Worked on improving the reliability of the Postgres-backed messaging path in the spring-integration repository, focusing on a critical concurrency issue. Addressed a race condition in the PostgresSubscribableChannel unsubscription logic by introducing a ReentrantReadWriteLock to synchronize the hasHandlers state, ensuring correct handler management during concurrent operations. Developed a dedicated test to reproduce and verify the fix, demonstrating a test-driven approach to concurrency challenges. Utilized Java and PostgreSQL within the Spring Integration framework to enhance the stability of message subscriptions, reducing issues related to race conditions during unsubscribe, polling, and dispatch. The work emphasized correctness and robust synchronization patterns.