Implement Time Features in rclpy

[tfoote]

This ticket is to track rclpy specific time impelementation requirements

• implement a Clock on top of rcl implementation: Time, Duration, Clock wrapping rcl #209
• implement a TimeSource to implement the ROS2 time design: TimeSource and support for ROS time #210
  • use parameters for use_sim_time when now that parameters are available in rclpy. Respect the use_sim_time parameter for rclpy nodes #240
  • clock jump callbacks: Callbacks when time jumps #222
• upgrade Timer to use a Clock on top of rcl implementation
  • functionality using rcl clocks: create timer with clock #211
  • let users specify the clock to use: update this TODO Timer uses ROS time by default #419
• Implement a Rate method using the clock on top of rcl implementation (Add Rate #443)

[Nickolaim]

I can take this item if nobody is looking at it yet.

[tfoote]

I don't think anyone is actively working on this. If you'd like to start work on the clock, timer and rate that would be feasible. The time source is blocked on the availability of parameters. If you'd like to pick it up I'd suggest creating a separate ticket for one of the smaller parts to sketch out how you're going to approach it to get feedback before you jump in and implement it.

[dhood]

Here's some additional detail about the steps that would be required.

• Time class wrapping rcl types (rcl_time_point, rcl_duration) and functions (rcl_difference_times, rcl_get_time_now). Conversions to/from builtin_interfaces msg type.
• Clock class wrapping rcl's rcl_clock_t, exposing get_now; Node has a clock; demos using node.now() if appropriate.
• TimeSource wrapping rcl; implementation of ROS time support: A node is used to create a TimeSource of "ROS time" (subscription to /clock, use_sim_time support by some means), node's clock is managed by the TimeSource.
• Time jump types (TimeJump, JumpThreshold) and logic moved from rclcpp to rcl, wrapped in python. Jump handlers in python.
• Timer using specific Clock (rclpy Timer currently wraps an rcl timer that rcl_wait uses) in a similar manner to what will be done for rclcpp.
• Addition of Rate in a similar manner to what will be done for rclcpp.