4.1. Designing a Thread-safe Class

While it is possible to write a thread-safe program that stores all its state in public static fields, it is a lot harder to verify its thread safety or to modify it so that it remains thread-safe than one that uses encapsulation appropriately. Encapsulation makes it possible to determine that a class is thread-safe without having to examine the entire program.

The design process for a thread-safe class should include these three basic elements: Identify the variables that form the object’s state; Identify the invariants that constrain the state variables; Establish a policy for managing concurrent access to the object’s state.