Controller actions are processed in a separate thread for live

responses.

Processing controller actions in a separate thread allows us to work
around the rack api - we can allow the user to set status and headers,
then block until the first bytes are written.  As soon as the first
bytes are written, the main thread can return the status, headers, and
(essentially) a queue for the body.

actionpack/lib/action_controller/metal/live.rb

@@ -6,8 +6,7 @@ module ActionController
     class Response < ActionDispatch::Response
       class Buffer < ActionDispatch::Response::Buffer # :nodoc:
         def initialize(response)
-          @response = response
-          @buf      = Queue.new
+          super(response, Queue.new)
         end
 
         def write(string)
@@ -59,5 +58,30 @@ module ActionController
         buf
       end
     end
+
+    def process(name)
+      t1 = Thread.current
+      locals = t1.keys.map { |key| [key, t1[key]] }
+
+      # This processes the action in a child thread.  It lets us return the
+      # response code and headers back up the rack stack, and still process
+      # the body in parallel with sending data to the client
+      Thread.new {
+        t2 = Thread.current
+        t2.abort_on_exception = true
+
+        # Since we're processing the view in a different thread, copy the
+        # thread locals from the main thread to the child thread. :'(
+        locals.each { |k,v| t2[k] = v }
+
+        begin
+          super(name)
+        ensure
+          @_response.commit!
+        end
+      }
+
+      @_response.await_commit
+    end
   end
 end

actionpack/lib/action_controller/test_case.rb

@@ -517,8 +517,8 @@ module ActionController
       end
 
       def setup_controller_request_and_response
-        @request          = TestRequest.new
-        @response         = TestResponse.new
+        @request          = build_request
+        @response         = build_response
         @response.request = @request
 
         @controller = nil unless defined? @controller
@@ -539,6 +539,14 @@ module ActionController
         end
       end
 
+      def build_request
+        TestRequest.new
+      end
+
+      def build_response
+        TestResponse.new
+      end
+
       included do
         include ActionController::TemplateAssertions
         include ActionDispatch::Assertions

actionpack/test/controller/live_stream_test.rb

@@ -1,16 +1,41 @@
 require 'abstract_unit'
+require 'active_support/concurrency/latch'
 
 module ActionController
-  class StreamingResponseTest < ActionController::TestCase
+  class LiveStreamTest < ActionController::TestCase
     class TestController < ActionController::Base
+      include ActionController::Live
+
+      attr_accessor :latch, :tc
+
       def self.controller_path
         'test'
       end
 
       def basic_stream
+        response.headers['Content-Type'] = 'text/event-stream'
+        %w{ hello world }.each do |word|
+          response.stream.write word
+        end
+        response.stream.close
+      end
+
+      def blocking_stream
+        response.headers['Content-Type'] = 'text/event-stream'
+        %w{ hello world }.each do |word|
+          response.stream.write word
+          latch.await
+        end
+        response.stream.close
+      end
+
+      def thread_locals
+        tc.assert_equal 'aaron', Thread.current[:setting]
+        tc.refute_equal Thread.current.object_id, Thread.current[:originating_thread]
+
+        response.headers['Content-Type'] = 'text/event-stream'
         %w{ hello world }.each do |word|
           response.stream.write word
-          response.stream.write "\n"
         end
         response.stream.close
       end
@@ -18,9 +43,50 @@ module ActionController
 
     tests TestController
 
+    class TestResponse < Live::Response
+      def recycle!
+        initialize
+      end
+    end
+
+    def build_response
+      TestResponse.new
+    end
+
     def test_write_to_stream
+      @controller = TestController.new
       get :basic_stream
-      assert_equal "hello\nworld\n", @response.body
+      assert_equal "helloworld", @response.body
+      assert_equal 'text/event-stream', @response.headers['Content-Type']
+    end
+
+    def test_async_stream
+      @controller.latch = ActiveSupport::Concurrency::Latch.new
+      parts             = ['hello', 'world']
+
+      @controller.request  = @request
+      @controller.response = @response
+
+      t = Thread.new(@response) { |resp|
+        resp.stream.each do |part|
+          assert_equal parts.shift, part
+          ol = @controller.latch
+          @controller.latch = ActiveSupport::Concurrency::Latch.new
+          ol.release
+        end
+      }
+
+      @controller.process :blocking_stream
+
+      assert t.join
+    end
+
+    def test_thread_locals_get_copied
+      @controller.tc = self
+      Thread.current[:originating_thread] = Thread.current.object_id
+      Thread.current[:setting]            = 'aaron'
+
+      get :thread_locals
     end
   end
 end