Intra-Process Communications for all language clients

[emersonknapp]

Description

This issue is a call for a design of zero-copy intra-process communications available to all ROS2 language clients.

The current implementation of this feature exists in rclcpp and therefore is not usable for Python (or less-supported languages C, Java, Rust, etc.)

Acceptance Criteria

To close this issue, we want a design document that proposes the architecture for

• Intra-process optimized communications
• zero copy
• Available to all ROS2 language clients (therefore exists at or below the level of rcl)

As a follow up, will attempt to collect existing thoughts from https://github.com/ros2/design/pull/239 and add as comments below.

Note

I do not consider myself personally an expert on this, however I'm very interested in collaborating towards a top down view of what this part of the ROS2 core should look like, and figuring out how the community can pull together towards a solution