removes the mutex around `changed`

This method needs to ensure that if a change happens, it is going to be registered.
With this refactor suggested by @matthewd race conditions do not matter because if
no file is watched, nothing is done. And as long as some invocation sets the flag
to true, it will stay true.

The refactor leaves a race condition in which two simultaneous threads that watch
some of the files passed do the actual work in `any?`, whereas the mutex guaranteed
that was done at most once. But this is considered to be a better tradeoff.

1 files changed, 2 insertions, 7 deletions

diff --git a/activesupport/lib/active_support/file_evented_update_checker.rb b/activesupport/lib/active_support/file_evented_update_checker.rb
index fbc3fa2147..bb0f26f874 100644
--- a/activesupport/lib/active_support/file_evented_update_checker.rb
+++ b/activesupport/lib/active_support/file_evented_update_checker.rb
@@ -1,7 +1,6 @@
 require 'listen'
 require 'set'
 require 'pathname'
-require 'thread'
 require 'concurrent/atomic/atomic_boolean'
 
 module ActiveSupport
@@ -22,8 +21,6 @@ module ActiveSupport
       if (dtw = directories_to_watch).any?
         Listen.to(*dtw, &method(:changed)).start
       end
-
-      @mutex = Mutex.new
     end
 
     def updated?
@@ -45,10 +42,8 @@ module ActiveSupport
     private
 
       def changed(modified, added, removed)
-        @mutex.synchronize do
-          unless updated?
-            @updated.value = (modified + added + removed).any? { |f| watching?(f) }
-          end
+        unless updated?
+          @updated.make_true if (modified + added + removed).any? { |f| watching?(f) }
         end
       end