Publish AS::Executor and AS::Reloader APIs

These should allow external code to run blocks of user code to do
"work", at a similar unit size to a web request, without needing to get
intimate with ActionDipatch.

33 files changed, 782 insertions, 307 deletions

diff --git a/actionpack/lib/action_dispatch.rb b/actionpack/lib/action_dispatch.rb
index 1e4df07d6e..01d49475de 100644
--- a/actionpack/lib/action_dispatch.rb
+++ b/actionpack/lib/action_dispatch.rb
@@ -51,8 +51,8 @@ module ActionDispatch
     autoload :Cookies
     autoload :DebugExceptions
     autoload :ExceptionWrapper
+    autoload :Executor
     autoload :Flash
-    autoload :LoadInterlock
     autoload :ParamsParser
     autoload :PublicExceptions
     autoload :Reloader
diff --git a/actionpack/lib/action_dispatch/middleware/callbacks.rb b/actionpack/lib/action_dispatch/middleware/callbacks.rb
index f80df78582..c782779b34 100644
--- a/actionpack/lib/action_dispatch/middleware/callbacks.rb
+++ b/actionpack/lib/action_dispatch/middleware/callbacks.rb
@@ -7,7 +7,16 @@ module ActionDispatch
     define_callbacks :call
 
     class << self
-      delegate :to_prepare, :to_cleanup, :to => "ActionDispatch::Reloader"
+      def to_prepare(*args, &block)
+        ActiveSupport::Reloader.to_prepare(*args, &block)
+      end
+
+      def to_cleanup(*args, &block)
+        ActiveSupport::Reloader.to_complete(*args, &block)
+      end
+
+      deprecate to_prepare: 'use ActiveSupport::Reloader.to_prepare instead',
+        to_cleanup: 'use ActiveSupport::Reloader.to_complete instead'
 
       def before(*args, &block)
         set_callback(:call, :before, *args, &block)
diff --git a/actionpack/lib/action_dispatch/middleware/executor.rb b/actionpack/lib/action_dispatch/middleware/executor.rb
new file mode 100644
index 0000000000..06245b403b
--- /dev/null
+++ b/actionpack/lib/action_dispatch/middleware/executor.rb
@@ -0,0 +1,19 @@
+require 'rack/body_proxy'
+
+module ActionDispatch
+  class Executor
+    def initialize(app, executor)
+      @app, @executor = app, executor
+    end
+
+    def call(env)
+      state = @executor.run!
+      begin
+        response = @app.call(env)
+        returned = response << ::Rack::BodyProxy.new(response.pop) { state.complete! }
+      ensure
+        state.complete! unless returned
+      end
+    end
+  end
+end
diff --git a/actionpack/lib/action_dispatch/middleware/load_interlock.rb b/actionpack/lib/action_dispatch/middleware/load_interlock.rb
deleted file mode 100644
index 07f498319c..0000000000
--- a/actionpack/lib/action_dispatch/middleware/load_interlock.rb
+++ /dev/null
@@ -1,21 +0,0 @@
-require 'active_support/dependencies'
-require 'rack/body_proxy'
-
-module ActionDispatch
-  class LoadInterlock
-    def initialize(app)
-      @app = app
-    end
-
-    def call(env)
-      interlock = ActiveSupport::Dependencies.interlock
-      interlock.start_running
-      response = @app.call(env)
-      body = Rack::BodyProxy.new(response[2]) { interlock.done_running }
-      response[2] = body
-      response
-    ensure
-      interlock.done_running unless body
-    end
-  end
-end
diff --git a/actionpack/lib/action_dispatch/middleware/reloader.rb b/actionpack/lib/action_dispatch/middleware/reloader.rb
index af9a29eb07..e5cc588bd6 100644
--- a/actionpack/lib/action_dispatch/middleware/reloader.rb
+++ b/actionpack/lib/action_dispatch/middleware/reloader.rb
@@ -23,74 +23,36 @@ module ActionDispatch
   # middleware stack, but are executed only when <tt>ActionDispatch::Reloader.prepare!</tt>
   # or <tt>ActionDispatch::Reloader.cleanup!</tt> are called manually.
   #
-  class Reloader
-    include ActiveSupport::Callbacks
-    include ActiveSupport::Deprecation::Reporting
-
-    define_callbacks :prepare
-    define_callbacks :cleanup
-
-    # Add a prepare callback. Prepare callbacks are run before each request, prior
-    # to ActionDispatch::Callback's before callbacks.
+  class Reloader < Executor
     def self.to_prepare(*args, &block)
-      unless block_given?
-        warn "to_prepare without a block is deprecated. Please use a block"
-      end
-      set_callback(:prepare, *args, &block)
+      ActiveSupport::Reloader.to_prepare(*args, &block)
     end
 
-    # Add a cleanup callback. Cleanup callbacks are run after each request is
-    # complete (after #close is called on the response body).
     def self.to_cleanup(*args, &block)
-      unless block_given?
-        warn "to_cleanup without a block is deprecated. Please use a block"
-      end
-      set_callback(:cleanup, *args, &block)
+      ActiveSupport::Reloader.to_complete(*args, &block)
     end
 
-    # Execute all prepare callbacks.
     def self.prepare!
-      new(nil).prepare!
+      if defined? Rails.application.reloader
+        Rails.application.reloader.prepare!
+      else
+        ActiveSupport::Reloader.prepare!
+      end
     end
 
-    # Execute all cleanup callbacks.
     def self.cleanup!
-      new(nil).cleanup!
-    end
-
-    def initialize(app, condition=nil)
-      @app = app
-      @condition = condition || lambda { true }
-      @validated = true
-    end
-
-    def call(env)
-      @validated = @condition.call
-      prepare!
-
-      response = @app.call(env)
-      response[2] = ::Rack::BodyProxy.new(response[2]) { cleanup! }
-
-      response
-    rescue Exception
-      cleanup!
-      raise
-    end
-
-    def prepare! #:nodoc:
-      run_callbacks :prepare if validated?
-    end
-
-    def cleanup! #:nodoc:
-      run_callbacks :cleanup if validated?
-    ensure
-      @validated = true
+      if defined? Rails.application.reloader
+        Rails.application.reloader.reload!
+      else
+        ActiveSupport::Reloader.reload!
+      end
     end
 
-    private
-
-    def validated? #:nodoc:
-      @validated
+    class << self
+      deprecate to_prepare: 'use ActiveSupport::Reloader.to_prepare instead',
+        to_cleanup: 'use ActiveSupport::Reloader.to_complete instead',
+        prepare!: 'use Rails.application.reloader.prepare! instead',
+        cleanup!: 'use Rails.application.reloader.reload! instead of cleanup + prepare'
     end
   end
 end
diff --git a/actionpack/lib/action_dispatch/testing/integration.rb b/actionpack/lib/action_dispatch/testing/integration.rb
index f4534b4173..e871ddd289 100644
--- a/actionpack/lib/action_dispatch/testing/integration.rb
+++ b/actionpack/lib/action_dispatch/testing/integration.rb
@@ -455,17 +455,24 @@ module ActionDispatch
       def before_setup # :nodoc:
         @app = nil
         @integration_session = nil
+        @execution_context = nil
+        super
+      end
+
+      def after_teardown # :nodoc:
+        remove!
         super
       end
 
       def integration_session
-        @integration_session ||= create_session(app)
+        @integration_session ||= create_session(app).tap { @execution_context = app.respond_to?(:executor) && app.executor.run! }
       end
 
       # Reset the current session. This is useful for testing multiple sessions
       # in a single test case.
       def reset!
-        @integration_session = create_session(app)
+        remove!
+        integration_session
       end
 
       def create_session(app)
@@ -481,6 +488,8 @@ module ActionDispatch
       end
 
       def remove! # :nodoc:
+        @execution_context.complete! if @execution_context
+        @execution_context = nil
         @integration_session = nil
       end
 
diff --git a/actionpack/test/dispatch/callbacks_test.rb b/actionpack/test/dispatch/callbacks_test.rb
index 5ba76d9ab9..7b707df7f6 100644
--- a/actionpack/test/dispatch/callbacks_test.rb
+++ b/actionpack/test/dispatch/callbacks_test.rb
@@ -37,13 +37,19 @@ class DispatcherTest < ActiveSupport::TestCase
 
   def test_to_prepare_and_cleanup_delegation
     prepared = cleaned = false
-    ActionDispatch::Callbacks.to_prepare { prepared = true }
-    ActionDispatch::Callbacks.to_prepare { cleaned = true }
+    assert_deprecated do
+      ActionDispatch::Callbacks.to_prepare { prepared = true }
+      ActionDispatch::Callbacks.to_prepare { cleaned = true }
+    end
 
-    ActionDispatch::Reloader.prepare!
+    assert_deprecated do
+      ActionDispatch::Reloader.prepare!
+    end
     assert prepared
 
-    ActionDispatch::Reloader.cleanup!
+    assert_deprecated do
+      ActionDispatch::Reloader.cleanup!
+    end
     assert cleaned
   end
 
diff --git a/actionpack/test/dispatch/executor_test.rb b/actionpack/test/dispatch/executor_test.rb
new file mode 100644
index 0000000000..28bb232ecd
--- /dev/null
+++ b/actionpack/test/dispatch/executor_test.rb
@@ -0,0 +1,134 @@
+require 'abstract_unit'
+
+class ExecutorTest < ActiveSupport::TestCase
+  class MyBody < Array
+    def initialize(&block)
+      @on_close = block
+    end
+
+    def foo
+      "foo"
+    end
+
+    def bar
+      "bar"
+    end
+
+    def close
+      @on_close.call if @on_close
+    end
+  end
+
+  def test_returned_body_object_always_responds_to_close
+    body = call_and_return_body
+    assert_respond_to body, :close
+  end
+
+  def test_returned_body_object_always_responds_to_close_even_if_called_twice
+    body = call_and_return_body
+    assert_respond_to body, :close
+    body.close
+
+    body = call_and_return_body
+    assert_respond_to body, :close
+    body.close
+  end
+
+  def test_returned_body_object_behaves_like_underlying_object
+    body = call_and_return_body do
+      b = MyBody.new
+      b << "hello"
+      b << "world"
+      [200, { "Content-Type" => "text/html" }, b]
+    end
+    assert_equal 2, body.size
+    assert_equal "hello", body[0]
+    assert_equal "world", body[1]
+    assert_equal "foo", body.foo
+    assert_equal "bar", body.bar
+  end
+
+  def test_it_calls_close_on_underlying_object_when_close_is_called_on_body
+    close_called = false
+    body = call_and_return_body do
+      b = MyBody.new do
+        close_called = true
+      end
+      [200, { "Content-Type" => "text/html" }, b]
+    end
+    body.close
+    assert close_called
+  end
+
+  def test_returned_body_object_responds_to_all_methods_supported_by_underlying_object
+    body = call_and_return_body do
+      [200, { "Content-Type" => "text/html" }, MyBody.new]
+    end
+    assert_respond_to body, :size
+    assert_respond_to body, :each
+    assert_respond_to body, :foo
+    assert_respond_to body, :bar
+  end
+
+  def test_run_callbacks_are_called_before_close
+    running = false
+    executor.to_run { running = true }
+
+    body = call_and_return_body
+    assert running
+
+    running = false
+    body.close
+    assert !running
+  end
+
+  def test_complete_callbacks_are_called_on_close
+    completed = false
+    executor.to_complete { completed = true }
+
+    body = call_and_return_body
+    assert !completed
+
+    body.close
+    assert completed
+  end
+
+  def test_complete_callbacks_are_called_on_exceptions
+    completed = false
+    executor.to_complete { completed = true }
+
+    begin
+      call_and_return_body do
+        raise "error"
+      end
+    rescue
+    end
+
+    assert completed
+  end
+
+  def test_callbacks_execute_in_shared_context
+    result = false
+    executor.to_run { @in_shared_context = true }
+    executor.to_complete { result = @in_shared_context }
+
+    call_and_return_body.close
+    assert result
+    assert !defined?(@in_shared_context) # it's not in the test itself
+  end
+
+  private
+    def call_and_return_body(&block)
+      app = middleware(block || proc { [200, {}, 'response'] })
+      _, _, body = app.call({'rack.input' => StringIO.new('')})
+      body
+    end
+
+    def middleware(inner_app)
+      ActionDispatch::Executor.new(inner_app, executor)
+    end
+
+    def executor
+      @executor ||= Class.new(ActiveSupport::Executor)
+    end
+end
diff --git a/actionpack/test/dispatch/reloader_test.rb b/actionpack/test/dispatch/reloader_test.rb
index 62e8197e20..fe8a4a3a17 100644
--- a/actionpack/test/dispatch/reloader_test.rb
+++ b/actionpack/test/dispatch/reloader_test.rb
@@ -4,15 +4,17 @@ class ReloaderTest < ActiveSupport::TestCase
   Reloader = ActionDispatch::Reloader
 
   teardown do
-    Reloader.reset_callbacks :prepare
-    Reloader.reset_callbacks :cleanup
+    ActiveSupport::Reloader.reset_callbacks :prepare
+    ActiveSupport::Reloader.reset_callbacks :complete
   end
 
   def test_prepare_callbacks
     a = b = c = nil
-    Reloader.to_prepare { |*args| a = b = c = 1 }
-    Reloader.to_prepare { |*args| b = c = 2 }
-    Reloader.to_prepare { |*args| c = 3 }
+    assert_deprecated do
+      Reloader.to_prepare { |*args| a = b = c = 1 }
+      Reloader.to_prepare { |*args| b = c = 2 }
+      Reloader.to_prepare { |*args| c = 3 }
+    end
 
     # Ensure to_prepare callbacks are not run when defined
     assert_nil a || b || c
@@ -60,9 +62,15 @@ class ReloaderTest < ActiveSupport::TestCase
 
   def test_condition_specifies_when_to_reload
     i, j = 0, 0, 0, 0
-    Reloader.to_prepare { |*args| i += 1 }
-    Reloader.to_cleanup { |*args| j += 1 }
-    app = Reloader.new(lambda { |env| [200, {}, []] }, lambda { i < 3 })
+    assert_deprecated do
+      Reloader.to_prepare { |*args| i += 1 }
+      Reloader.to_cleanup { |*args| j += 1 }
+    end
+
+    x = Class.new(ActiveSupport::Reloader)
+    x.check = lambda { i < 3 }
+
+    app = Reloader.new(lambda { |env| [200, {}, []] }, x)
     5.times do
       resp = app.call({})
       resp[2].close
@@ -109,7 +117,9 @@ class ReloaderTest < ActiveSupport::TestCase
 
   def test_cleanup_callbacks_are_called_when_body_is_closed
     cleaned = false
-    Reloader.to_cleanup { cleaned = true }
+    assert_deprecated do
+      Reloader.to_cleanup { cleaned = true }
+    end
 
     body = call_and_return_body
     assert !cleaned
@@ -120,7 +130,9 @@ class ReloaderTest < ActiveSupport::TestCase
 
   def test_prepare_callbacks_arent_called_when_body_is_closed
     prepared = false
-    Reloader.to_prepare { prepared = true }
+    assert_deprecated do
+      Reloader.to_prepare { prepared = true }
+    end
 
     body = call_and_return_body
     prepared = false
@@ -131,31 +143,43 @@ class ReloaderTest < ActiveSupport::TestCase
 
   def test_manual_reloading
     prepared = cleaned = false
-    Reloader.to_prepare { prepared = true }
-    Reloader.to_cleanup { cleaned  = true }
+    assert_deprecated do
+      Reloader.to_prepare { prepared = true }
+      Reloader.to_cleanup { cleaned  = true }
+    end
 
-    Reloader.prepare!
+    assert_deprecated do
+      Reloader.prepare!
+    end
     assert prepared
     assert !cleaned
 
     prepared = cleaned = false
-    Reloader.cleanup!
-    assert !prepared
+    assert_deprecated do
+      Reloader.cleanup!
+    end
+    assert prepared
     assert cleaned
   end
 
   def test_prepend_prepare_callback
     i = 10
-    Reloader.to_prepare { i += 1 }
-    Reloader.to_prepare(:prepend => true) { i = 0 }
+    assert_deprecated do
+      Reloader.to_prepare { i += 1 }
+      Reloader.to_prepare(:prepend => true) { i = 0 }
+    end
 
-    Reloader.prepare!
+    assert_deprecated do
+      Reloader.prepare!
+    end
     assert_equal 1, i
   end
 
   def test_cleanup_callbacks_are_called_on_exceptions
     cleaned = false
-    Reloader.to_cleanup { cleaned  = true }
+    assert_deprecated do
+      Reloader.to_cleanup { cleaned  = true }
+    end
 
     begin
       call_and_return_body do
@@ -169,8 +193,11 @@ class ReloaderTest < ActiveSupport::TestCase
 
   private
     def call_and_return_body(&block)
+      x = Class.new(ActiveSupport::Reloader)
+      x.check = lambda { true }
+
       @response ||= 'response'
-      @reloader ||= Reloader.new(block || proc {[200, {}, @response]})
+      @reloader ||= Reloader.new(block || proc {[200, {}, @response]}, x)
       @reloader.call({'rack.input' => StringIO.new('')})[2]
     end
 end
diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index ab3846ae65..baa497dc98 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -137,7 +137,6 @@ module ActiveRecord
 
     eager_autoload do
       autoload :AbstractAdapter
-      autoload :ConnectionManagement, "active_record/connection_adapters/abstract/connection_pool"
     end
   end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index ccd2899489..e389d818fd 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -951,24 +951,5 @@ module ActiveRecord
         owner_to_pool && owner_to_pool[owner.name]
       end
     end
-
-    class ConnectionManagement
-      def initialize(app)
-        @app = app
-      end
-
-      def call(env)
-        testing = env['rack.test']
-
-        status, headers, body = @app.call(env)
-        proxy = ::Rack::BodyProxy.new(body) do
-          ActiveRecord::Base.clear_active_connections! unless testing
-        end
-        [status, headers, proxy]
-      rescue Exception
-        ActiveRecord::Base.clear_active_connections! unless testing
-        raise
-      end
-    end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 5ef434734a..fcc1ef9d5f 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -27,7 +27,6 @@ module ActiveRecord
 
     autoload_at 'active_record/connection_adapters/abstract/connection_pool' do
       autoload :ConnectionHandler
-      autoload :ConnectionManagement
     end
 
     autoload_under 'abstract' do
diff --git a/activerecord/lib/active_record/query_cache.rb b/activerecord/lib/active_record/query_cache.rb
index dcb2bd3d84..f451ed1764 100644
--- a/activerecord/lib/active_record/query_cache.rb
+++ b/activerecord/lib/active_record/query_cache.rb
@@ -23,34 +23,26 @@ module ActiveRecord
       end
     end
 
-    def initialize(app)
-      @app = app
-    end
-
-    def call(env)
-      connection    = ActiveRecord::Base.connection
-      enabled       = connection.query_cache_enabled
-      connection_id = ActiveRecord::Base.connection_id
-      connection.enable_query_cache!
-
-      response = @app.call(env)
-      response[2] = Rack::BodyProxy.new(response[2]) do
-        restore_query_cache_settings(connection_id, enabled)
+    def self.install_executor_hooks(executor = ActiveSupport::Executor)
+      executor.to_run do
+        connection    = ActiveRecord::Base.connection
+        enabled       = connection.query_cache_enabled
+        connection_id = ActiveRecord::Base.connection_id
+        connection.enable_query_cache!
+
+        @restore_query_cache_settings = lambda do
+          ActiveRecord::Base.connection_id = connection_id
+          ActiveRecord::Base.connection.clear_query_cache
+          ActiveRecord::Base.connection.disable_query_cache! unless enabled
+        end
       end
 
-      response
-    rescue Exception => e
-      restore_query_cache_settings(connection_id, enabled)
-      raise e
-    end
-
-    private
+      executor.to_complete do
+        @restore_query_cache_settings.call if defined?(@restore_query_cache_settings)
 
-    def restore_query_cache_settings(connection_id, enabled)
-      ActiveRecord::Base.connection_id = connection_id
-      ActiveRecord::Base.connection.clear_query_cache
-      ActiveRecord::Base.connection.disable_query_cache! unless enabled
+        # FIXME: This should be skipped when env['rack.test']
+        ActiveRecord::Base.clear_active_connections!
+      end
     end
-
   end
 end
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index f4200e96b7..4c074c93ed 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -16,12 +16,6 @@ module ActiveRecord
     config.app_generators.orm :active_record, :migration => true,
                                               :timestamps => true
 
-    config.app_middleware.insert_after ::ActionDispatch::Callbacks,
-      ActiveRecord::QueryCache
-
-    config.app_middleware.insert_after ::ActionDispatch::Callbacks,
-      ActiveRecord::ConnectionAdapters::ConnectionManagement
-
     config.action_dispatch.rescue_responses.merge!(
       'ActiveRecord::RecordNotFound'   => :not_found,
       'ActiveRecord::StaleObjectError' => :conflict,
@@ -153,11 +147,9 @@ end_warning
       end
     end
 
-    initializer "active_record.set_reloader_hooks" do |app|
-      hook = app.config.reload_classes_only_on_change ? :to_prepare : :to_cleanup
-
+    initializer "active_record.set_reloader_hooks" do
       ActiveSupport.on_load(:active_record) do
-        ActionDispatch::Reloader.send(hook) do
+        ActiveSupport::Reloader.before_class_unload do
           if ActiveRecord::Base.connected?
             ActiveRecord::Base.clear_cache!
             ActiveRecord::Base.clear_reloadable_connections!
@@ -166,6 +158,12 @@ end_warning
       end
     end
 
+    initializer "active_record.set_executor_hooks" do
+      ActiveSupport.on_load(:active_record) do
+        ActiveRecord::QueryCache.install_executor_hooks
+      end
+    end
+
     initializer "active_record.add_watchable_files" do |app|
       path = app.paths["db"].first
       config.watchable_files.concat ["#{path}/schema.rb", "#{path}/structure.sql"]
diff --git a/activerecord/test/cases/connection_management_test.rb b/activerecord/test/cases/connection_management_test.rb
index d43668e57c..c4c2c69d1c 100644
--- a/activerecord/test/cases/connection_management_test.rb
+++ b/activerecord/test/cases/connection_management_test.rb
@@ -19,7 +19,7 @@ module ActiveRecord
       def setup
         @env = {}
         @app = App.new
-        @management = ConnectionManagement.new(@app)
+        @management = middleware(@app)
 
         # make sure we have an active connection
         assert ActiveRecord::Base.connection
@@ -27,17 +27,12 @@ module ActiveRecord
       end
 
       def test_app_delegation
-        manager = ConnectionManagement.new(@app)
+        manager = middleware(@app)
 
         manager.call @env
         assert_equal [@env], @app.calls
       end
 
-      def test_connections_are_active_after_call
-        @management.call(@env)
-        assert ActiveRecord::Base.connection_handler.active_connections?
-      end
-
       def test_body_responds_to_each
         _, _, body = @management.call(@env)
         bits = []
@@ -52,45 +47,40 @@ module ActiveRecord
       end
 
       def test_active_connections_are_not_cleared_on_body_close_during_test
-        @env['rack.test'] = true
-        _, _, body = @management.call(@env)
-        body.close
-        assert ActiveRecord::Base.connection_handler.active_connections?
+        executor.wrap do
+          _, _, body = @management.call(@env)
+          body.close
+          assert ActiveRecord::Base.connection_handler.active_connections?
+        end
       end
 
       def test_connections_closed_if_exception
         app       = Class.new(App) { def call(env); raise NotImplementedError; end }.new
-        explosive = ConnectionManagement.new(app)
+        explosive = middleware(app)
         assert_raises(NotImplementedError) { explosive.call(@env) }
         assert !ActiveRecord::Base.connection_handler.active_connections?
       end
 
       def test_connections_not_closed_if_exception_and_test
-        @env['rack.test'] = true
-        app               = Class.new(App) { def call(env); raise; end }.new
-        explosive         = ConnectionManagement.new(app)
-        assert_raises(RuntimeError) { explosive.call(@env) }
-        assert ActiveRecord::Base.connection_handler.active_connections?
-      end
-
-      def test_connections_closed_if_exception_and_explicitly_not_test
-        @env['rack.test'] = false
-        app       = Class.new(App) { def call(env); raise NotImplementedError; end }.new
-        explosive = ConnectionManagement.new(app)
-        assert_raises(NotImplementedError) { explosive.call(@env) }
-        assert !ActiveRecord::Base.connection_handler.active_connections?
+        executor.wrap do
+          app               = Class.new(App) { def call(env); raise; end }.new
+          explosive         = middleware(app)
+          assert_raises(RuntimeError) { explosive.call(@env) }
+          assert ActiveRecord::Base.connection_handler.active_connections?
+        end
       end
 
       test "doesn't clear active connections when running in a test case" do
-        @env['rack.test'] = true
-        @management.call(@env)
-        assert ActiveRecord::Base.connection_handler.active_connections?
+        executor.wrap do
+          @management.call(@env)
+          assert ActiveRecord::Base.connection_handler.active_connections?
+        end
       end
 
       test "proxy is polite to its body and responds to it" do
         body = Class.new(String) { def to_path; "/path"; end }.new
         app = lambda { |_| [200, {}, body] }
-        response_body = ConnectionManagement.new(app).call(@env)[2]
+        response_body = middleware(app).call(@env)[2]
         assert response_body.respond_to?(:to_path)
         assert_equal "/path", response_body.to_path
       end
@@ -98,9 +88,23 @@ module ActiveRecord
       test "doesn't mutate the original response" do
         original_response = [200, {}, 'hi']
         app = lambda { |_| original_response }
-        ConnectionManagement.new(app).call(@env)[2]
+        middleware(app).call(@env)[2]
         assert_equal 'hi', original_response.last
       end
+
+      private
+        def executor
+          @executor ||= Class.new(ActiveSupport::Executor).tap do |exe|
+            ActiveRecord::QueryCache.install_executor_hooks(exe)
+          end
+        end
+
+        def middleware(app)
+          lambda do |env|
+            a, b, c = executor.wrap { app.call(env) }
+            [a, b, Rack::BodyProxy.new(c) { }]
+          end
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/query_cache_test.rb b/activerecord/test/cases/query_cache_test.rb
index d84653e4c9..e53239cdee 100644
--- a/activerecord/test/cases/query_cache_test.rb
+++ b/activerecord/test/cases/query_cache_test.rb
@@ -16,7 +16,7 @@ class QueryCacheTest < ActiveRecord::TestCase
   def test_exceptional_middleware_clears_and_disables_cache_on_error
     assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache off'
 
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+    mw = middleware { |env|
       Task.find 1
       Task.find 1
       assert_equal 1, ActiveRecord::Base.connection.query_cache.length
@@ -31,7 +31,7 @@ class QueryCacheTest < ActiveRecord::TestCase
   def test_exceptional_middleware_leaves_enabled_cache_alone
     ActiveRecord::Base.connection.enable_query_cache!
 
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+    mw = middleware { |env|
       raise "lol borked"
     }
     assert_raises(RuntimeError) { mw.call({}) }
@@ -42,7 +42,7 @@ class QueryCacheTest < ActiveRecord::TestCase
   def test_exceptional_middleware_assigns_original_connection_id_on_error
     connection_id = ActiveRecord::Base.connection_id
 
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+    mw = middleware { |env|
       ActiveRecord::Base.connection_id = self.object_id
       raise "lol borked"
     }
@@ -53,7 +53,7 @@ class QueryCacheTest < ActiveRecord::TestCase
 
   def test_middleware_delegates
     called = false
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+    mw = middleware { |env|
       called = true
       [200, {}, nil]
     }
@@ -62,7 +62,7 @@ class QueryCacheTest < ActiveRecord::TestCase
   end
 
   def test_middleware_caches
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+    mw = middleware { |env|
       Task.find 1
       Task.find 1
       assert_equal 1, ActiveRecord::Base.connection.query_cache.length
@@ -74,50 +74,13 @@ class QueryCacheTest < ActiveRecord::TestCase
   def test_cache_enabled_during_call
     assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache off'
 
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+    mw = middleware { |env|
       assert ActiveRecord::Base.connection.query_cache_enabled, 'cache on'
       [200, {}, nil]
     }
     mw.call({})
   end
 
-  def test_cache_on_during_body_write
-    streaming = Class.new do
-      def each
-        yield ActiveRecord::Base.connection.query_cache_enabled
-      end
-    end
-
-    mw = ActiveRecord::QueryCache.new lambda { |env|
-      [200, {}, streaming.new]
-    }
-    body = mw.call({}).last
-    body.each { |x| assert x, 'cache should be on' }
-    body.close
-    assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache disabled'
-  end
-
-  def test_cache_off_after_close
-    mw = ActiveRecord::QueryCache.new lambda { |env| [200, {}, nil] }
-    body = mw.call({}).last
-
-    assert ActiveRecord::Base.connection.query_cache_enabled, 'cache enabled'
-    body.close
-    assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache disabled'
-  end
-
-  def test_cache_clear_after_close
-    mw = ActiveRecord::QueryCache.new lambda { |env|
-      Post.first
-      [200, {}, nil]
-    }
-    body = mw.call({}).last
-
-    assert !ActiveRecord::Base.connection.query_cache.empty?, 'cache not empty'
-    body.close
-    assert ActiveRecord::Base.connection.query_cache.empty?, 'cache should be empty'
-  end
-
   def test_cache_passing_a_relation
     post = Post.first
     Post.cache do
@@ -244,6 +207,13 @@ class QueryCacheTest < ActiveRecord::TestCase
       assert_equal 0, Post.where(title: 'rollback').to_a.count
     end
   end
+
+  private
+    def middleware(&app)
+      executor = Class.new(ActiveSupport::Executor)
+      ActiveRecord::QueryCache.install_executor_hooks executor
+      lambda { |env| executor.wrap { app.call(env) } }
+    end
 end
 
 class QueryCacheExpiryTest < ActiveRecord::TestCase
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 1a169d36be..28ce293bce 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Publish ActiveSupport::Executor and ActiveSupport::Reloader APIs to allow
+    components and libraries to manage, and participate in, the execution of
+    application code, and the application reloading process.
+
+    *Matthew Draper*
+
+
 ## Rails 5.0.0.beta3 (February 24, 2016) ##
 
 *   Deprecate arguments on `assert_nothing_raised`.
diff --git a/activesupport/lib/active_support.rb b/activesupport/lib/active_support.rb
index 94fe893149..72777baecd 100644
--- a/activesupport/lib/active_support.rb
+++ b/activesupport/lib/active_support.rb
@@ -33,10 +33,13 @@ module ActiveSupport
   autoload :Concern
   autoload :Dependencies
   autoload :DescendantsTracker
+  autoload :ExecutionWrapper
+  autoload :Executor
   autoload :FileUpdateChecker
   autoload :EventedFileUpdateChecker
   autoload :LogSubscriber
   autoload :Notifications
+  autoload :Reloader
 
   eager_autoload do
     autoload :BacktraceCleaner
diff --git a/activesupport/lib/active_support/dependencies/interlock.rb b/activesupport/lib/active_support/dependencies/interlock.rb
index 47bcecbb35..f1865ca2f8 100644
--- a/activesupport/lib/active_support/dependencies/interlock.rb
+++ b/activesupport/lib/active_support/dependencies/interlock.rb
@@ -19,14 +19,12 @@ module ActiveSupport #:nodoc:
         end
       end
 
-      # Attempt to obtain an "unloading" (exclusive) lock. If possible,
-      # execute the supplied block while holding the lock. If there is
-      # concurrent activity, return immediately (without executing the
-      # block) instead of waiting.
-      def attempt_unloading
-        @lock.exclusive(purpose: :unload, compatible: [:load, :unload], after_compatible: [:load, :unload], no_wait: true) do
-          yield
-        end
+      def start_unloading
+        @lock.start_exclusive(purpose: :unload, compatible: [:load, :unload])
+      end
+
+      def done_unloading
+        @lock.stop_exclusive(compatible: [:load, :unload])
       end
 
       def start_running
diff --git a/activesupport/lib/active_support/evented_file_update_checker.rb b/activesupport/lib/active_support/evented_file_update_checker.rb
index 315be85fb3..63f4f7e277 100644
--- a/activesupport/lib/active_support/evented_file_update_checker.rb
+++ b/activesupport/lib/active_support/evented_file_update_checker.rb
@@ -37,6 +37,7 @@ module ActiveSupport
 
     def execute_if_updated
       if updated?
+        yield if block_given?
         execute
         true
       end
diff --git a/activesupport/lib/active_support/execution_wrapper.rb b/activesupport/lib/active_support/execution_wrapper.rb
new file mode 100644
index 0000000000..e784556abf
--- /dev/null
+++ b/activesupport/lib/active_support/execution_wrapper.rb
@@ -0,0 +1,69 @@
+require 'active_support/callbacks'
+
+module ActiveSupport
+  class ExecutionWrapper
+    include ActiveSupport::Callbacks
+
+    define_callbacks :run
+    define_callbacks :complete
+
+    def self.to_run(*args, &block)
+      set_callback(:run, *args, &block)
+    end
+
+    def self.to_complete(*args, &block)
+      set_callback(:complete, *args, &block)
+    end
+
+    # Run this execution.
+    #
+    # Returns an instance, whose +complete!+ method *must* be invoked
+    # after the work has been performed.
+    #
+    # Where possible, prefer +wrap+.
+    def self.run!
+      new.tap(&:run!)
+    end
+
+    # Perform the work in the supplied block as an execution.
+    def self.wrap
+      return yield if active?
+
+      state = run!
+      begin
+        yield
+      ensure
+        state.complete!
+      end
+    end
+
+    class << self # :nodoc:
+      attr_accessor :active
+    end
+
+    def self.inherited(other) # :nodoc:
+      super
+      other.active = Concurrent::Hash.new(0)
+    end
+
+    self.active = Concurrent::Hash.new(0)
+
+    def self.active? # :nodoc:
+      @active[Thread.current] > 0
+    end
+
+    def run! # :nodoc:
+      self.class.active[Thread.current] += 1
+      run_callbacks(:run)
+    end
+
+    # Complete this in-flight execution. This method *must* be called
+    # exactly once on the result of any call to +run!+.
+    #
+    # Where possible, prefer +wrap+.
+    def complete!
+      run_callbacks(:complete)
+      self.class.active.delete Thread.current if (self.class.active[Thread.current] -= 1) == 0
+    end
+  end
+end
diff --git a/activesupport/lib/active_support/executor.rb b/activesupport/lib/active_support/executor.rb
new file mode 100644
index 0000000000..602fb11a44
--- /dev/null
+++ b/activesupport/lib/active_support/executor.rb
@@ -0,0 +1,6 @@
+require 'active_support/execution_wrapper'
+
+module ActiveSupport
+  class Executor < ExecutionWrapper
+  end
+end
diff --git a/activesupport/lib/active_support/file_update_checker.rb b/activesupport/lib/active_support/file_update_checker.rb
index 1fa9335080..dc7434fcac 100644
--- a/activesupport/lib/active_support/file_update_checker.rb
+++ b/activesupport/lib/active_support/file_update_checker.rb
@@ -81,6 +81,7 @@ module ActiveSupport
     # Execute the block given if updated.
     def execute_if_updated
       if updated?
+        yield if block_given?
         execute
         true
       else
diff --git a/activesupport/lib/active_support/i18n_railtie.rb b/activesupport/lib/active_support/i18n_railtie.rb
index 82aacf3b24..6cc7c90c12 100644
--- a/activesupport/lib/active_support/i18n_railtie.rb
+++ b/activesupport/lib/active_support/i18n_railtie.rb
@@ -64,8 +64,8 @@ module I18n
       end
 
       app.reloaders << reloader
-      ActionDispatch::Reloader.to_prepare do
-        reloader.execute_if_updated
+      app.reloader.to_run do
+        reloader.execute_if_updated { require_unload_lock! }
         # TODO: remove the following line as soon as the return value of
         # callbacks is ignored, that is, returning `false` does not
         # display a deprecation warning or halts the callback chain.
diff --git a/activesupport/lib/active_support/reloader.rb b/activesupport/lib/active_support/reloader.rb
new file mode 100644
index 0000000000..639b987ba8
--- /dev/null
+++ b/activesupport/lib/active_support/reloader.rb
@@ -0,0 +1,126 @@
+require 'active_support/execution_wrapper'
+
+module ActiveSupport
+  #--
+  # This class defines several callbacks:
+  #
+  #   to_prepare -- Run once at application startup, and also from
+  #   +to_run+.
+  #
+  #   to_run -- Run before a work run that is reloading. If
+  #   +reload_classes_only_on_change+ is true (the default), the class
+  #   unload will have already occurred.
+  #
+  #   to_complete -- Run after a work run that has reloaded. If
+  #   +reload_classes_only_on_change+ is false, the class unload will
+  #   have occurred after the work run, but before this callback.
+  #
+  #   before_class_unload -- Run immediately before the classes are
+  #   unloaded.
+  #
+  #   after_class_unload -- Run immediately after the classes are
+  #   unloaded.
+  #
+  class Reloader < ExecutionWrapper
+    Null = Class.new(ExecutionWrapper) # :nodoc:
+
+    define_callbacks :prepare
+
+    define_callbacks :class_unload
+
+    def self.to_prepare(*args, &block)
+      set_callback(:prepare, *args, &block)
+    end
+
+    def self.before_class_unload(*args, &block)
+      set_callback(:class_unload, *args, &block)
+    end
+
+    def self.after_class_unload(*args, &block)
+      set_callback(:class_unload, :after, *args, &block)
+    end
+
+    to_run(:after) { self.class.prepare! }
+
+    # Initiate a manual reload
+    def self.reload!
+      executor.wrap do
+        new.tap(&:run!).complete!
+      end
+      prepare!
+    end
+
+    def self.run! # :nodoc:
+      if check!
+        super
+      else
+        Null.run!
+      end
+    end
+
+    # Run the supplied block as a work unit, reloading code as needed
+    def self.wrap
+      executor.wrap do
+        super
+      end
+    end
+
+    class << self
+      attr_accessor :executor
+      attr_accessor :check
+    end
+    self.executor = Executor
+    self.check = lambda { false }
+
+    def self.check! # :nodoc:
+      @should_reload ||= check.call
+    end
+
+    def self.reloaded! # :nodoc:
+      @should_reload = false
+    end
+
+    def self.prepare! # :nodoc:
+      new.run_callbacks(:prepare)
+    end
+
+    def initialize
+      super
+      @locked = false
+    end
+
+    # Acquire the ActiveSupport::Dependencies::Interlock unload lock,
+    # ensuring it will be released automatically
+    def require_unload_lock!
+      unless @locked
+        ActiveSupport::Dependencies.interlock.start_unloading
+        @locked = true
+      end
+    end
+
+    # Release the unload lock if it has been previously obtained
+    def release_unload_lock!
+      if @locked
+        @locked = false
+        ActiveSupport::Dependencies.interlock.done_unloading
+      end
+    end
+
+    def run! # :nodoc:
+      super
+      release_unload_lock!
+    end
+
+    def class_unload!(&block) # :nodoc:
+      require_unload_lock!
+      run_callbacks(:class_unload, &block)
+    end
+
+    def complete! # :nodoc:
+      super
+      self.class.reloaded!
+    ensure
+      release_unload_lock!
+    end
+  end
+end
diff --git a/activesupport/test/executor_test.rb b/activesupport/test/executor_test.rb
new file mode 100644
index 0000000000..6db6db4fa8
--- /dev/null
+++ b/activesupport/test/executor_test.rb
@@ -0,0 +1,76 @@
+require 'abstract_unit'
+
+class ExecutorTest < ActiveSupport::TestCase
+  def test_wrap_invokes_callbacks
+    called = []
+    executor.to_run { called << :run }
+    executor.to_complete { called << :complete }
+
+    executor.wrap do
+      called << :body
+    end
+
+    assert_equal [:run, :body, :complete], called
+  end
+
+  def test_callbacks_share_state
+    result = false
+    executor.to_run { @foo = true }
+    executor.to_complete { result = @foo }
+
+    executor.wrap { }
+
+    assert result
+  end
+
+  def test_separated_calls_invoke_callbacks
+    called = []
+    executor.to_run { called << :run }
+    executor.to_complete { called << :complete }
+
+    state = executor.run!
+    called << :body
+    state.complete!
+
+    assert_equal [:run, :body, :complete], called
+  end
+
+  def test_avoids_double_wrapping
+    called = []
+    executor.to_run { called << :run }
+    executor.to_complete { called << :complete }
+
+    executor.wrap do
+      called << :early
+      executor.wrap do
+        called << :body
+      end
+      called << :late
+    end
+
+    assert_equal [:run, :early, :body, :late, :complete], called
+  end
+
+  def test_separate_classes_can_wrap
+    other_executor = Class.new(ActiveSupport::Executor)
+
+    called = []
+    executor.to_run { called << :run }
+    executor.to_complete { called << :complete }
+    other_executor.to_run { called << :other_run }
+    other_executor.to_complete { called << :other_complete }
+
+    executor.wrap do
+      other_executor.wrap do
+        called << :body
+      end
+    end
+
+    assert_equal [:run, :other_run, :body, :other_complete, :complete], called
+  end
+
+  private
+    def executor
+      @executor ||= Class.new(ActiveSupport::Executor)
+    end
+end
diff --git a/activesupport/test/reloader_test.rb b/activesupport/test/reloader_test.rb
new file mode 100644
index 0000000000..958cb49993
--- /dev/null
+++ b/activesupport/test/reloader_test.rb
@@ -0,0 +1,85 @@
+require 'abstract_unit'
+
+class ReloaderTest < ActiveSupport::TestCase
+  def test_prepare_callback
+    prepared = false
+    reloader.to_prepare { prepared = true }
+
+    assert !prepared
+    reloader.prepare!
+    assert prepared
+
+    prepared = false
+    reloader.wrap do
+      assert prepared
+      prepared = false
+    end
+    assert !prepared
+  end
+
+  def test_only_run_when_check_passes
+    r = new_reloader { true }
+    invoked = false
+    r.to_run { invoked = true }
+    r.wrap { }
+    assert invoked
+
+    r = new_reloader { false }
+    invoked = false
+    r.to_run { invoked = true }
+    r.wrap { }
+    assert !invoked
+  end
+
+  def test_full_reload_sequence
+    called = []
+    reloader.to_prepare { called << :prepare }
+    reloader.to_run { called << :reloader_run }
+    reloader.to_complete { called << :reloader_complete }
+    reloader.executor.to_run { called << :executor_run }
+    reloader.executor.to_complete { called << :executor_complete }
+
+    reloader.wrap { }
+    assert_equal [:executor_run, :reloader_run, :prepare, :reloader_complete, :executor_complete], called
+
+    called = []
+    reloader.reload!
+    assert_equal [:executor_run, :reloader_run, :prepare, :reloader_complete, :executor_complete, :prepare], called
+
+    reloader.check = lambda { false }
+
+    called = []
+    reloader.wrap { }
+    assert_equal [:executor_run, :executor_complete], called
+
+    called = []
+    reloader.reload!
+    assert_equal [:executor_run, :reloader_run, :prepare, :reloader_complete, :executor_complete, :prepare], called
+  end
+
+  def test_class_unload_block
+    called = []
+    reloader.before_class_unload { called << :before_unload }
+    reloader.after_class_unload { called << :after_unload }
+    reloader.to_run do
+      class_unload! do
+        called << :unload
+      end
+    end
+    reloader.wrap { called << :body }
+
+    assert_equal [:before_unload, :unload, :after_unload, :body], called
+  end
+
+  private
+    def new_reloader(&check)
+      Class.new(ActiveSupport::Reloader).tap do |r|
+        r.check = check
+        r.executor = Class.new(ActiveSupport::Executor)
+      end
+    end
+
+    def reloader
+      @reloader ||= new_reloader { true }
+    end
+end
diff --git a/railties/lib/rails/application.rb b/railties/lib/rails/application.rb
index bff33ff42e..d05d610ee1 100644
--- a/railties/lib/rails/application.rb
+++ b/railties/lib/rails/application.rb
@@ -113,7 +113,7 @@ module Rails
 
     attr_accessor :assets, :sandbox
     alias_method :sandbox?, :sandbox
-    attr_reader :reloaders
+    attr_reader :reloaders, :reloader, :executor
 
     delegate :default_url_options, :default_url_options=, to: :routes
 
@@ -131,6 +131,10 @@ module Rails
       @message_verifiers = {}
       @ran_load_hooks    = false
 
+      @executor          = Class.new(ActiveSupport::Executor)
+      @reloader          = Class.new(ActiveSupport::Reloader)
+      @reloader.executor = @executor
+
       # are these actually used?
       @initial_variable_values = initial_variable_values
       @block = block
diff --git a/railties/lib/rails/application/default_middleware_stack.rb b/railties/lib/rails/application/default_middleware_stack.rb
index 4f1cc0703d..381e548730 100644
--- a/railties/lib/rails/application/default_middleware_stack.rb
+++ b/railties/lib/rails/application/default_middleware_stack.rb
@@ -34,22 +34,10 @@ module Rails
             # handling: presumably their code is not threadsafe
 
             middleware.use ::Rack::Lock
-
-          elsif config.allow_concurrency == :unsafe
-            # Do nothing, even if we know this is dangerous. This is the
-            # historical behaviour for true.
-
-          else
-            # Default concurrency setting: enabled, but safe
-
-            unless config.cache_classes && config.eager_load
-              # Without cache_classes + eager_load, the load interlock
-              # is required for proper operation
-
-              middleware.use ::ActionDispatch::LoadInterlock
-            end
           end
 
+          middleware.use ::ActionDispatch::Executor, app.executor
+
           middleware.use ::Rack::Runtime
           middleware.use ::Rack::MethodOverride unless config.api_only
           middleware.use ::ActionDispatch::RequestId
@@ -61,7 +49,7 @@ module Rails
           middleware.use ::ActionDispatch::RemoteIp, config.action_dispatch.ip_spoofing_check, config.action_dispatch.trusted_proxies
 
           unless config.cache_classes
-            middleware.use ::ActionDispatch::Reloader, lambda { reload_dependencies? }
+            middleware.use ::ActionDispatch::Reloader, app.reloader
           end
 
           middleware.use ::ActionDispatch::Callbacks
@@ -83,10 +71,6 @@ module Rails
 
       private
 
-        def reload_dependencies?
-          config.reload_classes_only_on_change != true || app.reloaders.map(&:updated?).any?
-        end
-
         def load_rack_cache
           rack_cache = config.action_dispatch.rack_cache
           return unless rack_cache
diff --git a/railties/lib/rails/application/finisher.rb b/railties/lib/rails/application/finisher.rb
index 64ec539564..34f2265108 100644
--- a/railties/lib/rails/application/finisher.rb
+++ b/railties/lib/rails/application/finisher.rb
@@ -38,16 +38,16 @@ module Rails
         app.routes.define_mounted_helper(:main_app)
       end
 
-      initializer :add_to_prepare_blocks do
+      initializer :add_to_prepare_blocks do |app|
         config.to_prepare_blocks.each do |block|
-          ActionDispatch::Reloader.to_prepare(&block)
+          app.reloader.to_prepare(&block)
         end
       end
 
       # This needs to happen before eager load so it happens
       # in exactly the same point regardless of config.cache_classes
-      initializer :run_prepare_callbacks do
-        ActionDispatch::Reloader.prepare!
+      initializer :run_prepare_callbacks do |app|
+        app.reloader.prepare!
       end
 
       initializer :eager_load! do
@@ -62,13 +62,47 @@ module Rails
         ActiveSupport.run_load_hooks(:after_initialize, self)
       end
 
+      initializer :configure_executor_for_concurrency do |app|
+        if config.allow_concurrency == false
+          # User has explicitly opted out of concurrent request
+          # handling: presumably their code is not threadsafe
+
+          mutex = Mutex.new
+          app.executor.to_run(prepend: true) do
+            mutex.lock
+          end
+          app.executor.to_complete(:after) do
+            mutex.unlock
+          end
+
+        elsif config.allow_concurrency == :unsafe
+          # Do nothing, even if we know this is dangerous. This is the
+          # historical behaviour for true.
+
+        else
+          # Default concurrency setting: enabled, but safe
+
+          unless config.cache_classes && config.eager_load
+            # Without cache_classes + eager_load, the load interlock
+            # is required for proper operation
+
+            app.executor.to_run(prepend: true) do
+              ActiveSupport::Dependencies.interlock.start_running
+            end
+            app.executor.to_complete(:after) do
+              ActiveSupport::Dependencies.interlock.done_running
+            end
+          end
+        end
+      end
+
       # Set routes reload after the finisher hook to ensure routes added in
       # the hook are taken into account.
-      initializer :set_routes_reloader_hook do
+      initializer :set_routes_reloader_hook do |app|
         reloader = routes_reloader
         reloader.execute_if_updated
         self.reloaders << reloader
-        ActionDispatch::Reloader.to_prepare do
+        app.reloader.to_run do
           # We configure #execute rather than #execute_if_updated because if
           # autoloaded constants are cleared we need to reload routes also in
           # case any was used there, as in
@@ -78,18 +112,27 @@ module Rails
           # This means routes are also reloaded if i18n is updated, which
           # might not be necessary, but in order to be more precise we need
           # some sort of reloaders dependency support, to be added.
+          require_unload_lock!
           reloader.execute
         end
       end
 
       # Set clearing dependencies after the finisher hook to ensure paths
       # added in the hook are taken into account.
-      initializer :set_clear_dependencies_hook, group: :all do
+      initializer :set_clear_dependencies_hook, group: :all do |app|
         callback = lambda do
-          ActiveSupport::Dependencies.interlock.unloading do
-            ActiveSupport::DescendantsTracker.clear
-            ActiveSupport::Dependencies.clear
+          ActiveSupport::DescendantsTracker.clear
+          ActiveSupport::Dependencies.clear
+        end
+
+        if config.cache_classes
+          app.reloader.check = lambda { false }
+        elsif config.reload_classes_only_on_change
+          app.reloader.check = lambda do
+            app.reloaders.map(&:updated?).any?
           end
+        else
+          app.reloader.check = lambda { true }
         end
 
         if config.reload_classes_only_on_change
@@ -99,15 +142,19 @@ module Rails
           # Prepend this callback to have autoloaded constants cleared before
           # any other possible reloading, in case they need to autoload fresh
           # constants.
-          ActionDispatch::Reloader.to_prepare(prepend: true) do
+          app.reloader.to_run(prepend: true) do
             # In addition to changes detected by the file watcher, if routes
             # or i18n have been updated we also need to clear constants,
             # that's why we run #execute rather than #execute_if_updated, this
             # callback has to clear autoloaded constants after any update.
-            reloader.execute
+            class_unload! do
+              reloader.execute
+            end
           end
         else
-          ActionDispatch::Reloader.to_cleanup(&callback)
+          app.reloader.to_complete do
+            class_unload!(&callback)
+          end
         end
       end
 
diff --git a/railties/lib/rails/console/app.rb b/railties/lib/rails/console/app.rb
index ac5836a588..9ad77e0a80 100644
--- a/railties/lib/rails/console/app.rb
+++ b/railties/lib/rails/console/app.rb
@@ -29,8 +29,7 @@ module Rails
     # reloads the environment
     def reload!(print=true)
       puts "Reloading..." if print
-      ActionDispatch::Reloader.cleanup!
-      ActionDispatch::Reloader.prepare!
+      Rails.application.reloader.reload!
       true
     end
   end
diff --git a/railties/test/application/console_test.rb b/railties/test/application/console_test.rb
index 7bf123d12b..ea68e63f8f 100644
--- a/railties/test/application/console_test.rb
+++ b/railties/test/application/console_test.rb
@@ -52,12 +52,11 @@ class ConsoleTest < ActiveSupport::TestCase
     a = b = c = nil
 
     # TODO: These should be defined on the initializer
-    ActionDispatch::Reloader.to_cleanup { a = b = c = 1 }
-    ActionDispatch::Reloader.to_cleanup { b = c = 2 }
-    ActionDispatch::Reloader.to_prepare { c = 3 }
+    ActiveSupport::Reloader.to_complete { a = b = c = 1 }
+    ActiveSupport::Reloader.to_complete { b = c = 2 }
+    ActiveSupport::Reloader.to_prepare { c = 3 }
 
-    # Hide Reloading... output
-    silence_stream(STDOUT) { irb_context.reload! }
+    irb_context.reload!(false)
 
     assert_equal 1, a
     assert_equal 2, b
@@ -81,7 +80,7 @@ class ConsoleTest < ActiveSupport::TestCase
     MODEL
 
     assert !User.new.respond_to?(:age)
-    silence_stream(STDOUT) { irb_context.reload! }
+    irb_context.reload!(false)
     assert User.new.respond_to?(:age)
   end
 
diff --git a/railties/test/application/middleware_test.rb b/railties/test/application/middleware_test.rb
index 1434522cce..5869ff64bc 100644
--- a/railties/test/application/middleware_test.rb
+++ b/railties/test/application/middleware_test.rb
@@ -26,7 +26,7 @@ module ApplicationTests
       assert_equal [
         "Rack::Sendfile",
         "ActionDispatch::Static",
-        "ActionDispatch::LoadInterlock",
+        "ActionDispatch::Executor",
         "ActiveSupport::Cache::Strategy::LocalCache",
         "Rack::Runtime",
         "Rack::MethodOverride",
@@ -38,8 +38,6 @@ module ApplicationTests
         "ActionDispatch::Reloader",
         "ActionDispatch::Callbacks",
         "ActiveRecord::Migration::CheckPending",
-        "ActiveRecord::ConnectionAdapters::ConnectionManagement",
-        "ActiveRecord::QueryCache",
         "ActionDispatch::Cookies",
         "ActionDispatch::Session::CookieStore",
         "ActionDispatch::Flash",
@@ -57,7 +55,7 @@ module ApplicationTests
       assert_equal [
         "Rack::Sendfile",
         "ActionDispatch::Static",
-        "ActionDispatch::LoadInterlock",
+        "ActionDispatch::Executor",
         "ActiveSupport::Cache::Strategy::LocalCache",
         "Rack::Runtime",
         "ActionDispatch::RequestId",
@@ -67,8 +65,6 @@ module ApplicationTests
         "ActionDispatch::RemoteIp",
         "ActionDispatch::Reloader",
         "ActionDispatch::Callbacks",
-        "ActiveRecord::ConnectionAdapters::ConnectionManagement",
-        "ActiveRecord::QueryCache",
         "Rack::Head",
         "Rack::ConditionalGet",
         "Rack::ETag"
@@ -114,23 +110,12 @@ module ApplicationTests
     test "removing Active Record omits its middleware" do
       use_frameworks []
       boot!
-      assert !middleware.include?("ActiveRecord::ConnectionAdapters::ConnectionManagement")
-      assert !middleware.include?("ActiveRecord::QueryCache")
       assert !middleware.include?("ActiveRecord::Migration::CheckPending")
     end
 
-    test "includes interlock if cache_classes is set but eager_load is not" do
-      add_to_config "config.cache_classes = true"
-      boot!
-      assert_not_includes middleware, "Rack::Lock"
-      assert_includes middleware, "ActionDispatch::LoadInterlock"
-    end
-
-    test "includes interlock if cache_classes is off" do
-      add_to_config "config.cache_classes = false"
+    test "includes executor" do
       boot!
-      assert_not_includes middleware, "Rack::Lock"
-      assert_includes middleware, "ActionDispatch::LoadInterlock"
+      assert_includes middleware, "ActionDispatch::Executor"
     end
 
     test "does not include lock if cache_classes is set and so is eager_load" do
@@ -138,21 +123,18 @@ module ApplicationTests
       add_to_config "config.eager_load = true"
       boot!
       assert_not_includes middleware, "Rack::Lock"
-      assert_not_includes middleware, "ActionDispatch::LoadInterlock"
     end
 
     test "does not include lock if allow_concurrency is set to :unsafe" do
       add_to_config "config.allow_concurrency = :unsafe"
       boot!
       assert_not_includes middleware, "Rack::Lock"
-      assert_not_includes middleware, "ActionDispatch::LoadInterlock"
     end
 
     test "includes lock if allow_concurrency is disabled" do
       add_to_config "config.allow_concurrency = false"
       boot!
       assert_includes middleware, "Rack::Lock"
-      assert_not_includes middleware, "ActionDispatch::LoadInterlock"
     end
 
     test "removes static asset server if public_file_server.enabled is disabled" do