[image_tools] Cannot run cam2image and showimage with different RMW implementations

[jacobperron]

Bug report

Required Info:

• Operating System:
  • OSX High Sierra
• Installation type:
  • Binaries (Crystal prerelease)
• DDS implementation:
  • Connext + FastRTPS or Connext + Opensplice

Certain combinations of RMW implementations results in severe frame drops in image_tools demo. In particular, when Connext is involved.

Steps to reproduce issue

RMW_IMPLEMENTATION=rmw_fastrtps_cpp ros2 run image_tools showimage
# In another terminal
RMW_IMPLEMENTATION=rmw_connext_cpp ros2 run image_tools cam2image

or

RMW_IMPLEMENTATION=rmw_connext_cpp ros2 run image_tools showimage
# In another terminal
RMW_IMPLEMENTATION=rmw_opensplice_cpp ros2 run image_tools cam2image

Results in sporadic frames received.

---

RMW_IMPLEMENTATION=rmw_connext_cpp ros2 run image_tools showimage
# In another terminal
RMW_IMPLEMENTATION=rmw_fastrtps_cpp ros2 run image_tools cam2image

Results in a choppy video feed and we see this error repeated:

2018-12-13 15:25:07.491 [RTPS_WRITER Error] Cannot add DATA_FRAG submsg to the CDRMessage. Buffer too small -> Function add_data_frag
2018-12-13 15:25:07.491 [RTPS_WRITER Error] Error sending fragment (78, 5) -> Function send_any_unsent_changes

Expected behavior

No issues with receiving video frames running the examples across different RMW implementations.

Additional notes

There is no noted issues between FastRTPS and Opensplice.

Also, it seems that there is no issue with this combination:

RMW_IMPLEMENTATION=rmw_opensplice_cpp ros2 run image_tools showimage
# In another terminal
RMW_IMPLEMENTATION=rmw_connext_cpp ros2 run image_tools cam2image

[dirk-thomas]

This has been reported before: ros2/rmw_fastrtps#202. That ticket focused on addressing the FastRTPS performance itself - not the cross vendor performance.