Merge branch 'master' into ide

* master: (86 commits)
  Show all labels
  33874 confidential issue redesign
  Exclude merge_jid on Import/Export attribute configuration
  Resolve "User dropdown in filtered search does not load avatar on `master`"
  Re-add column locked_at on migration rollback
  Group-level new issue & MR using previously selected project
  [EE Backport] Update log audit event in omniauth_callbacks_controller.rb
  more eagerly bail when the state is prevented
  Move locked_at removal to post-deployment migration
  Add class to other sidebars
  Improve mobile sidebar
  reduce iterations by keeping a count of remaining enablers
  Store & use ConvDev percentages returned by Version app
  Store MergeWorker JID on merge request, and clean up stuck merges
  Backport changes in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2551 to CE
  DRY up caching in AbstractReferenceFilter
  Update CHANGELOG
  Add CHANGELOG entry
  Fix html structure Removes test for removed behavior
  Port form back to use form_tag
  ...

1 files changed, 62 insertions, 0 deletions

diff --git a/lib/gitlab/daemon.rb b/lib/gitlab/daemon.rb
new file mode 100644
index 00000000000..dfd17e35707
--- /dev/null
+++ b/lib/gitlab/daemon.rb
@@ -0,0 +1,62 @@
+module Gitlab
+  class Daemon
+    def self.initialize_instance(*args)
+      raise "#{name} singleton instance already initialized" if @instance
+      @instance = new(*args)
+      Kernel.at_exit(&@instance.method(:stop))
+      @instance
+    end
+
+    def self.instance
+      @instance ||= initialize_instance
+    end
+
+    attr_reader :thread
+
+    def thread?
+      !thread.nil?
+    end
+
+    def initialize
+      @mutex = Mutex.new
+    end
+
+    def enabled?
+      true
+    end
+
+    def start
+      return unless enabled?
+
+      @mutex.synchronize do
+        return thread if thread?
+
+        @thread = Thread.new { start_working }
+      end
+    end
+
+    def stop
+      @mutex.synchronize do
+        return unless thread?
+
+        stop_working
+
+        if thread
+          thread.wakeup if thread.alive?
+          thread.join
+          @thread = nil
+        end
+      end
+    end
+
+    private
+
+    def start_working
+      raise NotImplementedError
+    end
+
+    def stop_working
+      # no-ops
+    end
+  end
+end