Messages >0.5MB gets dropped occassionly when sent over SHM with QoS BEST_EFFORT

[dk-teknologisk-lag]

Hey everyone

I'm currently working with interfacing various sensors to a mobile robot using ROS2, where we experience message drops. I have recently created a issue here: ros2/rmw_fastrtps#739

But tried to go deeper and made small changes to the HelloWorldExample to use BEST_EFFORT and sending 10MB of messages.
It can be seen here

It seem to create SHM in /dev/shm, but only about 1MB. Also see the below screenshot for the samle lost callbacks, showing messages to be lost.

I'm on a recent master and its build an run in a ubuntu 22.04 docker container.

Are there any thing I can tune when its over SHM?

I have searched for similar discussions, but they are often referring to communication across network.

Thanks, Lars

[Barry-Xu-2018]

Maybe you should modify example HelloWorldExampleSharedMem which is used for shared memory.

[dk-teknologisk-lag]

Maybe you should modify example HelloWorldExampleSharedMem which is used for shared memory.

Ahh, didn't see that. I have done so.

[fujitatomoya]

@dk-teknologisk-lag FYI, there are a couple of things i want to point out.
CC: @MiguelCompany @Barry-Xu-2018 @EduPonz (correct me if i got anything wrong)

• there are 2 features which use shared memory. (both creates the files under /dev/shm file system.)

  1. shared memory transport, https://fast-dds.docs.eprosima.com/en/latest/fastdds/transport/shared_memory/shared_memory.html (i think you are dealing with this one only.)
  2. data sharing delivery, https://fast-dds.docs.eprosima.com/en/latest/fastdds/transport/datasharing.html

master...dk-teknologisk-lag:Fast-DDS:bestefforthelloworld

this uses std::string message type which is NOT bounded data type (Not PoD), that means this cannot use data sharing delivery. i think this is why @Barry-Xu-2018 introduced #4276 (comment)

Messages >0.5MB gets dropped occassionly when sent over SHM with QoS BEST_EFFORT

and comes back to the main title, this sounds possible.
since using Best Effort QoS setting, there is always the possibility to drop the message.

[fujitatomoya]

i think we can iterate on ros2/rmw_fastrtps#739 instead, so i will go ahead to close this discussion.