During April 2025, this developer contributed to the facebook/folly repository by designing and implementing an atomic upsert operation, insert_or_assign_if, for the ConcurrentHashMap class. The feature enables safe insert-or-update semantics with a predicate check, reducing boilerplate and minimizing race conditions in high-concurrency scenarios. Developed in C++ with a focus on concurrency and data structures, the solution streamlines common upsert patterns by consolidating multiple operations into a single atomic step. The implementation was delivered in a dedicated commit and validated through targeted reviews and tests, enhancing the correctness and performance of folly’s concurrency primitives without requiring major bug fixes.