1 files changed, 17 insertions, 6 deletions
diff --git a/app/services/ci/register_build_service.rb b/app/services/ci/register_build_service.rb
index 4ff268a6f06..f0ed09a629a 100644
--- a/app/services/ci/register_build_service.rb
+++ b/app/services/ci/register_build_service.rb
@@ -7,15 +7,19 @@ module Ci
 
       builds =
         if current_runner.shared?
-          # don't run projects which have not enables shared runners
-          builds.joins(:project).where(projects: { builds_enabled: true, shared_runners_enabled: true })
+          builds.
+            # don't run projects which have not enabled shared runners
+            joins(:project).where(projects: { builds_enabled: true, shared_runners_enabled: true }).
+
+            # this returns builds that are ordered by number of running builds
+            # we prefer projects that don't use shared runners at all
+            joins("LEFT JOIN (#{running_builds_for_shared_runners.to_sql}) AS project_builds ON ci_builds.gl_project_id=project_builds.gl_project_id").
+            order('COALESCE(project_builds.running_builds, 0) ASC', 'ci_builds.id ASC')
         else
-          # do run projects which are only assigned to this runner
-          builds.where(project: current_runner.projects.where(builds_enabled: true))
+          # do run projects which are only assigned to this runner (FIFO)
+          builds.where(project: current_runner.projects.where(builds_enabled: true)).order('created_at ASC')
         end
 
-      builds = builds.order('created_at ASC')
-
       build = builds.find do |build|
         build.can_be_served?(current_runner)
       end
@@ -35,5 +39,12 @@ module Ci
     rescue StateMachines::InvalidTransition
       nil
     end
+
+    private
+
+    def running_builds_for_shared_runners
+      Ci::Build.running.where(runner: Ci::Runner.shared).
+        group(:gl_project_id).select(:gl_project_id, 'count(*) AS running_builds')
+    end
   end
 end