Why is the error `Celluloid::Condition signaled spuriously` caused in Celluloid?

I'm trying to wait on a condition of an async code, here's the snippet:

condition = Celluloid::Condition.new   
Rails.logger.debug "Sending RPC request to #{subject}"
NATS.start uri: ENV['NATS_SERVER'] do 
  Rails.logger.debug "Connected to #{ENV['NATS_SERVER']}"
  sid = NATS.request(subject,msg) do |response|
    Rails.logger.debug "Assigning response"
    condition.signal response
    NATS.stop
  end
  NATS.timeout(sid, 1) do
    NATS.stop
    condition.signal ASYNC_ERROR
    raise "One second timeout waiting for a NATS RPC reply from #{subject}"
  end
end

result = condition.wait
if result = ASYNC_ERROR
  raise "Error in RPC call"
else
  return result
end

I get the exception Celluloid::Condition signaled spuriously but there's no extra information and I don't really understand why is it caused and https://github.com/celluloid/celluloid/wiki/Conditions doesn't provide more information.

Why is this caused and how can I fix it?

And to answer your question exactly like your stated question, using a condition.

Within the scope of an actor:

class Nats
  include Celluloid

  def initialize
    @condition = Celluloid::Condition.new
  end

  def start
    Rails.logger.debug "Sending RPC request to #{subject}"
    NATS.start uri: ENV['NATS_SERVER'] do 
      Rails.logger.debug "Connected to #{ENV['NATS_SERVER']}"
      sid = NATS.request(subject,msg) do |response|
        Rails.logger.debug "Assigning response"
        @condition.signal response
        NATS.stop
      end
      NATS.timeout(sid, 1) do
        NATS.stop
        @condition.signal ASYNC_ERROR
        raise "One second timeout waiting for a NATS RPC reply from #{subject}"
      end
    end
  end

  def value
    @condition.wait
  end
end

nats = Nats.new
nats.async.start

result = nats.value
if result = ASYNC_ERROR
  raise "Error in RPC call"
else
  return result
end

This is even less tested, but ought to show you the basic approach if you aren't going to use a Future like my other answer.