void closeAll() {
      // use a copy of the connections to be absolutely sure the concurrent
      // iterator doesn't miss a connection
      for (SimpleServerRpcConnection connection : toArray()) {
        close(connection);
      }
    }
The number of open RPC conections
@return the number of open rpc connections
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/SimpleRpcServer.java