Today’s shared-memory parallel programming models are complex and error-prone. While many parallel programs are intended to be deterministic, unanticipated thread interleavings can lead to subtle bugs and nondeterministic semantics. In this paper, we demonstrate that a practical type and effect system can simplify parallel programming by guaranteeing deterministic semantics with modular, compile-time type checking even in a rich, concurrent object-oriented language such as Java. We describe an object-oriented type and effect system that provides several new capabilities over previous systems for expressing deterministic parallel algorithms. We also describe a language called Deterministic Parallel Java (DPJ) that incorporates the new type system features, and we show that a core subset of DPJ is sound. We describe an experimental validation showing that DPJ can express a wide range of realistic parallel programs; that the new type system features are useful for such programs; and that the parallel programs exhibit good performance gains (coming close to or beating equivalent, nondeterministic multithreaded programs where those are available).

chinwn,davidcri,nguyenh2© Conventional specifications for object-oriented (OO) programs must adhere to behavioral subtyping in support of class inheritance and method overriding. However, this requirement inherently weakens the specifications of overridden methods in superclasses, leading to imprecision during program reasoning. To address this, we advocate a fresh approach to OO verification that focuses on the distinction and relation between specifications that cater to calls with static dispatching from those for calls with dynamic dispatching. We formulate a novel specification subsumption that can avoid code re-verification, where possible. Using a predicate mechanism, we propose a flexible scheme for supporting class invariant and lossless casting. Our aim is to lay the foundation for a practical verification system that is precise, concise and modular for sequential OO programs. We exploit the separation logic formalism to achieve this.

Abstract. The dynamic frames approach has proven to be a powerful formalism for specifying and verifying object-oriented programs. However, it requires writing and checking many frame annotations. In this paper, we propose a variant of the dynamic frames approach that eliminates the need to explicitly write and check frame annotations. Reminiscent of separation logic’s frame rule, programmers write access assertions inside pre- and postconditions instead of writing frame annotations. From the precondition, one can then infer an upper bound on the set of locations writable or readable by the corresponding method. We implemented our approach in a tool, and used it to automatically verify several challenging programs, including subject-observer, iterator and linked list. 1

Abstract. Separation logic is a Hoare-style logic for reasoning about programs with heap-allocated mutable data structures. As a step toward extending separation logic to high-level languages with ML-style general (higher-order) storage, we investigate the compatibility of nested Hoare triples with several variations of higher-order frame rules. The interaction of nested triples and frame rules can be subtle, and the inclusion of certain frame rules is in fact unsound. A particular combination of rules can be shown consistent by means of a Kripke model where worlds live in a recursively defined ultrametric space. The resulting logic allows us to elegantly prove programs involving stored code. In particular, it leads to natural specifications and proofs of invariants required for dealing with recursion through the store. Keywords. Higher-order store, Hoare logic, separation logic, semantics. 1

{kevin.bierhoff,nbeckman,jonathan.aldrich} @ cs.cmu.edu. Reusable APIs often define usage protocols. We previously developed a sound modular type system that checks compliance with typestate-based protocols while affording a great deal of aliasing flexibility. We also developed Plural, a prototype tool that embodies our approach as an automated static analysis and includes several extensions we found useful in practice. This paper evaluates our approach along the following dimensions: (1) We report on experience in specifying relevant usage rules for a large Java standard API with our approach. We also specify several other Java APIs and identify recurring patterns. (2) We summarize two case studies in verifying third-party open-source code bases with few false positives using our tool. We discuss how tool shortcomings can be addressed either with code refactorings or extensions to the tool itself.

Abstract. Object invariants define the consistency of objects. They have subtle semantics, mainly because of call-backs, multi-object invariants, and subclassing. Several verification techniques for object invariants have been proposed. It is difficult to compare these techniques, and to ascertain their soundness, because of their differences in restrictions on programs and invariants, in the use of advanced type systems (e.g., ownership types), in the meaning of invariants, and in proof obligations. We develop a unified framework for such techniques. We distil seven parameters that characterise a verification technique, and identify sufficient conditions on these parameters which guarantee soundness. We instantiate our framework with three verification techniques from the literature, and use it to assess soundness and compare expressiveness. 1

Abstract. We adapt a variant of permission-accounting separation logic to a concurrent Java-like language with fork/join. To support both concurrent reads and information hiding, we combine fractional permissions with abstract predicates. As an example, we present a separation logic contract for iterators that prevents data races and concurrent modifications. Our program logic is presented in an algorithmic style: we avoid structural rules for Hoare triples and formalize logical reasoning about typed heaps by natural deduction rules and a set of sound axioms. We show that verified programs satisfy the following properties: data race freedom, absence of null-dereferences and partial correctness.

The method of logical relations is a classic technique for proving the equivalence of higher-order programs that implement the same observable behavior but employ different internal data representations. Although it was originally studied for pure, strongly normalizing languages like System F, it has been extended over the past two decades to reason about increasingly realistic languages. In particular, Appel and McAllester’s idea of step-indexing has been used recently to develop syntactic Kripke logical relations for MLlike languages that mix functional and imperative forms of data abstraction. However, while step-indexed models are powerful tools, reasoning with them directly is quite painful, as one is forced to engage in tedious step-index arithmetic to derive even simple results. In this paper, we propose a logic LADR for equational reasoning about higher-order programs in the presence of existential type abstraction, general recursive types, and higher-order mutable state. LADR exhibits a novel synthesis of features from Plotkin-Abadi logic, Gödel-Löb logic, S4 modal logic, and relational separation logic. Our model of LADR is based on Ahmed, Dreyer, and Rossberg’s state-of-the-art step-indexed Kripke logical relation, which was designed to facilitate proofs of representation independence for “state-dependent ” ADTs. LADR enables one to express such proofs at a much higher level, without counting steps or reasoning about the subtle, step-stratified construction of possible worlds.

We present the first complete soundness proof of the antiframe rule, a recently proposed proof rule for capturing information hiding in the presence of higher-order store. Our proof involves solving a non-trivial recursive domain equation. It helps identify some of the key ingredients for soundness, and thereby suggests how one might hope to relax some of the restrictions imposed by the rule.

Interactive programs, such as GUIs or spreadsheets, often maintain dependency information over dynamically-created networks of objects. That is, each imperative object tracks not only the objects its own invariant depends on, but also all of the objects which depend upon it, in order to notify them when it changes. These bidirectional linkages pose a serious challenge to verification, because their correctness relies upon a global invariant over the object graph. We show how to modularly verify programs written using dynamically-generated bidirectional dependency information. The critical idea is to distinguish between the footprint of a command, and the state whose invariants depends upon the footprint. To do so, we define an application-specific semantics of updates, and introduce the concept of a ramification operator to explain how local changes can alter our knowledge of the rest of the heap. We illustrate the applicability of this style of proof with a case study from functional reactive programming, and formally justify reasoning about an extremely imperative implementation as if it were pure.