Sustained queuing on one listener can block requests from other listeners

[Stan Hu <stanhu@gmail.com>]

My unicorn.rb has two listeners:

listen "127.0.0.1:8080", :tcp_nopush => false
listen "/var/run/unicorn.socket", :backlog => 1024

We found that because of the greedy attempt to accept new connections
before calling select() in
https://github.com/defunkt/unicorn/blob/981f561a726bb4307d01e4a09a308edba8d69fe3/lib/unicorn/http_server.rb#L707-L714,
listeners on another socket stall out until the first listener is
drained. We would expect Unicorn to round-robin between the two
listeners, but that doesn't happen as long as there is work to be done
for the first listener. We've verified that deleting that `redo` block
fixes the problem.

What do you think about the various options?

1. Only running that redo block if there is one listener
2. Removing the redo block entirely