Add the ability to perform background migrations

Background migrations can be used to perform long running data
migrations without these blocking a deployment procedure.

See MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11854 for
more information.

1 files changed, 31 insertions, 0 deletions

diff --git a/lib/gitlab/background_migration.rb b/lib/gitlab/background_migration.rb
new file mode 100644
index 00000000000..914a3b72abd
--- /dev/null
+++ b/lib/gitlab/background_migration.rb
@@ -0,0 +1,31 @@
+module Gitlab
+  module BackgroundMigration
+    # Begins stealing jobs from the background migrations queue, blocking the
+    # caller until all jobs have been completed.
+    #
+    # steal_class - The name of the class for which to steal jobs.
+    def self.steal(steal_class)
+      queue = Sidekiq::Queue.
+        new(BackgroundMigrationWorker.sidekiq_options['queue'])
+
+      queue.each do |job|
+        migration_class, migration_args = job.args
+
+        next unless migration_class == steal_class
+
+        perform(migration_class, migration_args)
+
+        job.delete
+      end
+    end
+
+    # class_name - The name of the background migration class as defined in the
+    #              Gitlab::BackgroundMigration namespace.
+    #
+    # arguments - The arguments to pass to the background migration's "perform"
+    #             method.
+    def self.perform(class_name, arguments)
+      const_get(class_name).new.perform(*arguments)
+    end
+  end
+end