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Abstract. The Universe Type System is an ownership type system for object-oriented programming languages that hierarchically structures the object store; it is used to reason modularly about programs. We formalise Universe Types for a core subset of Java in two steps: We first define a Topological Type System that structures the object store hierarchically into an ownership tree, and demonstrate soundness of the Topological Type System by proving subject reduction. Motivated by concerns of modular verification, we then present an Encapsulation Type System that enforces the owner-as-modifier discipline; that is, that object updates are initiated by the owner of the object. The contributions of this paper are, firstly, an extensive type-theoretic account of the Universe Type System, with explanations and complete proofs, and secondly, the clean separation of the topological from the encapsulation concerns.

Atomicity provides strong guarantees against errors caused by unanticipated thread interactions, but is difficult for programmers to implement with low-level concurrency primitives. With the introduction of multicore processors, the problems are compounded. Atomic sections are a high level language feature that programmers can use to designate the blocks of code that need to be free from unanticipated thread interactions, letting the language implementation handle the low-level details such as deadlock. From a language designer's point of view, the challenge is to implement atomic sections without compromising performance.We propose an implementation of atomic sections that inserts locks transparently into object-oriented programs. The main advantages of our approach are: (1) We infer path expressions (that at run-time resolve to actual objects) for many more accesses in the atomic section than previous work could infer. (2) We use multi-granularity locking for guarding iterative traversals. (3) We ensure freedom from deadlock by rolling back the lock acquisition phase. (4) We release locks as early as possible. In summary, our approach uses a finer-grained locking discipline than previous lock inference techniques.

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