LogTailer should be invoked after all logs in threads were flushed.

railties/lib/rails/commands/server.rb

@@ -46,22 +46,18 @@ def start
       trap(:INT) { exit }
       puts "=> Ctrl-C to shutdown server" unless options[:daemonize]
 
+      Rails::Subscriber.tail_log = true unless options[:daemonize]
       super
     ensure
       puts 'Exiting' unless options[:daemonize]
     end
 
     def middleware
       middlewares = []
-      middlewares << [Rails::Rack::LogTailer, log_path] unless options[:daemonize]
       middlewares << [Rails::Rack::Debugger]  if options[:debugger]
       Hash.new(middlewares)
     end
 
-    def log_path
-      "log/#{options[:environment]}.log"
-    end
-
     def default_options
       super.merge({
         :Port        => 3000,

railties/lib/rails/rack/log_tailer.rb

@@ -13,11 +13,11 @@ def initialize(app, log = nil)
 
       def call(env)
         response = @app.call(env)
-        tail_log
+        tail!
         response
       end
 
-      def tail_log
+      def tail!
         @file.seek @cursor
 
         mod = @file.mtime.to_f

railties/lib/rails/subscriber.rb

@@ -33,8 +33,9 @@ module Rails
   # Subscriber also has some helpers to deal with logging and automatically flushes
   # all logs when the request finishes (via action_dispatch.callback notification).
   class Subscriber
-    cattr_accessor :colorize_logging, :instance_writer => false
+    mattr_accessor :colorize_logging, :tail_log
     self.colorize_logging = true
+    self.tail_log = false
 
     # Embed in a String to clear all previous ANSI sequences.
     CLEAR      = "\e[0m"
@@ -58,6 +59,12 @@ def self.subscribers
       @subscribers ||= {}
     end
 
+    # Use Rails::Rack::LogTailer to do the log tailing.
+    # TODO Leave this as middleware or move inside Subscriber?
+    def self.log_tailer
+      @log_tailer ||= Rails::Rack::LogTailer.new(nil, "log/#{Rails.env}.log")
+    end
+
     def self.dispatch(args)
       namespace, name = args[0].split(".")
       subscriber = subscribers[namespace.to_sym]
@@ -66,7 +73,10 @@ def self.dispatch(args)
         subscriber.send(name, ActiveSupport::Notifications::Event.new(*args))
       end
 
-      flush_all! if args[0] == "action_dispatch.callback"
+      if args[0] == "action_dispatch.callback" && !subscribers.empty?
+        flush_all!
+        log_tailer.tail! if tail_log
+      end
     end
 
     # Flush all subscribers' logger.

railties/test/subscriber_test.rb

@@ -24,11 +24,13 @@ module SubscriberTest
   def setup
     super
     @subscriber = MySubscriber.new
+    Rails::Subscriber.instance_variable_set(:@log_tailer, nil)
   end
 
   def teardown
     super
     Rails::Subscriber.subscribers.clear
+    Rails::Subscriber.instance_variable_set(:@log_tailer, nil)
   end
 
   def instrument(*args, &block)
@@ -103,6 +105,19 @@ def test_flushes_the_same_logger_just_once
     assert_equal 1, @logger.flush_count
   end
 
+  def test_tails_logs_when_action_dispatch_callback_is_received
+    log_tailer = mock()
+    log_tailer.expects(:tail!)
+    Rails::Rack::LogTailer.expects(:new).with(nil, "log/development.log").returns(log_tailer)
+
+    Rails::Subscriber.tail_log = true
+    Rails::Subscriber.add :my_subscriber, @subscriber
+    instrument "action_dispatch.callback"
+    wait
+  ensure
+    Rails::Subscriber.tail_log = false
+  end
+
   class SyncSubscriberTest < ActiveSupport::TestCase
     include Rails::Subscriber::SyncTestHelper
     include SubscriberTest