On the Behaviour of General-Purpose Applications on Cloud Storages

Managing data over cloud infrastructures raises novel challenges with respect to existing and well studied approaches such as ACID and long running transactions. One of the main requirements is to provide availability and partition tolerance in a scenario with replicas and distributed control. This comes at the price of a weaker consistency, usually called eventual consistency. These weak memory models have proved to be suitable in a number of scenarios, such as the analysis of large data with Map-Reduce. However, due to the widespread availability of cloud infrastructures, weak storages are used not only by specialised applications but also by general purpose applications. We provide a formal approach, based on process calculi, to reason about the behaviour of programs that rely on cloud stores. For instance, one can check that the composition of a process with a cloud store ensures `strong' properties through a wise usage of asynchronous message-passing

Destructive pneumococcal septic arthritis in end-stage renal disease

Summary: Pneumococcal arthritis generally presents as non-destructive monoarthritis, although some underlying metabolic disorders such as liver failure and diabetes have been suggested to represent a risk factor for severe joint disease. Here we report a case of destructive pneumococcal arthritis of the left hip joint in a patient suffering from chronic renal failure treated with hemodialysis for ten years. Inspite of effective anti-pneumococcal antibiotic treatment, the patient with pre-existing renal osteopathy and a mild osteoarthritis continued to suffer from severe and disabling pain of the left hip. This case demonstrates that pneumococcal joint infection in patients with underlying uremic bone disease can lead to quick deterioration of the affected join

Linguistic terrioriality under stress:European perspectives

This article revisits a well-known dichotomy (the ‘territorial’ and ‘personal’ principles) and develops a four-element classification of state approaches(from the most generous to the most menacing, from the perspective of speakers of minority languages). The article examines the implications for language policy of geographically dispersed or spatially concentrated patterns of distribution of speakers of particular languages. We begin by exploring the general literature on language policy, focusing in particular on the territorial and personal principles, the use of ‘threshold rules’ at municipal and other subnational levels, and the hybrid language regimes that are often a consequence of sociolinguistic complexity. We consider the extent to which responses to linguistic diversity across Europe may be understood by reference to these principles and categories. We explain why we have selected particular case studies (the Baltic republics, Transylvania, Switzerland, Belgium and Ireland) for further exploration. We conclude that, notwithstanding the value of the typologies we consider, real-life cases are almost invariably more complex, with states implementing policies that defy categorisation, that may change over time, and that may treat different language minorities by reference to different principles

Reasoning algebraically about refinement on TSO architectures

The Total Store Order memory model is widely implemented by modern multicore architectures such as x86, where local buffers are used for optimisation, allowing limited forms of instruction reordering. The presence of buffers and hardware-controlled buffer flushes increases the level of non-determinism from the level specified by a program, complicating the already difficult task of concurrent programming. This paper presents a new notion of refinement for weak memory models, based on the observation that pending writes to a process' local variables may be treated as if the effect of the update has already occurred in shared memory. We develop an interval-based model with algebraic rules for various programming constructs. In this framework, several decomposition rules for our new notion of refinement are developed. We apply our approach to verify the spinlock algorithm from the literature

Robustness against Power is PSPACE-complete

Power is a RISC architecture developed by IBM, Freescale, and several other companies and implemented in a series of POWER processors. The architecture features a relaxed memory model providing very weak guarantees with respect to the ordering and atomicity of memory accesses. Due to these weaknesses, some programs that are correct under sequential consistency (SC) show undesirable effects when run under Power. We call these programs not robust against the Power memory model. Formally, a program is robust if every computation under Power has the same data and control dependencies as some SC computation. Our contribution is a decision procedure for robustness of concurrent programs against the Power memory model. It is based on three ideas. First, we reformulate robustness in terms of the acyclicity of a happens-before relation. Second, we prove that among the computations with cyclic happens-before relation there is one in a certain normal form. Finally, we reduce the existence of such a normal-form computation to a language emptiness problem. Altogether, this yields a PSPACE algorithm for checking robustness against Power. We complement it by a matching lower bound to show PSPACE-completeness

Locality and Singularity for Store-Atomic Memory Models

Robustness is a correctness notion for concurrent programs running under relaxed consistency models. The task is to check that the relaxed behavior coincides (up to traces) with sequential consistency (SC). Although computationally simple on paper (robustness has been shown to be PSPACE-complete for TSO, PGAS, and Power), building a practical robustness checker remains a challenge. The problem is that the various relaxations lead to a dramatic number of computations, only few of which violate robustness. In the present paper, we set out to reduce the search space for robustness checkers. We focus on store-atomic consistency models and establish two completeness results. The first result, called locality, states that a non-robust program always contains a violating computation where only one thread delays commands. The second result, called singularity, is even stronger but restricted to programs without lightweight fences. It states that there is a violating computation where a single store is delayed. As an application of the results, we derive a linear-size source-to-source translation of robustness to SC-reachability. It applies to general programs, regardless of the data domain and potentially with an unbounded number of threads and with unbounded buffers. We have implemented the translation and verified, for the first time, PGAS algorithms in a fully automated fashion. For TSO, our analysis outperforms existing tools

Verifying linearizability on TSO architectures

Linearizability is the standard correctness criterion for fine-grained, non-atomic concurrent algorithms, and a variety of methods for verifying linearizability have been developed. However, most approaches assume a sequentially consistent memory model, which is not always realised in practice. In this paper we define linearizability on a weak memory model: the TSO (Total Store Order) memory model, which is implemented in the x86 multicore architecture. We also show how a simulation-based proof method can be adapted to verify linearizability for algorithms running on TSO architectures. We demonstrate our approach on a typical concurrent algorithm, spinlock, and prove it linearizable using our simulation-based approach. Previous approaches to proving linearizabilty on TSO architectures have required a modification to the algorithm's natural abstract specification. Our proof method is the first, to our knowledge, for proving correctness without the need for such modification

Influence of anthropometric parameters and biochemical markers of bone metabolism on quantitative ultrasound of bone in the institutionalized elderly

The assessment of bone quality by quantitative ultrasound (QUS), a transportable and relatively cheap method, shows some correlations with bone mineral density (BMD) as measured by dual-energy X-ray absorptiometry (DXA) and with fracture risk. To examine its correlation with bone metabolism in a population of institutionalized elderly people known to be at high risk for vitamin D deficiency and secondary hyperparathyroidism, QUS of the calcaneus and biochemical parameters were measured in 264 women aged 85±7 (SD) years and in 103 men aged 81±8 years living in 19 nursing homes. Vitamin D deficiency was frequent in this population: 41.9% of the women and 31.4% of the men had a serum 25-hydroxyvitamin (25OHD) level below the 2.5th percentile level of 3276 normal Swiss adults (6.2 µg/l or 15.5 mmol/l). Hyperparathyroidism was less frequent: serum parathyroid hormone (PTH) levels were above the 97.5th percentile level of normal adults (70 pg/l) in 18.9% of women and 9.8% of men. In women, QUS data correlated significantly with age (r=−0.297), body mass index (BMI) (r=0.403), calcium (r=0.220), PTH (r=−0.296), 25OHD (r=0.298) and alkaline phosphatase (AP) (r=−0.170) for broadband ultrasound attenuation (BUA), and with age (r=−0.195), BMI (r=0.208), PTH (r=−0.174), 25OHD (r=0.140) and AP (r=−0.130) for speed of sound (SOS). In men, ultrasound data correlated with BMI (r=0.326), calcium (r=0.199), 25OHD (r=0.258) and AP (r=−0.311) for BUA, and with AP (r=−0.196) for SOS. In women, but not in men because of their smaller number, a multivariate analysis was performed to examine relationships between age, BMI, biochemical markers and QUS. Age, BMI, PTH and phosphate explained 30% of the variance of BUA and 10% for SOS. In conclusion, QUS of bone evaluates characteristics of bone that are influenced, at least partially, by age, BMI and the secondary hyperparathyroidism due to vitamin D deficienc