Intra_process_demo is not zero-copy if doing external communications as well

[AlexisTM]

Bug report

Intra process communication has a

Required Info:

• Operating System:
  • Ubuntu 18.04
• Installation type:
  • Binairies
• Version or commit hash:
  • c9e55acba6eaf377ccacce844853fd9eb20d1113
• DDS implementation:
  • Fast-RTPS
• Client library:
  • rclcpp

Steps to reproduce issue

• Run ros2 run intra_process_demo two_node_pipeline
• Experience zero-copy (received object address == published object address)
• Run ros2 topic echo number
• The received object doesn't have the same address as the published one anymore

Expected behavior

I expect the received object address to always be the published object address even when also subscribing to the topic externally.

Actual behavior

The received object has been copied.

Additional information

NOTE: The object is reallocated to the same address in the lambda function

NOTE: The Published address when listening is equal to the last received address; Due to allocation optimization?

$ ros2 run intra_process_demo two_node_pipeline
Published message with value: 0, and address: 0x563E68561220
 Received message with value: 0, and address: 0x563E68561220
Published message with value: 1, and address: 0x563E68561220
 Received message with value: 1, and address: 0x563E68561220
Published message with value: 2, and address: 0x563E68561220
 Received message with value: 2, and address: 0x563E68561220
Published message with value: 3, and address: 0x563E68561220
 Received message with value: 3, and address: 0x563E68561220
Published message with value: 4, and address: 0x563E68561220
 Received message with value: 4, and address: 0x563E68561220
Published message with value: 5, and address: 0x563E68561220
 Received message with value: 5, and address: 0x563E68561220
Published message with value: 6, and address: 0x563E68561220
 Received message with value: 6, and address: 0x563E68561220
Published message with value: 7, and address: 0x563E68561220
 Received message with value: 7, and address: 0x563E68561220
Published message with value: 8, and address: 0x563E68561220
 Received message with value: 8, and address: 0x563E685D29D0
Published message with value: 9, and address: 0x563E685D29D0
 Received message with value: 9, and address: 0x563E68561220
Published message with value: 10, and address: 0x563E68561220
 Received message with value: 10, and address: 0x563E685D29D0
Published message with value: 11, and address: 0x563E685D29D0
 Received message with value: 11, and address: 0x563E68561220
Published message with value: 12, and address: 0x563E68561220
 Received message with value: 12, and address: 0x563E68561220

$ ros2 topic echo number
data: 8
---
data: 9
---
data: 10
---
data: 11
---

[hidmic]

@AlexisTM what rclcpp version are you running against?

[AlexisTM]

ros-dashing-rclcpp/bionic,now 0.7.11-1bionic.20191016.192455 amd64 [installed,automatic]

[hidmic]

Alright, yeah, I see the problem. I'll open an issue on rclcpp, to assess whether to hotfix or backport (as this is fixed in Eloquent). Thanks for reporting!

[AlexisTM]

Closing in favor of: ros2/rclcpp#912