ROS2 listener not entering the callback function

edit

I am interfacing a ROS2 subscriber with a native RTI DDS publisher.

I have the following message structure for the message named DetectedObjectList

int16 id

//an array of objects of another message type

DetectedObject[ ] objects

and the DetectedObject.msg is defined as follows :

int16 id

int16 x

int16 y

I am publishing an id and an object of type DetectedObject

To Simplify the problem, now my msg file contains only int16 id.

If I look at the RTI Admin Console, the datatypes in the ROS2 listener and RTI are matched and everything seems to be ok.

I feel I am doing something wrong in the ROS2 listener node. Here is the snippet for my ROS2 listener

EDIT : Full ROS2 code.

import sys
import rclpy
from rclpy.node import Node

from openadx_msg.msg import (DetectedObjectList, DetectedObject)

class DemoNode(Node):

    def __init__(self):
        super().__init__('ros2_listener')
        self.sub = self.create_subscription(DetectedObjectList, 'vehicle/objects', self.object_callback)

    def object_callback(self,msg):
        print("entering callback")
        log = self.get_logger().info
        log('Received a message')
        log('id: {}.format(msg.id)')

def main(args=None):
    if args is None:
        args=sys.argv
    node=DemoNode()    // EDIT2
    rclpy.spin(node)

    node.destroy_node()
    rclpy.shutdown()

if __name__=='__main__':  //EDIT3
    main()

Here is the code for the RTI DDS python connector :

from __future__ import print_function
from ctypes import *
import sys
import os
from sys import path as sysPath
from os import path as osPath
from time import sleep
import math
filepath = osPath.dirname(osPath.realpath(__file__))
sysPath.append(filepath + "/../../../")
import rticonnextdds_connector as rti

def main():


    connector = rti.Connector("MyParticipantLibrary::Zero",
                          filepath + "/../ROS2_demo_nodes_py.xml")
    outputDDS = connector.getOutput("MyPublisher::VehicleObjectWriter")


    for i in range(1,50000):


            outputDDS.instance.setNumber("id_",i)
            outputDDS.write()

            toPrint = "id_ : " + repr(i)
            print(toPrint)





if __name__== "__main__":
    main()

And here is the xml file used by this connector. The xml is a translated version of the ROS2 IDL file.

<dds xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="http://community.rti.com/schema/5.1.0/rti_dds_profiles.xsd" version="5.1.0">

    <!-- Qos Library -->
    <qos_library name="QosLibrary">
        <qos_profile name="DefaultProfile" is_default_qos="true" base_name="BuiltinQosLib::Generic.510TransportCompatibility">
            <datawriter_qos>
                <property>
                    <value>
                        <element>
                        <name>dds.data_writer.history.memory_manager.fast_pool.pool_buffer_max_size</name>
                        <value>2147483647</value>
                        </element>
                    </value>
                </property>
            </datawriter_qos>

            <datareader_qos>
                <property>
                    <value>
                        <element>
                        <name>dds.data_writer.history.memory_manager.fast_pool.pool_buffer_max_size</name>
                        <value>2147483647</value>
                        </element>
                    </value>
                </property>
            </datareader_qos>
            <publisher_qos>
                <partition>
                    <name>
                        <element>rt/vehicle</element>
                    </name>
                </partition>
            </publisher_qos>
            <subscriber_qos>
                <partition>
                    <name>
                        <element>rt/vehicle</element>
                    </name>
                </partition>
            </subscriber_qos>
            <participant_qos>
                <transport_builtin>
                    <mask>UDPV4 | SHMEM</mask>
                </transport_builtin>
            </participant_qos>
        </qos_profile>
    </qos_library>

    <!-- types -->
    <types>
    <module name="openadx_msgs">
    <module name="msg">
    <module name="dds_">
      <const name="VehicleControl__GEAR_KEEP" type="int32" value="-1"/>
      <const name="VehicleControl__GEAR_PARK" type="int32" value="0"/>
      <const name="VehicleControl__GEAR_NEUTRAL" type="int32" value="1"/>
      <const name="VehicleControl__GEAR_DRIVE" type="int32" value="2"/>
      <const name="VehicleControl__GEAR_REVERSE" type="int32" value="3"/>
      <struct name= "VehicleControl_">
        <member name="accelerator_pedal_" type="float64"/>
        <member name="brake_pedal_" type="float64"/>
        <member name="steering_wheel_" type="float64"/>
        <member name="gear_" type="int32"/>
      </struct>
    </module>
    </module>
    </module>

    <module name="openadx_msgs">
    <module name="msg">
    <module name="dds_">
     <struct ...