@Override
  public void cleanupConnection() {
    execute(eventLoop, () -> {
      if (connectionHeaderPreamble != null) {
        ReferenceCountUtil.safeRelease(connectionHeaderPreamble);
        connectionHeaderPreamble = null;
      }
      if (connectionHeaderWithLength != null) {
        ReferenceCountUtil.safeRelease(connectionHeaderWithLength);
        connectionHeaderWithLength = null;
      }
    });
  }
RPC connection implementation based on netty.
<p/>
Most operations are executed in handlers. Netty handler is always executed in the same
thread(EventLoop) so no lock is needed.
<p/>
<strong>Implementation assumptions:</strong> All the private methods should be called in the
{@link #eventLoop} thread, otherwise there will be races.
@since 2.0.0
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/NettyRpcConnection.java