Internet of Things (IoT) software should provide good support for IoT devices as IoT devices are growing in quantity and complexity. Communication between IoT devices is largely realized in a concurrent way. How to ensure the correctness of concurrent access becomes a big challenge to IoT software development. This paper proposes a general refactoring framework for fine-grained read–write locking and implements an automatic refactoring tool to help developers convert built-in monitors into fine-grained ReentrantReadWriteLocks. Several program analysis techniques, such as visitor pattern analysis, alias analysis, and side-effect analysis, are used to assist with refactoring. Our tool is tested by several real-world applications including HSQLDB, Cassandra, JGroups, Freedomotic, and MINA. A total of 1072 built-in monitors are refactored into ReentrantReadWriteLocks. The experiments revealed that our tool can help developers with refactoring for ReentrantReadWriteLocks and save their time and energy.