Abstract. The design and implementation of a correct system can benefit from employing static techniques for ensuring that the dynamic behaviour satisfies the specification. Many programming languages incorporate types for ensuring that certain operations are only applied to data of the appropriate form. A natural extension of type checking techniques is to enrich the types with annotations and effects that further describe intensional aspects of the dynamic behaviour.

www.cs.bu.edu/fac/kfoury The Ambient Calculus was developed by Cardelli and Gordon as a formal framework to study issues of mobility and migrant code [CG98]. We consider an Ambient Calculus where ambients transport and exchange programs rather that just inert data. We propose different senses in which such a calculus can be said to be polymorphically typed, and design accordingly a polymorphic type system for it. Our type system assigns types to embedded programs and what we call behaviors to processes; a denotational semantics of behaviors is then proposed, here called trace semantics, underlying much of the remaining analysis. We state and prove a Subject Reduction property for our polymorphically-typed calculus. Based on techniques borrowed from finite automata theory, type-checking of fully type-annotated processes is shown to be decidable. Our polymorphically-typed calculus is a conservative extension of the typed Ambient Calculus originally proposed by Cardelli and Gordon [CG99].

After two decades of effort, type inference for dynamically typed languages scales to programs of a few tens of thousands of lines of code, but no further. For larger programs, this paper proposes using a kind of demand-driven analysis where the number of active goals is carefully restricted. To achieve this restriction, the algorithm occasionally prunes goals by giving them solutions that are trivially true and thus require no further subgoals to be solved; the previous subgoals of a newly pruned goal may often be discarded from consideration, reducing the total number of active goals. A specific algorithm DDP is described which uses this approach. An experiment on DDP shows that it infers precise types for roughly 30 % to 45 % of the variables in a program with hundreds of thousands of lines; the percentage varies with the choice of pruning threshold, a parameter of the algorithm. The time required varies from an average of one-tenth of one second per variable to an unknown maximum, again depending on the pruning threshold. These data suggest that 50 and 2000 are both good choices of pruning threshold, depending on whether speed or precision is more important.

Session types support a type-theoretic formulation of structured patterns of communication, so that the communication behaviour of agents in a distributed system can be verified by static type checking. Applications include network protocols, business processes, and operating system services. In this paper we define a multithreaded functional language with session types, which unifies, simplifies and extends previous work. There are four main contributions. First: an operational semantics with buffered channels, instead of the synchronous communication of previous work. Second: we prove that the session type of a channel gives an upper bound on the necessary size of the buffer. Third: session types are manipulated by means of the standard structures of a linear type theory, rather than by means of new forms of typing judgement. Fourth: a notion of subtyping, including the standard subtyping relation for session types (imported into the functional setting), and a novel form of subtyping between standard and linear function types which allows the typechecker to handle linear types conveniently. Our new approach significantly simplifies session types in the functional setting, clarifies their essential features, and provides a secure foundation for language developments such as polymorphism and object-orientation. 1

Visual tracking requires sophisticated algorithms working in real-time, and often spacelimited, settings. While the input streams may be regular in structure, the algorithms are not, and must often deal with probabilistic metrics. To ensure progress in algorithm design without incurring excessive development costs, we propose a high-level programming approach married with predictable and compositional performance metrics. This enables the combination of independently developed program components into coherent software architecture, with certified resource use guarantee. Here, we present our approach and discuss its application to the development and resource analysis of a space bound mean shift algorithm for motion tracking, using the new embedded system-oriented language Hume.

Abstract. There are many mechanisms for concurrency control in high-level programming languages. In Java, the original mechanism for concurrency control, based on synchronized blocks, is lexically scoped. For more flexible control, Java 5 introduced non-lexical operators, supporting lock primitives on re-entrant locks. These operators may lead to run-time errors and unwanted behavior; e.g., taking a lock without releasing it, which could lead to a deadlock, or trying to release a lock without owning it. This paper develops a static type and effect system to prevent the mentioned lock errors for non-lexical locks. The effect type system is formalized for an object-oriented calculus which supports non-lexical lock handling. Based on an operational semantics, we prove soundness of the effect type analysis. Challenges in the design of the effect type system are dynamic creation of threads, objects, and especially of locks, aliasing of lock references, passing of lock references between threads, and reentrant locks as found in Java. 1

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There are many mechanisms for concurrency control in high-level programming languages. In Java, the original mechanism for concurrency control, based on synchronized blocks, is lexically scoped. For more flexible control, Java 5 introduced non-lexical lock primitives on re-entrant locks. These operators may lead to runtime errors and unwanted behavior; e.g., taking a lock without releasing it, which could lead to a deadlock, or trying to release a lock without owning it. This paper develops a static type and effect system to prevent the mentioned lock errors for a formal, object-oriented calculus which supports non-lexical lock handling and exceptions. Based on an operational semantics, we prove soundness of the effect type analysis. Challenges in the design of the effect type system are dynamic creation of threads, objects, and especially of locks, aliasing of lock references, passing of lock references between threads, and reentrant locks as found in Java. Furthermore, the exception handling mechanism complicates the control-flow and thus the analysis.

Predicting the resources that are consumed by a program component is crucial for many parallel or distributed systems. In this context, the main resources of interest are execution time, space and communication/synchronisation costs. There has recently been significant progress in resource analysis technology, notably in type-based analyses and abstract interpretation. At the same time, parallel and distributed computing are becoming increasingly important. This paper synthesises progress in both areas to survey the state-of-the-art in resource analysis for parallel and distributed computing. We articulate a general model of resource analysis and describe parallel/distributed resource analysis together with the relationship to sequential analysis. We use three parallel or distributed resource analyses as examples and provide a critical evaluation of the analyses. We investigate why the chosen analysis is effective for each application and identify general principles governing