I spent this past weekend adding eventmachine support for the Cassandra gem. We’re using Cassandra at OneSpot as our next-gen data store and need EM support. They were nice enough to pull my changes yesterday so the next release of the thrift_client and cassandra gems should work in EM. You just need to do this:

require 'thrift_client/event_machine'
    EM.run do
      Fiber.new do
        @twitter = Cassandra.new('Twitter', "127.0.0.1:9160", :transport => Thrift::EventMachineTransport, :transport_wrapper => nil)
        @twitter.clear_keyspace!
        EM.stop
      end.resume
    end

The key is the :transport and :transport_wrapper options which override the default, Socket-based implementation. Like all of my EventMachine code, this requires Ruby 1.9.