em-test.rb

require "em-synchrony"
require "redis/connection/synchrony"
require "redis"

class RequestHandler < EM::P::HeaderAndContentProtocol
  attr_accessor :redis

  def receive_request(http_headers, http_content)

    puts redis.class
    # ^^^ this line prints "Redis"

    puts redis.smembers 'queues'
    # ^^^ this line raises lib/em-synchrony.rb:75:in `yield': can't yield from root fiber (FiberError)

  end

end


EM.epoll

EM.synchrony do

  redis = Redis.new(path: "/tmp/redis.sock")

  EM.start_server("/tmp/server.sock", RequestHandler) do |handler|
    handler.redis = redis
  end

end

exception-stack-trace.txt

Redis
/tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis/connection/synchrony.rb:81:in `yield': can't yield from root fiber (FiberError)
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis/connection/synchrony.rb:81:in `connect'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis/client.rb:271:in `establish_connection'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis/client.rb:69:in `connect'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis/client.rb:290:in `ensure_connected'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis/client.rb:177:in `block in process'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis/client.rb:256:in `logging'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis/client.rb:176:in `process'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis/client.rb:84:in `call'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis.rb:1247:in `block in smembers'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis.rb:36:in `block in synchronize'
        from /usr/local/rvm/rubies/ruby-2.0.0-p0/lib/ruby/2.0.0/monitor.rb:211:in `mon_synchronize'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis.rb:36:in `synchronize'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/redis-3.0.4/lib/redis.rb:1246:in `smembers'
        from em-test.rb:13:in `receive_request'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/eventmachine-1.0.3/lib/em/protocols/header_and_content.rb:99:in `dispatch_request'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/eventmachine-1.0.3/lib/em/protocols/header_and_content.rb:73:in `receive_line'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/eventmachine-1.0.3/lib/em/protocols/linetext2.rb:64:in `receive_data'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/eventmachine-1.0.3/lib/eventmachine.rb:187:in `run_machine'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/eventmachine-1.0.3/lib/eventmachine.rb:187:in `run'
        from /tmp/em-test/bundle/ruby/2.0.0/gems/em-synchrony-1.0.3/lib/em-synchrony.rb:38:in `synchrony'
        from em-test.rb:23:in `<main>'