2 files changed, 23 insertions, 2 deletions
diff --git a/actionpack/lib/action_controller/metal/live.rb b/actionpack/lib/action_controller/metal/live.rb
index e3c540bf5f..acc4507b2d 100644
--- a/actionpack/lib/action_controller/metal/live.rb
+++ b/actionpack/lib/action_controller/metal/live.rb
@@ -237,9 +237,8 @@ module ActionController
       # 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 {
+      new_controller_thread {
         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. :'(
@@ -270,6 +269,18 @@ module ActionController
       raise error if error
     end
 
+    # Spawn a new thread to serve up the controller in.  This is to get
+    # around the fact that Rack isn't based around IOs and we need to use
+    # a thread to stream data from the response bodies.  Nobody should call
+    # this method except in Rails internals. Seriously!
+    def new_controller_thread # :nodoc:
+      Thread.new {
+        t2 = Thread.current
+        t2.abort_on_exception = true
+        yield
+      }
+    end
+
     def log_error(exception)
       logger = ActionController::Base.logger
       return unless logger
diff --git a/actionpack/lib/action_controller/test_case.rb b/actionpack/lib/action_controller/test_case.rb
index b43bb9dc17..ac45b2e363 100644
--- a/actionpack/lib/action_controller/test_case.rb
+++ b/actionpack/lib/action_controller/test_case.rb
@@ -12,6 +12,16 @@ module ActionController
     include Testing::Functional
   end
 
+  module Live
+    # Disable controller / rendering threads in tests.  User tests can access
+    # the database on the main thread, so they could open a txn, then the
+    # controller thread will open a new connection and try to access data
+    # that's only visible to the main thread's txn.  This is the problem in #23483
+    def new_controller_thread # :nodoc:
+      yield
+    end
+  end
+
   # ActionController::TestCase will be deprecated and moved to a gem in Rails 5.1.
   # Please use ActionDispatch::IntegrationTest going forward.
   class TestRequest < ActionDispatch::TestRequest #:nodoc: