Listen earlier in EventedFileUpdateChecker

Some files like routes.rb may be very large and vary between the initialization of the app and the first request. In these scenarios if we are using a forked process we cannot rely on the files to be unchanged between when the code is booted and the listener is started. 

For that reason we start a listener on the main process immediately, when we detect that a process does not have a listener started we force the updated state to be true, so we are guaranteed to catch any changes made between the code initialization and the fork.

activesupport/lib/active_support/evented_file_update_checker.rb

@@ -13,8 +13,7 @@ module ActiveSupport
   # EventedFileUpdateChecker#execute is run or when EventedFileUpdateChecker#execute_if_updated
   # is run and there have been changes to the file system.
   #
-  # Note: To start listening to change events you must first call
-  # EventedFileUpdateChecker#updated? inside of each process.
+  # Note: Forking will cause the first call to `updated?` to return `true`.
   #
   # Example:
   #
@@ -41,10 +40,11 @@ def initialize(files, dirs = {}, &block)
         @dirs[@ph.xpath(dir)] = Array(exts).map { |ext| @ph.normalize_extension(ext) }
       end
 
-      @block    = block
-      @updated  = Concurrent::AtomicBoolean.new(false)
-      @lcsp     = @ph.longest_common_subpath(@dirs.keys)
-      @pid_hash = Concurrent::Hash.new
+      @block      = block
+      @updated    = Concurrent::AtomicBoolean.new(false)
+      @lcsp       = @ph.longest_common_subpath(@dirs.keys)
+      @pid_hash   = Concurrent::Hash.new
+      @parent_pid = Process.pid
 
       if (@dtw = directories_to_watch).any?
         # Loading listen triggers warnings. These are originated by a legit
@@ -58,6 +58,7 @@ def initialize(files, dirs = {}, &block)
           end
         end
       end
+      boot!
     end
 
     def updated?
@@ -82,6 +83,7 @@ def execute_if_updated
       def boot!
         Listen.to(*@dtw, &method(:changed)).start
         @pid_hash[Process.pid] = true
+        @updated.make_true if @parent_pid != Process.pid
       end
 
       def changed(modified, added, removed)