Start by clarifying requirements and edge cases, then design the ConnectionPool to manage a collection of DBConnection objects and track active connections. Implement PoolConnection as a wrapper that delegates query calls and returns itself to the pool on close. Discuss trade-offs like thread safety, connection reuse, and error handling.
Pro tip: Mention that you would use a thread-safe data structure (e.g., a queue with locks) to manage the pool, and consider adding a timeout or health check for idle connections to prevent stale connections.
Ask about thread safety, connection lifecycle, and expected usage patterns. Confirm that DBConnection cannot be modified and that PoolConnection should handle delegation and return-to-pool.
Decide on internal data structures: a pool of available connections and a count of active connections. Ensure get_connection returns None when max is reached, and that connections are reused.
Wrap a DBConnection instance, delegate query() to it, and on close(), return the underlying connection to the pool instead of closing it. Ensure close() is idempotent.
Use locks or thread-safe collections to manage pool access. Consider what happens if close() is called multiple times or if the pool is exhausted.
Talk about connection validation, timeouts, max lifetime, and metrics. Mention how this design supports scalability and resource management.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.