gistfile1.txt

diff --git a/activesupport/lib/active_support/evented_file_update_checker.rb b/activesupport/lib/active_support/evented_file_update_checker.rb
index 97e982eb05..d4c712ea96 100644
--- a/activesupport/lib/active_support/evented_file_update_checker.rb
+++ b/activesupport/lib/active_support/evented_file_update_checker.rb
@@ -52,7 +52,10 @@ def initialize(files, dirs = {}, &block)
       @pid        = Process.pid
       @boot_mutex = Mutex.new
 
-      if (@dtw = directories_to_watch).any?
+      dtw = directories_to_watch
+      @dtw, @missing = dtw.partition(&:exist?)
+
+      if dtw.any?
         # Loading listen triggers warnings. These are originated by a legit
         # usage of attr_* macros for private attributes, but adds a lot of noise
         # to our test suite. Thus, we lazy load it and disable warnings locally.
@@ -68,6 +71,7 @@ def initialize(files, dirs = {}, &block)
     end
 
     def updated?
+      if @pid != Process.pid # Unrelated in passing: skip the mutex in the common case
       @boot_mutex.synchronize do
         if @pid != Process.pid
           boot!
@@ -75,6 +79,24 @@ def updated?
           @updated.make_true
         end
       end
+      end
+
+      # Consider only checking this if it's been.. 2 seconds? since we
+      # last did
+      if @missing.any?(&:exist?)
+        @boot_mutex.synchronize do
+          appeared, @missing = @missing.partition(&:exist?)
+
+          shutdown! # TODO -- alternatively, maybe we add them to the existing Listen setup, but a full reset seems maybe easiest?
+
+          @dtw += appeared
+
+          boot!
+
+          @updated.make_true
+        end
+      end
+
       @updated.true?
     end
 
@@ -123,7 +145,7 @@ def watching?(file)
       end
 
       def directories_to_watch
-        dtw = (@files + @dirs.keys).map { |f| @ph.existing_parent(f) }
+        dtw = @files + @dirs.keys
         dtw.compact!
         dtw.uniq!