1 files changed, 19 insertions, 3 deletions
diff --git a/app/services/merge_requests/merge_service.rb b/app/services/merge_requests/merge_service.rb
index 27f474b0fe7..5e7eee4f1c3 100644
--- a/app/services/merge_requests/merge_service.rb
+++ b/app/services/merge_requests/merge_service.rb
@@ -8,16 +8,22 @@ module MergeRequests
   # Executed when you do merge via GitLab UI
   #
   class MergeService < MergeRequests::MergeBaseService
+    include Gitlab::Utils::StrongMemoize
+
     GENERIC_ERROR_MESSAGE = 'An error occurred while merging'
+    LEASE_TIMEOUT = 15.minutes.to_i
 
     delegate :merge_jid, :state, to: :@merge_request
 
     def execute(merge_request, options = {})
       if project.merge_requests_ff_only_enabled && !self.is_a?(FfMergeService)
-        FfMergeService.new(project, current_user, params).execute(merge_request)
+        FfMergeService.new(project: project, current_user: current_user, params: params).execute(merge_request)
         return
       end
 
+      return if merge_request.merged?
+      return unless exclusive_lease(merge_request.id).try_obtain
+
       @merge_request = merge_request
       @options = options
 
@@ -34,6 +40,8 @@ module MergeRequests
       log_info("Merge process finished on JID #{merge_jid} with state #{state}")
     rescue MergeError => e
       handle_merge_error(log_message: e.message, save_message_on_model: true)
+    ensure
+      exclusive_lease(merge_request.id).cancel
     end
 
     private
@@ -96,14 +104,14 @@ module MergeRequests
     rescue Gitlab::Git::PreReceiveError => e
       raise MergeError,
             "Something went wrong during merge pre-receive hook. #{e.message}".strip
-    rescue => e
+    rescue StandardError => e
       handle_merge_error(log_message: e.message)
       raise_error(GENERIC_ERROR_MESSAGE)
     end
 
     def after_merge
       log_info("Post merge started on JID #{merge_jid} with state #{state}")
-      MergeRequests::PostMergeService.new(project, current_user).execute(merge_request)
+      MergeRequests::PostMergeService.new(project: project, current_user: current_user).execute(merge_request)
       log_info("Post merge finished on JID #{merge_jid} with state #{state}")
 
       if delete_source_branch?
@@ -146,5 +154,13 @@ module MergeRequests
       # loaded from the database they're strings
       params.with_indifferent_access[:sha] == merge_request.diff_head_sha
     end
+
+    def exclusive_lease(merge_request_id)
+      strong_memoize(:"exclusive_lease_#{merge_request_id}") do
+        lease_key = ['merge_requests_merge_service', merge_request_id].join(':')
+
+        Gitlab::ExclusiveLease.new(lease_key, timeout: LEASE_TIMEOUT)
+      end
+    end
   end
 end