From 71ea4ad7fca483e2f5ddc7fff0ad97120074be4c Mon Sep 17 00:00:00 2001
From: Sam Saffron <sam.saffron@gmail.com>
Date: Sun, 6 Oct 2019 23:57:03 -0400
Subject: [PATCH] PERF: reuse renderer when rendering email templates

Previous to this fix we were leaking methods on the internal action view
template class per render.

This caused email generation to be very low and a steady memory leak in the
application in sidekiq when sending out emails

The behavior change is new to Rails 6 so this fix does not need to be
backported into stable.
---
 app/mailers/user_notifications.rb          | 2 +-
 app/services/user_notification_renderer.rb | 6 ++++++
 lib/email/message_builder.rb               | 4 +---
 lib/email/renderer.rb                      | 4 +---
 4 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/app/mailers/user_notifications.rb b/app/mailers/user_notifications.rb
index ee5a516a734..de8ac561eb9 100644
--- a/app/mailers/user_notifications.rb
+++ b/app/mailers/user_notifications.rb
@@ -589,7 +589,7 @@ class UserNotifications < ActionMailer::Base
       end
 
       unless translation_override_exists
-        html = UserNotificationRenderer.with_view_paths(Rails.configuration.paths["app/views"]).render(
+        html = UserNotificationRenderer.instance.render(
           template: 'email/notification',
           format: :html,
           locals: { context_posts: context_posts,
diff --git a/app/services/user_notification_renderer.rb b/app/services/user_notification_renderer.rb
index 8ad7d209145..edf11712838 100644
--- a/app/services/user_notification_renderer.rb
+++ b/app/services/user_notification_renderer.rb
@@ -4,4 +4,10 @@ class UserNotificationRenderer < ActionView::Base
   include ApplicationHelper
   include UserNotificationsHelper
   include EmailHelper
+
+  def self.instance
+    @instance ||= UserNotificationRenderer.with_view_paths(
+      Rails.configuration.paths["app/views"]
+    )
+  end
 end
diff --git a/lib/email/message_builder.rb b/lib/email/message_builder.rb
index d1e83b03e01..654c4ae3c67 100644
--- a/lib/email/message_builder.rb
+++ b/lib/email/message_builder.rb
@@ -94,9 +94,7 @@ module Email
         html_override.gsub!("%{respond_instructions}", "")
       end
 
-      html = UserNotificationRenderer.with_view_paths(
-        Rails.configuration.paths["app/views"]
-      ).render(
+      html = UserNotificationRenderer.instance.render(
         template: 'layouts/email_template',
         format: :html,
         locals: { html_body: html_override.html_safe }
diff --git a/lib/email/renderer.rb b/lib/email/renderer.rb
index 641fb207bed..2f9203bd6c3 100644
--- a/lib/email/renderer.rb
+++ b/lib/email/renderer.rb
@@ -18,9 +18,7 @@ module Email
       style = if @message.html_part
         Email::Styles.new(@message.html_part.body.to_s, @opts)
       else
-        unstyled = UserNotificationRenderer.with_view_paths(
-          Rails.configuration.paths["app/views"]
-        ).render(
+        unstyled = UserNotificationRenderer.instance.render(
           template: 'layouts/email_template',
           format: :html,
           locals: { html_body: PrettyText.cook(text).html_safe }