Merge branch 'feature/improve-async-pipeline-processing' into 'master'

Improve asynchronous pipeline processing

## What does this MR do?

This MR improves asynchronous processing of pipeline.

## Why was this MR needed?

It eliminates some race conditions and improves performance.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing

## What are the relevant issue / merge request numbers?

Related merge request:  !6410  
Extracted from !6411

See merge request !6650

1 files changed, 11 insertions, 6 deletions

diff --git a/app/models/commit_status.rb b/app/models/commit_status.rb
index ee3396abe04..9fa8d17e74e 100644
--- a/app/models/commit_status.rb
+++ b/app/models/commit_status.rb
@@ -84,13 +84,18 @@ class CommitStatus < ActiveRecord::Base
       commit_status.update_attributes finished_at: Time.now
     end
 
-    after_transition any => [:success, :failed, :canceled] do |commit_status|
-      commit_status.pipeline.try(:process!)
-      true
-    end
-
     after_transition do |commit_status, transition|
-      commit_status.pipeline.try(:build_updated) unless transition.loopback?
+      commit_status.pipeline.try do |pipeline|
+        break if transition.loopback?
+
+        if commit_status.complete?
+          ProcessPipelineWorker.perform_async(pipeline.id)
+        end
+
+        UpdatePipelineWorker.perform_async(pipeline.id)
+      end
+
+      true
     end
 
     after_transition [:created, :pending, :running] => :success do |commit_status|