Integrating 0mq w/ EventMachine into a rails application

*scratch*

* Rack
  - Rack::FiberPool provides a Fiber for each request

* Application Server
  - Thin: starts its own EM reactor
  - Passenger: Start a new reactor in a new thread
  - Other: Start a new reactor in a new thread

* Rails
  - initialzier: Start a new EM reactor (depending on app server)

* Code
  - questions:
    - At this point, how do we use the existing EM reactor? There is
      already a thread with an EM reactor loop running.
  - Every app process needs a EM thread. The EM thread is an event loop.
  - When code makes an blocking call it falls back to the event
    loop and lets another Fiber resume.
    - That shits gonna block *within* the Fiber-wrapped rails request
  - em-zeromq manipulates the file descriptor associated with the socket
  - 0mq does it magic
  - em-zeromq watches fd associated with the socket. When there is
    activity it is reported back to em-zeromq (how?)

* Goal
  - Make a 0mq request and wait for a response with an rails request

* Test
  - Use thin + Rack/Fiber-Pool + EM-ZMQ
    - Push & Subscribe with 0mq
      - Push should not block
      - Subscribe should block until a message is received