Images coming in bursts using reliable QoS

[sloretz]

Bug report

Required Info:

• Operating System:
  • Ubuntu Bionic
• Installation type:
  • Eloquent Debs

• Version or commit hash:

  ros-eloquent-connext-cmake-module/bionic,bionic,now 0.8.2-1bionic.20191109.000408 amd64 [installed,automatic]
  ros-eloquent-rmw-connext-cpp/bionic,bionic,now 0.8.1-1bionic.20191113.152945 amd64 [installed]
  ros-eloquent-rmw-connext-shared-cpp/bionic,bionic,now 0.8.1-1bionic.20191113.152740 amd64 [installed,automatic]
  ros-eloquent-rosidl-typesupport-connext-c/bionic,bionic,now 0.8.2-1bionic.20191113.152811 amd64 [installed,automatic]
  ros-eloquent-rosidl-typesupport-connext-cpp/bionic,bionic,now 0.8.2-1bionic.20191113.152616 amd64 [installed,automatic]
  rti-connext-dds-5.3.1/bionic,bionic,bionic,bionic,now 5.3.1-nc.x64Linux3gcc5.4.0+2 amd64 [installed,automatic]
  

• DDS implementation:
  • RTI Connext
• Client library (if applicable):
  • rclcpp

Steps to reproduce issue

Publish images using Connext over a topic using reliable for the reliability QoS setting

First terminal

export RMW_IMPLEMENTATION=rmw_connext_cpp
. /opt/ros/eloquent/setup.bash
ros2 run image_tools showimage

Second terminal

export RMW_IMPLEMENTATION=rmw_connext_cpp
. /opt/ros/eloquent/setup.bash
ros2 run image_tools cam2image

Repeat the same test using best effort reliability

first terminal

ros2 run image_tools showimage --ros-args -p reliability:=best_effort

second terminal

ros2 run image_tools cam2image --ros-args -p reliability:=best_effort

Expected behavior

Since this is localhost communication, all messages should be received quickly by the subscriber using either QoS setting

Actual behavior

Using reliable reliability the messages received at the subscriber are delayed by several seconds, and they seem to arrive in batches.

When using best effort the messages are received by the subscriber with very little delay, as expected.

Additional information

Possibly related to #302