Assignment2 Chan Kai Wen

[kwchan03]

1. Addressed Component/Module/Part of the System
   Module: homeassistant/core.py
   Specific Part: The analysis focuses on the async_stop function, which was refactored from a monolithic block into a modular controller, and the async_start function, which was decorated by @log_execution_time for observability. These components control the critical startup and shutdown sequences of the Home Assistant Core.

2. Graph Created and Its Completeness
   I have selected a Call Graph to visualize the refactoring of async_stop and the application of the new decorator.

Graph Completeness:

This graph provides a complete representation of the reengineering effort because:

• It displays the new hierarchy where async_stop acts as a central controller, calling the five extracted helper functions: _can_stop, _async_shutdown_jobs, _async_stop_integrations, _async_final_write, and _async_close.
• It visualizes the @log_execution_time decorator attached to both async_start and async_stop, showing how observability was applied without modifying internal logic.
• It maps exactly how the new helper functions interact with the existing functions (set_state, async_fire_internal). The edges are labeled with parameters (STOPPING, NOT_RUNNING), verifying that the original shutdown sequence and logic remain intact.

3. Impact and Insights Gained From The Analysis
   The Call Graph analysis highlights three key structural improvements:

• Decomposed Complexity: The graph visually confirms that the complexity of async_stop has been drastically lowered. The main controller is now a simple linear sequence calling five helper nodes, rather than a monolithic block containing all logic.
• Fault Isolation: The analysis proves that failure domains are now distinct. If the system hangs, the graph allows us to trace the stall to a specific leaf node (e.g., _async_stop_integrations waiting on async_block_till_done) without debugging unrelated code in other stages.
• Verified Sequence of Events: The graph confirms that the critical order of operations is preserved. It visualizes exactly when state changes occur, ensuring that resources are shut down in the correct order before the system fully closes.