @@
+require 'thread'
 
 module Cucumber
   module Formatter
     module Interceptor
       class Pipe
-        attr_reader :pipe, :buffer
+        attr_reader :pipe
         def initialize(pipe)
           @pipe = pipe
           @buffer = []
           @wrapped = true
         end
 
         def write(str)
-          @buffer << str if @wrapped
-          return @pipe.write(str)
+          lock.synchronize do 
+            @buffer << str if @wrapped
+            return @pipe.write(str)
+          end
+        end
+
+        def buffer
+          lock.synchronize do
+            return @buffer.dup
+          end
         end
 
         def unwrap!
@@ -60,6 +69,11 @@ def self.wrap(pipe)
             return $stdout
           end
         end
+
+      private
+        def lock
+          @lock||=Mutex.new
+        end
       end
     end
   end