schoefmax / klarlack

now we use this in lib/ext/klarlack_hack.rb (only works for non-threading rails...), only the thread will hang, which is not as bad as whole rails hanging...

# @conn.write can freeze if varnish restarts
# Timeout does not help...
# so we do it asynchronous (Thread creation takes ~ 40ms)
Varnish::Client # require it ...
module Varnish::Client
  def cmd(name, *params)
    Thread.new do
      begin
        @conn.write "#{name} #{params.join(' ').gsub('\\', '\\\\\\')}\n"
        status, length = @conn.gets.split # <status> <content_length>\n
        content = @conn.read(length.to_i + 1) # +1 = \n
        content.chomp!
        raise Error, "Command #{name} returned with status #{status}: #{content}" if status.to_i != 200
          rescue Exception => e
        HoptoadNotifier.notify(e)
      end
    end
  end
end

Happy New Year and sorry for the delay.

Looks like a timeout issue to me (I assume you are using timeouts with SystemTimer?)
I'll try to reproduce it. Maybe updating the socket code helps - the timeout stuff comes from memcache-client which has since improved it's own code futher.
sigh - we could really need a proper socket lib that handles timeouts correctly...