1 files changed, 34 insertions, 26 deletions

diff --git a/activesupport/lib/active_support/testing/isolation.rb b/activesupport/lib/active_support/testing/isolation.rb
index aa87598926..e4f8959e7a 100644
--- a/activesupport/lib/active_support/testing/isolation.rb
+++ b/activesupport/lib/active_support/testing/isolation.rb
@@ -43,32 +43,36 @@ module ActiveSupport
     module Isolation
       require 'thread'
 
-      class ParallelEach
-        include Enumerable
-
-        # default to 2 cores
-        CORES = (ENV['TEST_CORES'] || 2).to_i
-
-        def initialize list
-          @list  = list
-          @queue = SizedQueue.new CORES
-        end
+      # Recent versions of MiniTest (such as the one shipped with Ruby 2.0) already define
+      # a ParallelEach class.
+      unless defined? ParallelEach
+        class ParallelEach
+          include Enumerable
+
+          # default to 2 cores
+          CORES = (ENV['TEST_CORES'] || 2).to_i
+
+          def initialize list
+            @list  = list
+            @queue = SizedQueue.new CORES
+          end
 
-        def grep pattern
-          self.class.new super
-        end
+          def grep pattern
+            self.class.new super
+          end
 
-        def each
-          threads = CORES.times.map {
-            Thread.new {
-              while job = @queue.pop
-                yield job
-              end
+          def each
+            threads = CORES.times.map {
+              Thread.new {
+                while job = @queue.pop
+                  yield job
+                end
+              }
             }
-          }
-          @list.each { |i| @queue << i }
-          CORES.times { @queue << nil }
-          threads.each(&:join)
+            @list.each { |i| @queue << i }
+            CORES.times { @queue << nil }
+            threads.each(&:join)
+          end
         end
       end
 
@@ -84,10 +88,14 @@ module ActiveSupport
         !ENV["NO_FORK"] && ((RbConfig::CONFIG['host_os'] !~ /mswin|mingw/) && (RUBY_PLATFORM !~ /java/))
       end
 
+      @@class_setup_mutex = Mutex.new
+
       def _run_class_setup      # class setup method should only happen in parent
-        unless defined?(@@ran_class_setup) || ENV['ISOLATION_TEST']
-          self.class.setup if self.class.respond_to?(:setup)
-          @@ran_class_setup = true
+        @@class_setup_mutex.synchronize do
+          unless defined?(@@ran_class_setup) || ENV['ISOLATION_TEST']
+            self.class.setup if self.class.respond_to?(:setup)
+            @@ran_class_setup = true
+          end
         end
       end