cpp: TNonBlockingServer: Use separate monitor for max queue

We were using the same monitor for max queue size and empty queue, this
meant the notifies might be going to the wrong place.

This change significantly reduces the time spent in futex calls in
loaded servers.

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@920667 13f79535-47bb-0310-9956-ffa450edef68
1 file changed