This is a prototype implementation of RCL for discussion about the thread configuration feature to receive and apply a set of scheduling parameters for the threads controlled by the ROS 2 executor.

Our basic idea is as below.
 1. Implement a new class rclcpp::thread and modify rclcpp to use it.
   This class has the same function set as the std::thread but also additional features to control its thread attributions.
 2. Modify the rcl layer to receive a set of scheduling parameters.
   The parameters are described in YAML format and passed via command line parameters, environment variables, or files.
 3. the rclcpp reads the parameters from rcl and applies them to each thread in the thread pool.

There have been some discussions about this pull request, as below.
[ROS Discourse]
https://discourse.ros.org/t/adding-thread-attributes-configuration-in-ros-2-framework/30701
[ROS 2 Real-Time Working Group]
ros-realtime/ros-realtime.github.io#18

Signed-off-by: Shoji Morita <s-morita@esol.co.jp>

…he pointing out below.

ros2/rclcpp#2205 (comment)

Signed-off-by: Shoji Morita <s-morita@esol.co.jp>

Signed-off-by: Shoji Morita <s-morita@esol.co.jp>

The modification of the interface is to go along with the
specification described in the draft REP shared in the thread below.

https://discourse.ros.org/t/adding-thread-attributes-configuration-in-ros-2-framework/30701/5

Signed-off-by: Shoji Morita <s-morita@esol.co.jp>

…e update of REP-2017 below.

ros-infrastructure/rep#385

Signed-off-by: Shoji Morita <s-morita@esol.co.jp>

Signed-off-by: Shoji Morita <s-morita@esol.co.jp>

…he thread below.

ros-infrastructure/rep#385 (comment)

Signed-off-by: Shoji Morita <s-morita@esol.co.jp>