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This thesis presents a simple type system for expressing thread-locality in Java. Classes and types are annotated to express thread-locality and violations, where supposedly thread-local data may be shared between two or more threads, are detected at compile-time. The proposed system is an improvement over Loci, a minimal and modular type checker for expressing thread-locality in Java due to Wrigstad et al.

The improved Loci system presented in this thesis only adds an additional metadata annotation, four in total. We implemented the system as a command line tool that can be plugged into the standard javac compiler and used it to evaluate our design on a number of benchmarks.

We believe that Loci is compatible with how Java programs are written and that the improved system keeps the annotation overhead light while making it even simpler to treat a value as thread-local.