Intensional Effect Polymorphism

Type-and-effect systems are a powerful tool for program construction and verification. We describe intensional effect polymorphism, a new foundation for effect systems that integrates static and dynamic effect checking. Our system allows the effect of polymorphic code to be intensionally inspected through a lightweight notion of dynamic typing. When coupled with parametric polymorphism, the powerful system utilizes runtime information to enable precise effect reasoning, while at the same time retains strong type safety guarantees. We build our ideas on top of an imperative core calculus with regions. The technical innovations of our design include a relational notion of effect checking, the use of bounded existential types to capture the subtle interactions between static typing and dynamic typing, and a differential alignment strategy to achieve efficiency in dynamic typing. We demonstrate the applications of intensional effect polymorphism in concurrent programming, security, graphical user interface access, and memoization

PLACES'10: The 3rd Workshop on Programmng Language Approaches to concurrency and Communication-Centric Software

Paphos, Cyprus. March 201

Formal foundations for hybrid effect analysis

Type-and-effect systems are a powerful tool for program construction and verification. Type-and-effect systems are useful because it can help reduce bugs in computer programs, enable compiler optimizations and also provide sort of program documentation. As software systems increasingly embrace dynamic features and complex modes of compilation, static effect systems have to reconcile over competing goals such as precision, soundness, modularity, and programmer productivity. In this thesis, we propose the idea of combining static and dynamic analysis for effect systems to improve precision and flexibility. We describe intensional effect polymorphism, a new foundation for effect systems that integrates static and dynamic effect checking. Our system allows the effect of polymorphic code to be intensionally inspected. It supports a highly precise notion of effect polymorphism through a lightweight notion of dynamic typing. When coupled with parametric polymorphism, the powerful system utilizes runtime information to enable precise effect reasoning, while at the same time retains strong type safety guarantees. The technical innovations of our design include a relational notion of effect checking, the use of bounded existential types to capture the subtle interactions between static typing and dynamic typing, and a differential alignment strategy to achieve efficiency in dynamic typing. We introduce the idea of first-class effects, where the computational effect of an expression can be programmatically reflected, passed around as values, and analyzed at run time. A broad range of designs “hard-coded in existing effect-guided analyses can be supported through intuitive programming abstractions. The core technical development is a type system with a couple of features. Our type system provides static guarantees to application-specific effect management properties through refinement types, promoting “correct-by-design effect-guided programming. Also, our type system computes not only the over-approximation of effects, but also their under-approximation. The duality unifies the common theme of permission vs. obligation in effect reasoning. Finally, we show the potential benefit of intensional effects by applying it to an event-driven system to obtain safe concurrency. The technical innovations of our system include a novel effect system to soundly approximate the dynamism introduced by runtime handlers registration, a static analysis to precompute the effects and a dynamic analysis that uses the precomputed effects to improve concurrency. Our design simplifies modular concurrency reasoning and avoids concurrency hazards

Open Effects: Optimistic Effects for Dynamic Dispatch

The open world assumption in modern object-oriented languages makes the design of a type-and-effect system challenging. The main problem is with the computation of the effects of a dynamically dispatched method call, because all possible dynamic types are not known in advance. We show that the open world assumption and the need for a type-and-effect system can be reconciled. We propose open effects, an optimistic effect assumed to satisfy the effect-based property of interest. We describe a sound type-and-effect system with open effects which has two parts: a static part that takes effects of dynamically dispatched calls with certain special references as open effects; and a dynamic part that manages dynamic effects as these special references change and verifies that the optimistic assumptions about open effects hold. This system is implemented in the Open-JDK compiler, and its utility is tested by applying it to verify noninterference of concurrent tasks

Designing with Static Capabilities and Effects: Use, Mention, and Invariants (Pearl)

Capabilities (whether object or reference capabilities) are fundamentally tools to restrict effects. Thus static capabilities (object or reference) and effect systems take different technical machinery to the same core problem of statically restricting or reasoning about effects in programs. Any time two approaches can in principle address the same sets of problems, it becomes important to understand the trade-offs between the approaches, how these trade-offs might interact with the problem at hand. Experts who have worked in these areas tend to find the trade-offs somewhat obvious, having considered them in context before. However, this kind of design discussion is often written down only implicitly as comparison between two approaches for a specific program reasoning problem, rather than as a discussion of general trade-offs between general classes of techniques. As a result, it is not uncommon to set out to solve a problem with one technique, only to find the other better-suited. We discuss the trade-offs between static capabilities (specifically reference capabilities) and effect systems, articulating the challenges each approach tends to have in isolation, and how these are sometimes mitigated. We also put our discussion in context, by appealing to examples of how these trade-offs were considered in the course of developing prior systems in the area. Along the way, we highlight how seemingly-minor aspects of type systems - weakening/framing and the mere existence of type contexts - play a subtle role in the efficacy of these systems

Open Effects: Programmer-guided Effects for Open World Concurrent Programs

The open world assumption makes the design of a type-and-effect system challenging, especially in concurrent object-oriented languages. The main problem is in the computation of the effects of a dynamically dispatched method invocation, because all possible dynamic types of its receiver are not known statically. Previous work proposes effect annotations that provide a static upper bound on the effects of a dynamically dispatched method, conservative enough to cover the effects of all methods which could possibly be executed upon its invocation. For two dynamically dispatched methods, a typical type-and-effect system may disallow concurrent execution of their invocations because their conservatively specified static effects conflict. However, such a conflict may not actually happen at runtime, depending on the dynamic types of their receivers. This work proposes open effects, a sound trust-but-verify type-and-effect system, to better enable concurrent execution of dynamically dispatched method invocations. If a programmer annotates the receiver of a certain method invocation as open, then the type system trusts the programmer and assigns an open effect to the method. The open effect is supposed, optimistically, not to conflict with other effects. Such optimistic assumptions are verified statically, if possible, or at runtime otherwise. Open effects is complementary to previously proposed static and dynamic effect analyses and combines them such that the accuracy of static analysis could help decrease the overhead of the dynamic analysis. Performance evaluations of an implementation of open effects, on various benchmarks, show that: open effects incurs negligible annotation and runtime overheads such that code with open effects does almost as well as its manually tuned concurrent version

A Parallel Mesh-Adaptive Framework for Hyperbolic Conservation Laws

We report on the development of a computational framework for the parallel, mesh-adaptive solution of systems of hyperbolic conservation laws like the time-dependent Euler equations in compressible gas dynamics or Magneto-Hydrodynamics (MHD) and similar models in plasma physics. Local mesh refinement is realized by the recursive bisection of grid blocks along each spatial dimension, implemented numerical schemes include standard finite-differences as well as shock-capturing central schemes, both in connection with Runge-Kutta type integrators. Parallel execution is achieved through a configurable hybrid of POSIX-multi-threading and MPI-distribution with dynamic load balancing. One- two- and three-dimensional test computations for the Euler equations have been carried out and show good parallel scaling behavior. The Racoon framework is currently used to study the formation of singularities in plasmas and fluids.Comment: late submissio

Open Effects

Open world assumption is an important design decision for modern object-oriented languages --- it allows extensibility in program design. Type-and-effect systems are also valuable for these languages, e.g. they can help reason about concurrent OO programs. Open world assumption, however, makes the design of a type-and-effect system challenging for an OO language. Main problem is with the computation of the effects of a dynamically dispatched method call, because all possible dynamic types are not known in advance. Previous research has proposed asking programmers for effect annotations that give an upper bound on the effects of a dynamically dispatched method call. This work describes an easier approach for programmers, albeit with some runtime overhead compared to previous work, which is based on the novel notion of open effects, effects that are optimistically assumed to satisfy the effect-based property of interest. We describe a sound type-and-effect system with open effects which has two parts: a static part that takes effects of dynamically dispatched calls with certain special references as an open effect; and a dynamic part that manages dynamic effects as these special references change and verifies that the optimistic assumptions about open effects hold. This system is implemented in the OpenJDK compiler and its utility is tested by applying it to verify non(interference) of concurrent tasks