Mirror services execution is now threaded (with promises)

Author: SGospodinov

lib/active_storage/service/mirror_service.rb

@@ -1,4 +1,5 @@
 require "active_support/core_ext/module/delegation"
+require "concurrent"
 
 class ActiveStorage::Service::MirrorService < ActiveStorage::Service
   attr_reader :services
@@ -26,9 +27,9 @@ def primary_service
     end
 
     def perform_across_services(method, *args)
-      # FIXME: Convert to be threaded
-      services.collect do |service|
-        service.public_send method, *args
+      promises = services.collect do |service|
+        Concurrent::Promise.execute { service.public_send method, *args }
       end
+      Concurrent::Promise.zip(*promises).value
     end
 end