title: Rails: Sidekiq Workers must be thread-safe. What Does it mean?
body: <p>I read this about Sidekiq:</p>
  
  <p>Sidekiq is multithreaded so your Workers must be thread-safe.</p>
  
  <p>What does it mean? What is 'thread-safe' code? Can someone make example about that? Thank you very much.</p>