ros2-assignments/doc/architecture/nodes/RetakeGradeDeterminator.md

RetakeGradeDeterminator (assignments::one::retake_grade_determinator)

Overview

The RetakeGradeDeterminator node handles the processing of retake exams for students who have failed courses. It provides a ROS2 action server that accepts retake requests, manages exam result collection for retake scenarios, and coordinates with the grade calculator service to determine final retake grades.

Implementation Details

Parameters

• grade_collection_amount (int, default: 5): Number of exam results required before triggering grade calculation for a retake student-course combination.

Constructor

RetakeGradeDeterminator(std::unique_ptr<DatabaseManager> db_manager = nullptr)

• Initializes ROS2 node with name retake_grade_determinator
• Sets up DatabaseManager (optional injection for testing)
• Creates publisher for student course management
• Subscribes to exam results topic with retake-specific callback
• Initializes service client for grade calculation
• Creates ROS2 action server for retake requests with reentrant callback group

Core Functions

void exam_results_callback(const g2_2025_interfaces::msg::Exam::SharedPtr msg)

• Only processes exam results when retake_allowed_ flag is true
• Triggers grade calculation request when threshold is met

void grade_calculator_request(StudentCourse combo)

• Waits for grade calculator service to be available
• Sends async request with collected retake exam grades

void grade_calculator_response(rclcpp::Client<g2_2025_interfaces::srv::Exams>::SharedFuture future, StudentCourse studentCourseCombo)

• Clears collected exam data from internal map
• Updates retake status in database for the student-course combination
• Publishes final student message to ROS2 topic with timestamp
• Stores final course result in database with retake flag set to true

Action Server Callbacks

rclcpp_action::GoalResponse goal_callback(const rclcpp_action::GoalUUID& uuid, std::shared_ptr<const g2_2025_interfaces::action::Retake::Goal> goal)

• Accepts retake goal requests for specific student-course combinations
• Logs received retake requests with student and course information
• Returns ACCEPT_AND_EXECUTE for all valid requests

rclcpp_action::CancelResponse cancel_callback(const std::shared_ptr<rclcpp_action::ServerGoalHandle<g2_2025_interfaces::action::Retake>> goal_handle)

• Handles retake action cancellation requests
• Returns ACCEPT for all cancellation requests

void spawn_callback_thread(const std::shared_ptr<rclcpp_action::ServerGoalHandle<g2_2025_interfaces::action::Retake>> goal_handle)

• Creates detached thread for asynchronous retake action execution
• Ensures non-blocking retake processing

void async_execute_callback_thread(const std::shared_ptr<rclcpp_action::ServerGoalHandle<g2_2025_interfaces::action::Retake>> goal_handle)

• Enables retake exam processing by setting retake_allowed_ flag
• Publishes student enrollment message to trigger exam generation
• Creates and returns successful action result