threads can wait on responses to be committed

actionpack/lib/action_controller/test_case.rb

@@ -226,6 +226,7 @@ def recycle!
       @block = nil
       @length = 0
       @body = []
+      @committed = false
       @charset = @content_type = nil
       @request = @template = nil
     end

actionpack/lib/action_dispatch/http/response.rb

@@ -2,6 +2,7 @@
 require 'active_support/core_ext/module/delegation'
 require 'active_support/core_ext/object/blank'
 require 'active_support/core_ext/class/attribute_accessors'
+require 'monitor'
 
 module ActionDispatch # :nodoc:
   # Represents an HTTP response generated by a controller action. Use it to
@@ -62,12 +63,17 @@ class Response
 
     include Rack::Response::Helpers
     include ActionDispatch::Http::Cache::Response
+    include MonitorMixin
 
     def initialize(status = 200, header = {}, body = [])
+      super()
+
       self.body, self.header, self.status = body, header, status
 
       @sending_file = false
-      @blank = false
+      @blank        = false
+      @cv           = new_cond
+      @committed    = false
 
       if content_type = self[CONTENT_TYPE]
         type, charset = content_type.split(/;\s*charset=/)
@@ -80,6 +86,23 @@ def initialize(status = 200, header = {}, body = [])
       yield self if block_given?
     end
 
+    def await_commit
+      synchronize do
+        @cv.wait_until { @committed }
+      end
+    end
+
+    def commit!
+      synchronize do
+        @committed = true
+        @cv.broadcast
+      end
+    end
+
+    def committed?
+      synchronize { @committed }
+    end
+
     def status=(status)
       @status = Rack::Utils.status_code(status)
     end

actionpack/test/dispatch/response_test.rb

@@ -5,6 +5,15 @@ def setup
     @response = ActionDispatch::Response.new
   end
 
+  def test_can_wait_until_commit
+    t = Thread.new {
+      assert @response.await_commit
+    }
+    @response.commit!
+    assert @response.committed?
+    t.join
+  end
+
   def test_response_body_encoding
     body = ["hello".encode('utf-8')]
     response = ActionDispatch::Response.new 200, {}, body