Fully initialize routes before the first request is handled

`AD::Journey::GTG::Simulator` is lazily built the first time
`Journey::Router#find_routes` is invoked, which happens when
the first request is served.

On large applications with many routes, building the simulator
can take several hundred milliseconds (~700ms for us).

Triggering this initialization during the boot process reduces
the impact of deploys on the application response time.

2 files changed, 17 insertions, 1 deletions

diff --git a/railties/lib/rails/application/finisher.rb b/railties/lib/rails/application/finisher.rb
index a855e8fab0..c027d06663 100644
--- a/railties/lib/rails/application/finisher.rb
+++ b/railties/lib/rails/application/finisher.rb
@@ -124,6 +124,7 @@ module Rails
       # the hook are taken into account.
       initializer :set_routes_reloader_hook do |app|
         reloader = routes_reloader
+        reloader.eager_load = app.config.eager_load
         reloader.execute_if_updated
         reloaders << reloader
         app.reloader.to_run do
diff --git a/railties/lib/rails/application/routes_reloader.rb b/railties/lib/rails/application/routes_reloader.rb
index cf0a4e128f..e02ef629f2 100644
--- a/railties/lib/rails/application/routes_reloader.rb
+++ b/railties/lib/rails/application/routes_reloader.rb
@@ -4,11 +4,13 @@ module Rails
   class Application
     class RoutesReloader
       attr_reader :route_sets, :paths
-      delegate :execute_if_updated, :execute, :updated?, to: :updater
+      attr_accessor :eager_load
+      delegate :updated?, to: :updater
 
       def initialize
         @paths      = []
         @route_sets = []
+        @eager_load = false
       end
 
       def reload!
@@ -19,6 +21,19 @@ module Rails
         revert
       end
 
+      def execute
+        ret = updater.execute
+        route_sets.each(&:eager_load!) if eager_load
+        ret
+      end
+
+      def execute_if_updated
+        if updated = updater.execute_if_updated
+          route_sets.each(&:eager_load!) if eager_load
+        end
+        updated
+      end
+
     private
 
       def updater