Rails::Subscriber is now responsible for flushing all loggers it's responsible for.

railties/lib/rails/subscriber.rb

@@ -30,7 +30,8 @@ module Rails
   # purposes(which slows down the main thread). Besides of providing a centralized
   # facility on top of Rails.logger.
   # 
-  # Finally, Subscriber some helpers to deal with logging, like managing console colors.
+  # 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
     self.colorize_logging = true
@@ -64,6 +65,15 @@ module Rails
       if subscriber.respond_to?(name) && subscriber.logger
         subscriber.send(name, ActiveSupport::Notifications::Event.new(*args))
       end
+
+      flush_all! if args[0] == "action_dispatch.callback"
+    end
+
+    # Flush all subscribers' logger.
+    def self.flush_all!
+      loggers = subscribers.values.map(&:logger)
+      loggers.uniq!
+      loggers.each { |l| l.flush if l.respond_to?(:flush) }
     end
 
     # By default, we use the Rails.logger for logging.

railties/lib/rails/subscriber/test_helper.rb

@@ -58,7 +58,10 @@ module Rails
       end
 
       class MockLogger
+        attr_reader :flush_count
+
         def initialize
+          @flush_count = 0
           @logged = Hash.new { |h,k| h[k] = [] }
         end
 
@@ -69,6 +72,10 @@ module Rails
         def logged(level)
           @logged[level].compact.map { |l| l.to_s.strip }
         end
+
+        def flush
+          @flush_count += 1
+        end
       end
 
       # Wait notifications to be published.

railties/test/subscriber_test.rb

@@ -76,10 +76,31 @@ module SubscriberTest
 
   def test_does_not_send_the_event_if_logger_is_nil
     Rails.logger = nil
+    @subscriber.expects(:some_event).never
     Rails::Subscriber.add :my_subscriber, @subscriber
     instrument "my_subscriber.some_event"
     wait
-    assert_equal [], @logger.logged(:info)
+  end
+
+  def test_flushes_loggers
+    Rails::Subscriber.add :my_subscriber, @subscriber
+    Rails::Subscriber.flush_all!
+    assert_equal 1, @logger.flush_count
+  end
+
+  def test_flushes_loggers_when_action_dispatch_callback_is_received
+    Rails::Subscriber.add :my_subscriber, @subscriber
+    instrument "action_dispatch.callback"
+    wait
+    assert_equal 1, @logger.flush_count
+  end
+
+  def test_flushes_the_same_logger_just_once
+    Rails::Subscriber.add :my_subscriber, @subscriber
+    Rails::Subscriber.add :another, @subscriber
+    instrument "action_dispatch.callback"
+    wait
+    assert_equal 1, @logger.flush_count
   end
 
   class SyncSubscriberTest < ActiveSupport::TestCase