Sucker Punch Async Fails When Using Shotgun

README.md

Start the server

bundle exec shotgun

Make a request

curl 'http://localhost:9393/log'
curl 'http://localhost:9393/async-log'

app.rb

class LogJob
  include SuckerPunch::Job
  workers 4

  def perform(event)
    File.open("log.#{rand(10_000)}.txt", 'a') { |f| f.puts event }
    File.open('log.txt', 'a') { |f| f.puts event }

    true
  end
end

class MyApp < Sinatra::Base
  get '/log' do
    LogJob.new.perform(type: 'log', value: 'regular')
  end

  get '/async-log' do
    LogJob.new.async.perform(type: 'log', value: 'async')
  end
end

config.ru

require 'bundler'
Bundler.require
require 'sucker_punch'
require 'sinatra'

require './app.rb'
run MyApp

Gemfile

source 'https://rubygems.org'

gem 'sucker_punch', '~> 1.5.0'
gem 'sinatra', '~> 1.4.6'
gem 'shotgun'