Why does Trajectory Execution Manager use MultiThreadedExecutor?

[CihatAltiparmak]

Description

While trying to integrate rmw_zenoh to MoveIt, i have seen that MoveGroup server uses MultiThreadedExecutor. rmw_zenoh doesn't work at the moment because of MultiThreadedExecutor. My aim here is not to report a bug, but to start a discussion about whether it's really necessary to use MultiThreadedExecutor here.

moveit2/moveit_ros/planning/trajectory_execution_manager/src/trajectory_execution_manager.cpp

Lines 193 to 201 in 9479604

	// The default callback group for rclcpp::Node is MutuallyExclusive which means we cannot call
	// receiveEvent while processing a different callback. To fix this we create a new callback group (the type is not
	// important since we only use it to process one callback) and associate event_topic_subscriber_ with this callback group
	auto callback_group = node_->create_callback_group(rclcpp::CallbackGroupType::MutuallyExclusive);
	auto options = rclcpp::SubscriptionOptions();
	options.callback_group = callback_group;
	event_topic_subscriber_ = node_->create_subscription<std_msgs::msg::String>(
	EXECUTION_EVENT_TOPIC, rclcpp::SystemDefaultsQoS(),
	[this](const std_msgs::msg::String::ConstSharedPtr& event) { return receiveEvent(event); }, options);

moveit2/moveit_ros/move_group/src/move_group.cpp

Lines 312 to 327 in 9479604

	rclcpp::executors::MultiThreadedExecutor executor;
	move_group::MoveGroupExe mge(moveit_cpp, default_planning_pipeline, debug);
	bool monitor_dynamics;
	if (nh->get_parameter("monitor_dynamics", monitor_dynamics) && monitor_dynamics)
	{
	RCLCPP_INFO(nh->get_logger(), "MoveGroup monitors robot dynamics (higher load)");
	planning_scene_monitor->getStateMonitor()->enableCopyDynamics(true);
	}
	planning_scene_monitor->publishDebugInformation(debug);
	mge.status();
	executor.add_node(nh);
	executor.spin();

Your environment

• ROS Distro: Rolling
• OS Version: Ubuntu 22.04
• Build Type: Source
• main
• rmw_zenoh