[QST] How to config xml to get multicast disable and data-sharing?

ZhenshengLee commented 2 years ago

Bug report

Required Info:

Operating System:
- ubuntu2204
Installation type:
- binary
Version or commit hash:
- humble
DDS implementation:
- fastdds
Client library (if applicable):
- rclcpp

Steps to reproduce issue

the source code is in https://github.com/ZhenshengLee/ros2_shm_msgs/tree/humble

# t0
colcon build
# t1
cd ./colcon/install/shm_msgs/lib
ros2 launch shm_msgs image_talker.launch.py
# t2
ros2 launch shm_msgs image_listener.launch.py

the fastdds xml is in the follow, which is not committed into the github reop, the xml is according https://fast-dds.docs.eprosima.com/en/latest/fastdds/ros2/ros2_configure.html#creating-ros-contexts-and-nodes https://fast-dds.docs.eprosima.com/en/latest/fastdds/transport/disabling_multicast.html#disabling-all-multicast-traffic https://discourse.ros.org/t/unconfigured-dds-considered-harmful-to-networks/25689/24

<?xml version="1.0" encoding="UTF-8"?>
<profiles xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
    <participant profile_name="participant_profile_ros2" is_default_profile="true">
        <rtps>
            <name>profile_for_ros2_context</name>
            <builtin>
                <metatrafficUnicastLocatorList>
                    <locator />
                </metatrafficUnicastLocatorList>
                <initialPeersList>
                    <locator>
                        <udpv4>
                            <address>127.0.0.1</address>
                        </udpv4>
                    </locator>
                </initialPeersList>
            </builtin>
        </rtps>
    </participant>
    <data_writer profile_name="default publisher profile" is_default_profile="true">
        <qos>
            <publishMode>
                <kind>ASYNCHRONOUS</kind>
            </publishMode>
            <data_sharing>
                <kind>AUTOMATIC</kind>
            </data_sharing>
        </qos>
        <historyMemoryPolicy>PREALLOCATED_WITH_REALLOC</historyMemoryPolicy>
    </data_writer>
    <data_reader profile_name="default subscription profile" is_default_profile="true">
        <qos>
            <data_sharing>
                <kind>AUTOMATIC</kind>
            </data_sharing>
        </qos>
        <historyMemoryPolicy>PREALLOCATED_WITH_REALLOC</historyMemoryPolicy>
    </data_reader>
</profiles>

Expected behavior

actually the image_talker.launch.py creates 8 image publisher processes.

So the ros2 graph should containe 8 nodes and the ros2cli should display

ros2 node list
ros2 topic list

Actual behavior

ros2 node list and ros2 topic list show the wrong info. the communication is abnormal

Additional information

the bug exist in galactic, in which the fastdds version is 2.3.2

Feature request

null

Implementation considerations

null

MiguelCompany commented 2 years ago

@ZhenshengLee

First, tag builtin should be inside tag rtps. Second, in order to achieve what you intend, you'll need to configure maxInitialPeersRange. See the note here

I've modified your XML with the necessary settings

<?xml version="1.0" encoding="UTF-8"?>
<profiles xmlns="http://www.eprosima.com/XMLSchemas/fastRTPS_Profiles">
    <transport_descriptors>
        <transport_descriptor>
            <transport_id>UDP_transport</transport_id>
            <type>UDPv4</type>
            <maxInitialPeersRange>10</maxInitialPeersRange>
        </transport_descriptor>
    </transport_descriptors>

    <participant profile_name="participant_profile_ros2" is_default_profile="true">
        <rtps>
            <name>profile_for_ros2_context</name>
            <userTransports>
                <transport_id>UDP_transport</transport_id>
            </userTransports>
            <useBuiltinTransports>false</useBuiltinTransports>

            <builtin>
                <metatrafficUnicastLocatorList>
                    <locator />
                </metatrafficUnicastLocatorList>
                <initialPeersList>
                    <locator>
                        <udpv4>
                            <address>127.0.0.1</address>
                        </udpv4>
                    </locator>
                </initialPeersList>
            </builtin>
        </rtps>
    </participant>

    <data_writer profile_name="default publisher profile" is_default_profile="true">
        <qos>
            <publishMode>
                <kind>ASYNCHRONOUS</kind>
            </publishMode>
            <data_sharing>
                <kind>AUTOMATIC</kind>
            </data_sharing>
        </qos>
        <historyMemoryPolicy>PREALLOCATED_WITH_REALLOC</historyMemoryPolicy>
    </data_writer>

    <data_reader profile_name="default subscription profile" is_default_profile="true">
        <qos>
            <data_sharing>
                <kind>AUTOMATIC</kind>
            </data_sharing>
        </qos>
        <historyMemoryPolicy>PREALLOCATED_WITH_REALLOC</historyMemoryPolicy>
    </data_reader>
</profiles>

ZhenshengLee commented 2 years ago

@MiguelCompany Thanks for your fast reply!

First, tag builtin should be inside tag rtps.

That's a typo in the issue page.

<name>profile_for_ros2_context</name>
            <userTransports>
                <transport_id>UDP_transport</transport_id>
            </userTransports>
            <useBuiltinTransports>false</useBuiltinTransports>

As in the docs, the data-sharing is a shared-memory-based function(but different from default shm transport) and is only available in intra-machine communication, so why should we use this config? Is data-sharing really working?

How to check if the data-sharing in working? I read from this the issue https://github.com/ros2/rmw_fastrtps/issues/579#issuecomment-1122709868 which suggest to check /dev/shm to see the mem files. But the shm(which is the default) transport also creates mem files in the same path. Is there a better way to check data-sharing function?

MiguelCompany commented 2 years ago

why should we use this config?

In order for the <maxInitialPeersRange> configuration to work, as it is configured as part of the transport.

How to check if the data-sharing in working?

Data-sharing related files start with prefix fast_datasharing, so ls /dev/shm/fast_datasharing* should work

ZhenshengLee commented 2 years ago

why should we use this config?

In order for the <maxInitialPeersRange> configuration to work, as it is configured as part of the transport.

How to check if the data-sharing in working?

Data-sharing related files start with prefix _fastdatasharing, so ls /dev/shm/fast_datasharing* should work

with the config xml above

default shm is enabled(check /dev/shm)
data-sharing is enabled when msg data type is POD(check /dev/shm)
multicast is disabled

It's tested and confirmed in https://github.com/ZhenshengLee/ros2_shm_msgs/tree/humble Thank you!

ros2 / rmw_fastrtps