title: Do singleton classes create problems in a multi-threaded app?
body: <p>This might be premature optimization, or premature over-cautionization, but I'm avoiding using singletons on a few classes because I'm concerned that down the road I'll need to run my app as multi-threaded, and that the singletons will create conflicts and messiness.  Do singletons have this issue in Ruby, or is there some kind of built in namespace so that when an a class refers to the singleton, only the singleton on the same thread is returned?</p>
  
  <p>Edit: to clarify these are observable classes which when updated cause the other classes that are watching them to update.  I'm not sure if this is thread safe or not, but I do know that right now I'm passing these observable classes around a ton and it's kind of annoying.  And they do seem like natural singleton classes.</p>