boolean close(SimpleServerRpcConnection connection) {
      boolean exists = remove(connection);
      if (exists) {
        if (LOG.isTraceEnabled()) {
          LOG.trace(Thread.currentThread().getName() + ": disconnecting client " + connection
            + ". Number of active connections: " + size());
        }
        // only close if actually removed to avoid double-closing due
        // to possible races
        connection.close();
      }
      return exists;
    }
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