knight:
If you were using my code, there was a sided error in the code that is now corrected in the wiki, however, that error seems unrelated. To be honest, if I am reading your code correctly, you have only registered the channel on the server, which just wont work as the client has no channel to receive on...
libarclite:
If in doubt you could register multiple channels per thread (instead of auto registering during the init phase, just create another with a different name). However, both attr() and writeAndFlush() are netty methods and netty at its core is both asynchronous and thread safe so I assume it should be fine! According to the JD: http://netty.io/4.0/api/io/netty/util/Attribute.html Attributes can be updated automatically so are thread safe.