3,227 research outputs found
Locking Discipline Inference and Checking
Concurrency is a requirement for much modern software, but the implementation of multithreaded algorithms comes at the risk of errors such as data races. Programmers can prevent data races by documenting and obeying a locking discipline, which indicates which locks must be held in order to access which data. This paper introduces a formal semantics for locking specifications that gives a guarantee of race freedom. The paper also provides two implementations of the formal semantics for the Java language: one based on abstract interpretation and one based on type theory. To the best of our knowledge, these are the first tools that can soundly infer and check a locking discipline for Java. Our experiments com-pare the implementations with one another and with annotations written by programmers
PLACES'10: The 3rd Workshop on Programmng Language Approaches to concurrency and Communication-Centric Software
Paphos, Cyprus. March 201
Unlocking Blocked Communicating Processes
We study the problem of disentangling locked processes via code refactoring.
We identify and characterise a class of processes that is not lock-free; then
we formalise an algorithm that statically detects potential locks and propose
refactoring procedures that disentangle detected locks. Our development is cast
within a simple setting of a finite linear CCS variant \^a although it suffices
to illustrate the main concepts, we also discuss how our work extends to other
language extensions.Comment: In Proceedings WWV 2015, arXiv:1508.0338
Parameterized Concurrent Multi-Party Session Types
Session types have been proposed as a means of statically verifying
implementations of communication protocols. Although prior work has been
successful in verifying some classes of protocols, it does not cope well with
parameterized, multi-actor scenarios with inherent asynchrony. For example, the
sliding window protocol is inexpressible in previously proposed session type
systems. This paper describes System-A, a new typing language which overcomes
many of the expressiveness limitations of prior work. System-A explicitly
supports asynchrony and parallelism, as well as multiple forms of
parameterization. We define System-A and show how it can be used for the static
verification of a large class of asynchronous communication protocols.Comment: In Proceedings FOCLASA 2012, arXiv:1208.432
Type Inference for Deadlock Detection in a Multithreaded Polymorphic Typed Assembly Language
We previously developed a polymorphic type system and a type checker for a
multithreaded lock-based polymorphic typed assembly language (MIL) that ensures
that well-typed programs do not encounter race conditions. This paper extends
such work by taking into consideration deadlocks. The extended type system
verifies that locks are acquired in the proper order. Towards this end we
require a language with annotations that specify the locking order. Rather than
asking the programmer (or the compiler's backend) to specifically annotate each
newly introduced lock, we present an algorithm to infer the annotations. The
result is a type checker whose input language is non-decorated as before, but
that further checks that programs are exempt from deadlocks
Semantics for Locking Specifications
Lock-based synchronization disciplines, like Java\u2019s @GuardedBy, are widely used to prevent concurrency errors. However, their semantics is often expressed informally and is consequently ambiguous. This article highlights such ambiguities and overcomes them by formalizing two possible semantics of @GuardedBy, using a reference operational semantics for a core calculus of a concurrent Java-like language. It also identifies when such annotations are actual guarantees against data races. Our work aids in understanding the annotations and supports the development of sound tools that verify or infer them
Universes for Race Safety
Race conditions occur when two incorrectly synchronised threads simultaneously access the same object. Static type systems have been suggested to prevent them. Typically, they use annotations to determine the relationship between an object and its âguard â (another object), and to guarantee that the guard has been locked before the object is accessed. The object-guard relationship thus forms a tree similar to an ownership type hierarchy. Universe types are a simple form of ownership types. We explore the use of universe types for static identification of race conditions. We use a small, Java-like language with universe types and concurrency primitives. We give a type system that enforces synchronisation for all object accesses, and prove that race conditions cannot occur during execution of a type correct program. We support references to objects whose ownership domain is unknown. Unlike previous work, we do so without compromising the synchronisation strategy used where the ownership domain of such objects is fully known. We develop a novel technique for dealing with non-final (i.e. mutable) paths to objects of unknown ownership domain using effects
Compiling knowledge-based systems from KEE to Ada
The dominant technology for developing AI applications is to work in a multi-mechanism, integrated, knowledge-based system (KBS) development environment. Unfortunately, systems developed in such environments are inappropriate for delivering many applications - most importantly, they carry the baggage of the entire Lisp environment and are not written in conventional languages. One resolution of this problem would be to compile applications from complex environments to conventional languages. Here the first efforts to develop a system for compiling KBS developed in KEE to Ada (trademark). This system is called KATYDID, for KEE/Ada Translation Yields Development Into Delivery. KATYDID includes early prototypes of a run-time KEE core (object-structure) library module for Ada, and translation mechanisms for knowledge structures, rules, and Lisp code to Ada. Using these tools, part of a simple expert system was compiled (not quite automatically) to run in a purely Ada environment. This experience has given us various insights on Ada as an artificial intelligence programming language, potential solutions of some of the engineering difficulties encountered in early work, and inspiration on future system development
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