install sidekiq

Gemfile

@@ -21,6 +21,7 @@ gem 'devise'
 gem 'carrierwave'
 gem 'kaminari'
 gem "settingslogic"
+gem 'sidekiq'
 
 group :development, :test do
   # Call 'byebug' anywhere in the code to stop execution and get a debugger console
@@ -30,10 +31,8 @@ end
 group :development do
   # Access an IRB console on exception pages or by using <%= console %> anywhere in the code.
   gem 'web-console', '>= 3.3.0'
-  gem 'listen', '>= 3.0.5', '< 3.2'
   # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
   gem 'spring'
-  gem 'spring-watcher-listen', '~> 2.0.0'
 end
 
 # Windows does not include zoneinfo files, so bundle the tzinfo-data gem

Gemfile.lock

@@ -48,6 +48,7 @@ GEM
       activesupport (>= 4.0.0)
       mime-types (>= 1.16)
     concurrent-ruby (1.0.5)
+    connection_pool (2.2.1)
     crass (1.0.2)
     devise (4.3.0)
       bcrypt (~> 3.0)
@@ -75,10 +76,6 @@ GEM
       activerecord
       kaminari-core (= 1.0.1)
     kaminari-core (1.0.1)
-    listen (3.1.5)
-      rb-fsevent (~> 0.9, >= 0.9.4)
-      rb-inotify (~> 0.9, >= 0.9.7)
-      ruby_dep (~> 1.2)
     loofah (2.1.1)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
@@ -97,6 +94,8 @@ GEM
     orm_adapter (0.5.0)
     puma (3.10.0)
     rack (2.0.3)
+    rack-protection (2.0.0)
+      rack
     rack-test (0.7.0)
       rack (>= 1.0, < 3)
     rails (5.1.4)
@@ -126,10 +125,10 @@ GEM
     rb-fsevent (0.10.2)
     rb-inotify (0.9.10)
       ffi (>= 0.5.0, < 2)
+    redis (4.0.1)
     responders (2.4.0)
       actionpack (>= 4.2.0, < 5.3)
       railties (>= 4.2.0, < 5.3)
-    ruby_dep (1.5.0)
     sass (3.5.1)
       sass-listen (~> 4.0.0)
     sass-listen (4.0.0)
@@ -142,11 +141,13 @@ GEM
       sprockets-rails (>= 2.0, < 4.0)
       tilt (>= 1.1, < 3)
     settingslogic (2.0.9)
+    sidekiq (5.0.5)
+      concurrent-ruby (~> 1.0)
+      connection_pool (~> 2.2, >= 2.2.0)
+      rack-protection (>= 1.5.0)
+      redis (>= 3.3.4, < 5)
     spring (2.0.2)
       activesupport (>= 4.2)
-    spring-watcher-listen (2.0.1)
-      listen (>= 2.7, < 4.0)
-      spring (>= 1.2, < 3.0)
     sprockets (3.7.1)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
@@ -181,14 +182,13 @@ DEPENDENCIES
   devise
   figaro
   kaminari
-  listen (>= 3.0.5, < 3.2)
   mysql2 (>= 0.3.18, < 0.5)
   puma (~> 3.7)
   rails (~> 5.1.4)
   sass-rails (~> 5.0)
   settingslogic
+  sidekiq
   spring
-  spring-watcher-listen (~> 2.0.0)
   tzinfo-data
   uglifier (>= 1.3.0)
   web-console (>= 3.3.0)

app/controllers/applies_controller.rb

@@ -40,7 +40,7 @@ class AppliesController < ApplicationController
                                 cv:      session[:candidate_cv])
     if @application.save
       flash[:notice] = 'Congratulation! Job was successfully applied'
-      ApplyJobMailer.successful_email(@application).deliver
+      EmailWorker.perform_in(1.seconds, @application.id)
       clear_session
     end
   end

app/workers/email_worker.rb

+class EmailWorker
+  include Sidekiq::Worker
+
+  def perform(application_id)
+    application = ApplyJob.find(application_id)
+    ApplyJobMailer.successful_email(application).deliver
+  end
+end

config/environments/development.rb

@@ -48,9 +48,9 @@ Rails.application.configure do
   # Raises error for missing translations
   # config.action_view.raise_on_missing_translations = true
 
-  # Use an evented file watcher to asynchronously detect changes in source code,
-  # routes, locales, etc. This feature depends on the listen gem.
-  config.file_watcher = ActiveSupport::EventedFileUpdateChecker
+  # config.action_mailer.delivery_method = :smtp
+  # config.action_mailer.smtp_settings = { address: 'localhost',
+  #                                        port: 1025 }
   config.action_mailer.smtp_settings = {
   address: "smtp.gmail.com",
   port: 587,

config/routes.rb

 Rails.application.routes.draw do
+  require 'sidekiq/web'
   root 'jobs#index'
   devise_for :users
 
@@ -14,4 +15,5 @@ Rails.application.routes.draw do
   get 'apply' => "applies#apply"
   post 'confirm' => "applies#confirm"
   post 'done' => "applies#done"
+  mount Sidekiq::Web, at: '/sidekiq'
 end