Automatic detection and resolution of deadlocks in Go programs

The Go programming language is acquiring momentum in the development of concurrent software. Even though Go supports the shared-memory model, the message-passing alternative is the favoured idiomatic approach. Naturally, this practice is not exempt of the usual difficulties: programs may deadlock and the language run-time has only very basic support for deadlock detection. Previous research on deadlock detection mainly focused on shared-memory concurrency models. For mainstream languages, tools and approaches specific to the message-passing paradigm are scarce and incipient. There is however a large body of work on models of concurrency that only recently started to be applied to languages like Go. Since the Go run-time lets many deadlocks pass unnoticed, and the existing solutions provided by third party tools detect many deadlocks but only try to fix a limited set of specific patterns, imposing severe conditions to do so, there is a clear need for more general deadlock resolution strategies, going beyond prevention and avoidance. To gain insight on real-world deadlock bugs, we first built and categorized a collection of bugs sourced from high-profile open-source Go projects. Next, we extended and implemented an algorithm that takes an abstraction of the communication behaviour of the program and, when all the communication operations on channels necessary for progress are present, but a deadlock is possible, presents the problem and offers a possible resolution for the error. The extensions allows our approach to analyse a much wider range of real world programs. We conclude with an evaluation, comparing with two other state-of-the-art solutions.A linguagem de programação Go tem ganhado tração no desenvolvimento de software concorrente. Apesar de o Go suportar o modelo de partilha de memória, o modelo alternativo de partilha de mensagens é a abordagem idiomática. Naturalmente, esta prática não está isenta das dificuldades usuais: os programas podem bloquear e o runtime da linguagem só possui um suporte muito básico para a deteção destes bloqueios. Investigação anterior na deteção de bloqueios focou principalmente no modelo de partilha de memória. Para linguagens convencionais, ferramentas e abordagens dedicadas ao paradigma de passagem de mensagens são escassas e incipientes. No entanto, existe um grande conjunto de trabalhos sobre modelos de concorrência que só recentemente começou a ser aplicado em linguagens como o Go. Visto que o run-time do Go deixa muitos bloqueios passar despercebidos e as soluções existentes detetam muitos bloqueios, mas só tentam resolver um conjunto muito pequeno de padrões. De modo a ganhar conhecimento sobre erros de bloqueio reais, nós começámos por construir e categorizar uma coleção de erros obtidos a partir de projetos Go open-source de alto perfil. De seguida, nós estendemos e implementámos um algoritmo que recebe uma abstração do comportamento da comunicação de um programa e quando todas as operações de comunicação nos canais necessários para o progresso estão presentes, mas um bloqueio é possível, apresenta o erro e oferece uma possível resolução do erro. A nossa extensão permite analisar um conjunto muito maior de programas reais. Concluímos com uma avaliação, comparando com duas outras soluções do estado da arte

UPC-CHECK: A scalable tool for detecting run-time errors in Unified Parallel C

Unied Parallel C (UPC) is a language used to write parallel programs for shared and distributed memory parallel computers. UPC-CHECK is a scalable tool developed to automatically detect argument errors in UPC functions and deadlocks in UPC programs at run-time and issue high quality error messages to help programmers quickly x those errors. The tool is easy to use and involves merely replacing the compiler command with upc-check. The tool uses a novel distributed algorithm for detecting argument and deadlock errors in collective operations. The run-time complexity of the algorithm has been proven to be O(1). The algorithm has been extended to detect deadlocks created involving locks with a run-time complexity of O(T), where T is the number of threads waiting to acquire a lock. Error messages issued by UPC-CHECK were evaluated using the UPC RTED test suite for argument errors in UPC functions and deadlocks. Results of these tests show that the error messages issued by UPC-CHECK for these tests are excellent. The scalability of all the algorithms used was demonstrated using performance-evaluation test programs and the UPC NAS Parallel Benchmarks

Logic Simulation using an Asynchronous Parallel Discrete-Event Simulation Model on a SIMD Machine

The Chandy-Misra-Bryant (CMB) model has been applied to logic simulation of synchronous sequential circuits using a massively parallel SIMD computer, a CM-2 Connection Machine. Several methods of reducing message traffic in a logic simulation have been adapted to the SIMD architecture of the CM-2, with the result that each method of reducing message traffic actually decreases the speed of the simulation. This suggests that communication costs required to support logic simulation are small compared to the cost of deciding which messages need not be sent

Concurrent object-oriented programming: The MP-Eiffel approach

This article evaluates several possible approaches for integrating concurrency into object-oriented programming languages, presenting afterwards, a new language named MP-Eiffel. MP-Eiffel was designed attempting to include all the essential properties of both concurrent and object-oriented programming with simplicity and safety. A special care was taken to achieve the orthogonality of all the language mechanisms, allowing their joint use without unsafe side-effects (such as inheritance anomalies)