Use Mutex from core, prevent it from being stubbed

Author: pirj

lib/rspec/support/mutex.rb

@@ -1,73 +1,11 @@
 module RSpec
   module Support
-    # On 1.8.7, it's in the stdlib.
-    # We don't want to load the stdlib, b/c this is a test tool, and can affect
-    # the test environment, causing tests to pass where they should fail.
-    #
-    # So we're transcribing/modifying it from
-    # https://github.com/ruby/ruby/blob/v1_8_7_374/lib/thread.rb#L56
-    # Some methods we don't need are deleted. Anything I don't
-    # understand (there's quite a bit, actually) is left in.
-    #
-    # Some formating changes are made to appease the robot overlord:
-    #   https://travis-ci.org/rspec/rspec-core/jobs/54410874
+    # This class protects us against Mutex.new stubbed out within tests.
     # @private
-    class Mutex
-      def initialize
-        @waiting = []
-        @locked = false
-        @waiting.taint
-        taint
+    class Mutex < ::Mutex
+      class << self
+        define_method(:new, &::Mutex.method(:new))
       end
-
-      # @private
-      def lock
-        while Thread.critical = true && @locked
-          @waiting.push Thread.current
-          Thread.stop
-        end
-        @locked = true
-        Thread.critical = false
-        self
-      end
-
-      # @private
-      def unlock
-        return unless @locked
-        Thread.critical = true
-        @locked = false
-        wakeup_and_run_waiting_thread
-        self
-      end
-
-      # @private
-      def synchronize
-        lock
-        begin
-          yield
-        ensure
-          unlock
-        end
-      end
-
-    private
-
-      def wakeup_and_run_waiting_thread
-        begin
-          t = @waiting.shift
-          t.wakeup if t
-        rescue ThreadError
-          retry
-        end
-        Thread.critical = false
-        begin
-          t.run if t
-        rescue ThreadError
-          :noop
-        end
-      end
-
-      # Avoid warnings for library wide checks spec
-    end unless defined?(::RSpec::Support::Mutex) || defined?(::Mutex)
+    end
   end
 end

lib/rspec/support/reentrant_mutex.rb

@@ -1,3 +1,5 @@
+RSpec::Support.require_rspec_support "mutex"
+
 module RSpec
   module Support
     # Allows a thread to lock out other threads from a critical section of code,
@@ -6,10 +8,6 @@ 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
@@ -40,22 +38,5 @@ 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

spec/rspec/support/mutex_spec.rb

@@ -1,7 +1,7 @@
 require 'rspec/support/mutex'
 
 RSpec.describe RSpec::Support::Mutex do
-  it "allows ::Mutex to be mocked", :if => defined?(::Mutex) do
+  it "allows ::Mutex to be mocked" do
     expect(Mutex).to receive(:new)
     ::Mutex.new
   end

spec/rspec/support/reentrant_mutex_spec.rb

@@ -2,7 +2,7 @@
 require 'thread_order'
 
 # There are no assertions specifically
-# They are pass if they don't deadlock
+# They pass if they don't deadlock
 RSpec.describe RSpec::Support::ReentrantMutex do
   let!(:mutex) { described_class.new }
   let!(:order) { ThreadOrder.new }