[don't merge!] min reproducer for fast dds shm memory leak

[MichaelOrlov]

Description

• This PR is a Minimal Reproducer for the issue with the memory leak reported in the Memory "leak" #2366.

It adds two small executables in rosbag2_examples_cpp:

• byte_burst_publisher
• byte_subscriber_probe

Files:

• rosbag2_examples/rosbag2_examples_cpp/src/byte_burst_publisher.cpp
• rosbag2_examples/rosbag2_examples_cpp/src/byte_subscriber_probe.cpp

What they do

• byte_burst_publisher publishes:
  • many small messages on /small_topic, or
  • large std_msgs/msg/ByteMultiArray messages on /big_topic
  • optionally creates transient /many/t* topics to mimic topic churn from the original report
• byte_subscriber_probe is a minimal non-rosbag2 subscriber for /big_topic
  • it only subscribes
  • counts messages
  • reports the largest payload received
  • this is useful to check whether memory growth reproduces without rosbag2 in-process

Build

If example_interfaces is already available in your environment, just build rosbag2_examples_cpp.

source <your_ros_setup>/setup.bash
colcon build --packages-select rosbag2_examples_cpp

If example_interfaces is present in source but not installed in your current environment, build it first and source that prefix:

source /home/morlov/ros2_jazzy/install/setup.bash

colcon build \
  --packages-select example_interfaces \
  --base-paths /home/morlov/ros2_jazzy/src/ros2 \
  --build-base /tmp/example_interfaces_build \
  --install-base /tmp/example_interfaces_install

source /tmp/example_interfaces_install/setup.bash

colcon build \
  --packages-select rosbag2_examples_cpp \
  --base-paths /home/morlov/ros2_jazzy/src/ros2/rosbag2 \
  --build-base /tmp/rosbag2_examples_build \
  --install-base /tmp/rosbag2_examples_install

Run the minimal non-rosbag2 reproducer

Terminal 1, start the subscriber probe:

source /tmp/rosbag2_examples_install/setup.bash
source /tmp/example_interfaces_install/setup.bash

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
unset FASTDDS_BUILTIN_TRANSPORTS

ros2 run rosbag2_examples_cpp byte_subscriber_probe

Terminal 2, publish large messages in bursts:

source /tmp/rosbag2_examples_install/setup.bash
source /tmp/example_interfaces_install/setup.bash

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
unset FASTDDS_BUILTIN_TRANSPORTS

for i in 1 2 3 4 5; do
  ros2 run rosbag2_examples_cpp byte_burst_publisher --ros-args \
    -p mode:=big \
    -p big_mib:=10 \
    -p big_count:=20 \
    -p create_many_topics:=false
  sleep 2
done

In a third terminal, monitor RSS of the subscriber process:

watch -n 1 'ps -o pid,rss,cmd -C byte_subscriber_probe'

Compare RMW / transport behavior

Fast DDS with SHM enabled

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
unset FASTDDS_BUILTIN_TRANSPORTS

This is the configuration that reproduced the large RSS jump in testing.

Fast DDS with SHM disabled

export RMW_IMPLEMENTATION=rmw_fastrtps_cpp
export FASTDDS_BUILTIN_TRANSPORTS=UDPv4

This should keep RSS much flatter.

Cyclone DDS

export RMW_IMPLEMENTATION=rmw_cyclonedds_cpp
unset FASTDDS_BUILTIN_TRANSPORTS

This should also stay much flatter.

Optional rosbag2-style publisher behavior

To include transient /many/t* topic churn:

ros2 run rosbag2_examples_cpp byte_burst_publisher --ros-args \
  -p mode:=big \
  -p big_mib:=10 \
  -p big_count:=20 \
  -p create_many_topics:=true

To generate only the small-message stream:

ros2 run rosbag2_examples_cpp byte_burst_publisher --ros-args \
  -p mode:=small \
  -p small_count:=1000000

Expected result

The minimal subscriber reproducer is intended to show that:

• large-message memory growth can be observed without rosbag2 in-process
• the effect is much stronger with rmw_fastrtps_cpp + SHM enabled
• the effect is much smaller or flat with:
  • rmw_fastrtps_cpp + SHM disabled
  • rmw_cyclonedds_cpp

This helps separate rosbag2 behavior from middleware receive-path behavior.