Safety Verification of Phaser Programs

We address the problem of statically checking control state reachability (as in possibility of assertion violations, race conditions or runtime errors) and plain reachability (as in deadlock-freedom) of phaser programs. Phasers are a modern non-trivial synchronization construct that supports dynamic parallelism with runtime registration and deregistration of spawned tasks. They allow for collective and point-to-point synchronizations. For instance, phasers can enforce barriers or producer-consumer synchronization schemes among all or subsets of the running tasks. Implementations %of these recent and dynamic synchronization are found in modern languages such as X10 or Habanero Java. Phasers essentially associate phases to individual tasks and use their runtime values to restrict possible concurrent executions. Unbounded phases may result in infinite transition systems even in the case of programs only creating finite numbers of tasks and phasers. We introduce an exact gap-order based procedure that always terminates when checking control reachability for programs generating bounded numbers of coexisting tasks and phasers. We also show verifying plain reachability is undecidable even for programs generating few tasks and phasers. We then explain how to turn our procedure into a sound analysis for checking plain reachability (including deadlock freedom). We report on preliminary experiments with our open source tool

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

Paphos, Cyprus. March 201

Programming multicores safely : handling barrier deadlocks

Tese de doutoramento, Informática (Ciências da Computação), Universidade de Lisboa, Faculdade de Ciências, 2015Nowadays, most produced computing devices include multicore processors. Applications that run on these devices only scale if they can compute in parallel. To this end, mainstream programming languages, like Java and C♯, adopted various parallel programming techniqffes. his thesis focffses on a parallel technique, called barrier, used for synchronisation. A barrier coordinates the execution order of parallel activities, by letting them wait for each other. Tasks using barriers are susceptible to the problem of deadlocks, where at least two activities are (indirectly) in a stalemate because of a conflicting ordering of some barriers. Deadlocks are a class of concurrency failures with a big impact in parallel programs. To help make parallel programming more productive, we propose two complementary techniques that handle deadlocks caused by barriers: a runtime verification tool, and a deadlock-free programming model. We present Armus, a runtime verification tool specialised in barrier deadlocks that is distributed, fault-tolerant, and verifies X10 and Java programs. Our technique verifies more barrier synchronisation patterns than existing state-of-the-art techniques. We improve deadlock verification based on graph analysis: our technique selects from two alternative graph representations of concurrency dependencies to hasten deadlock checking. Armus is evaluated with three benchmark suites in local and distributed scenarios. To handle barrier deadlocks at design time we propose a language called SBrenner that extends and formalises a programming model that originates from the Habanero-Java and the X10 languages. The outcome is a deadlock-free programming model that leverages pipeline parallelism. We present an operational semantics and a type system for SBrenner. Offr type system enjoys the properties of progress and subject reduction.Actualmente, a generalidade dos dispositivos de computação inclui um processador multicore. As aplicações que correm em processadores muIticore só aumentam o seu desempenho se computarem em paralelo, aproveitando assim o poder computacional dos núcleos disponíveis. Para este efeito, as linguagens de programação mais populares, tal como Java e C♯, adoptaram, nos últimos anos, várias técnicas de programação paralela. Esta tese lida com uma classe de falhas que origina da utilização de uma técnica de programação paralela, chamada barreira, cuja funcionalidade é a de sincronizar grupos de tarefas. Uma barreira coordena a ordem de execução de um grupo de tarefas, disponibilizando um ponto de execução em que as várias tarefas dum grupo podem esperar umas pelas outras. As tarefas que usam barreiras são vulneráveis ao problema de impasse, em que pelo menos duas tarefas estão (indirectamente) à espera uma da outra em barreiras diferentes sem que qualquer uma das tarefas possa avançar. Os impasses constituem uma classe de falhas, da área de concorrência, com grande impacto em programas paralelos. O nosso objectivo é aumentar a produtividade da programação paralela tratando do problema de impasses em barreiras. Nesta tese propomos duas técnicas complementares para lidar com o problema de impasses: uma ferramenta de verificação especializada em impasses sobre barreiras que é distribuída, tolerante a falhas e verifica aplicações X10 e Java; um modelo de programação isento de impasses

Static deadlock detection for concurrent go by global session graph synthesis

© 2016 ACM.Go is a programming language developed at Google, with channelbased concurrent features based on CSP. Go can detect global communication deadlocks at runtime when all threads of execution are blocked, but deadlocks in other paths of execution could be undetected. We present a new static analyser for concurrent Go code to find potential communication errors such as communication mismatch and deadlocks at compile time. Our tool extracts the communication operations as session types, which are then converted into Communicating Finite State Machines (CFSMs). Finally, we apply a recent theoretical result on choreography synthesis to generate a global graph representing the overall communication pattern of a concurrent program. If the synthesis is successful, then the program is free from communication errors. We have implemented the technique in a tool, and applied it to analyse common Go concurrency patterns and an open source application with over 700 lines of code

Space Shuttle main engine turbopump bearing assessment program

This report documents the work done on the bearing assessment program over the past two and a half years. The objective of the program is to develop a nondestructive evaluation system for the SSME HPOTP's which would be used to detect anomalies in installed bearings without engine disassembly. Data bases of various signatures are obtained by slowly turning the pump shafts before and after an engine firing. These signatures are then analyzed and compared to the original signatures to more accurately predict bearing wear

Millisecond cryo-trapping by the spitrobot crystal plunger simplifies time-resolved crystallography

We introduce the spitrobot, a protein crystal plunger, enabling reaction quenching via cryo-trapping with millisecond time-resolution. Canonical micromesh loops are mounted on an electropneumatic piston, reactions are initiated via the liquid application method (LAMA), and finally intermediate states are cryo-trapped in liquid nitrogen. We demonstrate binding of several ligands in microcrystals of three enzymes, and trapping of reaction intermediates and conformational changes in macroscopic crystals of tryptophan synthase