Merge branch 'note-background-job' into 'master'

Background process note logic for #3948

Quick and dirty way to get *most* of the note processing out of band and into the background. Seeing some pretty nice speed bumps. Keep in mind that doing this in process results in slower and slower responses as more notes are added and more participants exist.

```
without background processing
  Completed 200 OK in 627ms (Views: 0.5ms | ActiveRecord: 32.3ms)
  Completed 200 OK in 478ms (Views: 0.8ms | ActiveRecord: 28.3ms)
  Completed 200 OK in 1107ms (Views: 0.6ms | ActiveRecord: 36.6ms)

with background processing
  Completed 200 OK in 108ms (Views: 0.6ms | ActiveRecord: 4.7ms)
  Completed 200 OK in 78ms (Views: 0.5ms | ActiveRecord: 4.5ms)
  Completed 200 OK in 164ms (Views: 0.5ms | ActiveRecord: 8.3ms)
```

As you can see, speeds are consistent when doing the harder work out of process. I'm not sure the number of sql queries we're saving, but based on the logs alone it's a pretty good amount.

@dzaporozhets @yorickpeterse I would love some input on this.

See merge request !2631

4 files changed, 45 insertions, 18 deletions

diff --git a/app/controllers/projects/notes_controller.rb b/app/controllers/projects/notes_controller.rb
index 4a2599dda37..1b9dd568043 100644
--- a/app/controllers/projects/notes_controller.rb
+++ b/app/controllers/projects/notes_controller.rb
@@ -106,7 +106,7 @@ class Projects::NotesController < Projects::ApplicationController
           { notes_left: [note], notes_right: [] }
         else
           { notes_left: [], notes_right: [note] }
-       end
+        end
     else
       template = "projects/notes/_diff_notes_with_reply"
       locals = { notes: [note] }
diff --git a/app/services/notes/create_service.rb b/app/services/notes/create_service.rb
index a8486e6a5a1..8d9661167b5 100644
--- a/app/services/notes/create_service.rb
+++ b/app/services/notes/create_service.rb
@@ -6,27 +6,12 @@ module Notes
       note.system = false
 
       if note.save
-        notification_service.new_note(note)
-
-        # Skip system notes, like status changes and cross-references and awards
-        unless note.system || note.is_award
-          event_service.leave_note(note, note.author)
-          note.create_cross_references!
-          execute_hooks(note)
-        end
+        # Finish the harder work in the background
+        NewNoteWorker.perform_in(2.seconds, note.id, params)
       end
 
       note
     end
 
-    def hook_data(note)
-      Gitlab::NoteDataBuilder.build(note, current_user)
-    end
-
-    def execute_hooks(note)
-      note_data = hook_data(note)
-      note.project.execute_hooks(note_data, :note_hooks)
-      note.project.execute_services(note_data, :note_hooks)
-    end
   end
 end
diff --git a/app/services/notes/post_process_service.rb b/app/services/notes/post_process_service.rb
new file mode 100644
index 00000000000..f37d3c50cdd
--- /dev/null
+++ b/app/services/notes/post_process_service.rb
@@ -0,0 +1,30 @@
+module Notes
+  class PostProcessService
+
+    attr_accessor :note
+
+    def initialize(note)
+      @note = note
+    end
+
+    def execute
+      # Skip system notes, like status changes and cross-references and awards
+      unless @note.system || @note.is_award
+        EventCreateService.new.leave_note(@note, @note.author)
+        @note.create_cross_references!
+        execute_note_hooks
+      end
+    end
+
+    def hook_data
+      Gitlab::NoteDataBuilder.build(@note, @note.author)
+    end
+
+    def execute_note_hooks
+      note_data = hook_data
+      @note.project.execute_hooks(note_data, :note_hooks)
+      @note.project.execute_services(note_data, :note_hooks)
+    end
+
+  end
+end
diff --git a/app/workers/new_note_worker.rb b/app/workers/new_note_worker.rb
new file mode 100644
index 00000000000..1b3232cd365
--- /dev/null
+++ b/app/workers/new_note_worker.rb
@@ -0,0 +1,12 @@
+class NewNoteWorker
+  include Sidekiq::Worker
+
+  sidekiq_options queue: :default
+
+  def perform(note_id, note_params)
+    note = Note.find(note_id)
+
+    NotificationService.new.new_note(note)
+    Notes::PostProcessService.new(note).execute
+  end
+end