Prefer Ruby core Mutex to our local copy

Author: pirj

.rubocop.yml

@@ -19,11 +19,6 @@ Style/EvalWithLocation:
     # eval is only used here to check syntax
     - 'lib/rspec/support/ruby_features.rb'
 
-Lint/AssignmentInCondition:
-  Exclude:
-    # The pattern makes sense here
-    - 'lib/rspec/support/mutex.rb'
-
 # Over time we'd like to get this down, but this is what we're at now.
 Metrics/AbcSize:
   Max: 22

lib/rspec/support/mutex.rb

@@ -6,16 +6,12 @@ module Support
     # Based on Monitor as of 2.2 -
     # https://github.com/ruby/ruby/blob/eb7ddaa3a47bf48045d26c72eb0f263a53524ebc/lib/monitor.rb#L9
     #
-    # Depends on Mutex, but Mutex is only available as part of core since 1.9.1:
-    #   exists - http://ruby-doc.org/core-1.9.1/Mutex.html
-    #   dne    - http://ruby-doc.org/core-1.9.0/Mutex.html
-    #
     # @private
     class ReentrantMutex
       def initialize
         @owner = nil
         @count = 0
-        @mutex = Mutex.new
+        @mutex = Thread::Mutex.new
       end
 
       def synchronize
@@ -40,22 +36,5 @@ def exit
         @mutex.unlock
       end
     end
-
-    if defined? ::Mutex
-      # On 1.9 and up, this is in core, so we just use the real one
-      class Mutex < ::Mutex
-        # If you mock Mutex.new you break our usage of Mutex, so
-        # instead we capture the original method to return Mutexs.
-        NEW_MUTEX_METHOD = Mutex.method(:new)
-
-        def self.new
-          NEW_MUTEX_METHOD.call
-        end
-      end
-    else # For 1.8.7
-      # :nocov:
-      RSpec::Support.require_rspec_support "mutex"
-      # :nocov:
-    end
   end
 end