Merge pull request #36323 from jhawthorn/cache_expiry_mutex

Wrap ActionView cache expiry in a mutex

actionview/lib/action_view/cache_expiry.rb

@@ -16,18 +16,21 @@ def initialize(watcher:)
       @watched_dirs = nil
       @watcher_class = watcher
       @watcher = nil
+      @mutex = Mutex.new
     end
 
     def clear_cache_if_necessary
-      watched_dirs = dirs_to_watch
-      if watched_dirs != @watched_dirs
-        @watched_dirs = watched_dirs
-        @watcher = @watcher_class.new([], watched_dirs) do
-          clear_cache
+      @mutex.synchronize do
+        watched_dirs = dirs_to_watch
+        if watched_dirs != @watched_dirs
+          @watched_dirs = watched_dirs
+          @watcher = @watcher_class.new([], watched_dirs) do
+            clear_cache
+          end
+          @watcher.execute
+        else
+          @watcher.execute_if_updated
         end
-        @watcher.execute
-      else
-        @watcher.execute_if_updated
       end
     end