protected final Call createSecurityPreambleCall(RpcCallback<Call> callback) {
    return new Call(-1, null, null, null, SecurityPreamableResponse.getDefaultInstance(), 0, 0,
      Collections.emptyMap(), callback, MetricsConnection.newCallStats());
  }
Does the clean up work after the connection is removed from the connection pool
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/RpcConnection.java