Virtual Machine Support for Many-Core Architectures: Decoupling Abstract from Concrete Concurrency Models

The upcoming many-core architectures require software developers to exploit concurrency to utilize available computational power. Today's high-level language virtual machines (VMs), which are a cornerstone of software development, do not provide sufficient abstraction for concurrency concepts. We analyze concrete and abstract concurrency models and identify the challenges they impose for VMs. To provide sufficient concurrency support in VMs, we propose to integrate concurrency operations into VM instruction sets. Since there will always be VMs optimized for special purposes, our goal is to develop a methodology to design instruction sets with concurrency support. Therefore, we also propose a list of trade-offs that have to be investigated to advise the design of such instruction sets. As a first experiment, we implemented one instruction set extension for shared memory and one for non-shared memory concurrency. From our experimental results, we derived a list of requirements for a full-grown experimental environment for further research

Full Issue: Volume 13, Issue 1 - Winter 2018

Full Issue: Volume 13, Issue 1 - Winter 201

Performance Analysis and Modelling of Concurrent Multi-access Data Structures

The major impediment to scaling concurrent data structures is memory contention when accessing shared data structure access-points, leading to thread serialisation, hindering parallelism. Aiming to address this challenge, significant amount of work in the literature has proposed multi-access techniques that improve concurrent data structure parallelism. However, there is little work on analysing and modelling the execution behaviour of concurrent multi-access data structures especially in a shared memory setting. In this paper, we analyse and model the general execution behaviour of concurrent multi-access data structures in the shared memory setting. We study and analyse the behaviour of the two popular random access patterns: shared (Remote) and exclusive (Local) access, and the behaviour of the two most commonly used atomic primitives for designing lock-free data structures: Compare and Swap, and, Fetch and Add. We model the concurrent multi-accesses by splitting the thread execution procedure into five logical sessions: i) side-work, ii) access-point search iii) access-point acquisition, iv) access-point data acquisition and v) access-point data operation. We model the acquisition of an access-point, as a system of closed queuing networks with parallel servers, and data acquisition in terms of where the data is located within the memory system. We evaluate our model on a set of concurrent data structure designs including a counter, a stack and a FIFO queue. The evaluation is carried out on two state of the art multi-core processors: Intel Xeon Phi CPU 7290 with 72 physical cores and Intel Xeon E5-2695 with 14 physical cores. Our model is able to predict the throughput performance of the given concurrent data structures with 80% to 100% accuracy on both architectures

Continuous ASL perfusion fMRI investigation of higher cognition: Quantification of tonic CBF changes during sustained attention and working memory tasks

Arterial spin labeling (ASL) perfusion fMRI is an emerging method in clinical neuroimaging. Its non-invasiveness, absence of low frequency noise, and ability to quantify the absolute level of cerebral blood flow (CBF) make the method ideal for longitudinal designs or low frequency paradigms. Despite the usefulness in the study of cognitive dysfunctions in clinical populations, perfusion activation studies to date have been conducted for simple sensorimotor paradigms or with single-slice acquisition, mainly due to technical challenges. Using our recently developed amplitude-modulated continuous ASL (CASL) perfusion fMRI protocol, we assessed the feasibility of a higher level cognitive activation study in twelve healthy subjects. Taking advantage of the ASL noise properties, we were able to study tonic CBF changes during uninterrupted 6-min continuous performance of working memory and sustained attention tasks. For the visual sustained attention task, regional CBF increases (6–12 ml/100 g/min) were detected in the right middle frontal gyrus, the bilateral occipital gyri, and the anterior cingulate/medial frontal gyri. During the 2-back working memory task, significantly increased activations (7–11 ml/100 g/min) were found in the left inferior frontal/precentral gyri, the left inferior parietal lobule, the anterior cingulate/medial frontal gyri, and the left occipital gyrus. Locations of activated and deactivated areas largely concur with previous PET and BOLD fMRI studies utilizing similar paradigms. These results demonstrate that CASL perfusion fMRI can be successfully utilized for the investigation of the tonic CBF changes associated with high level cognitive operations. Increased applications of the method to the investigation of cognitively impaired populations are expected to follow

On the set of certain conflicts of a given language

Two concurrent processes are said to be in conflict if they can get trapped in a situation where they both are waiting or running endlessly, forever unable to complete their common task. In the design of reactive systems, this is a common fault which can be very subtle and hard to detect. This paper studies conflicts in more detail and characterises the most general set of behaviours of a process which certainly leads to a conflict when accepted by another process running in parallel. It shows how this set of certain conflicts can be used to simplify the automatic detection of conflicts and thus the verification of reactive systems

An automatic abstraction technique for verifying featured, parameterised systems

A general technique combining model checking and abstraction is presented that allows property based analysis of systems consisting of an arbitrary number of featured components. We show how parameterised systems can be specified in a guarded command form with constraints placed on variables which occur in guards. We prove that results that hold for a small number of components can be shown to scale up. We then show how featured systems can be specified in a similar way, by relaxing constraints on guards. The main result is a generalisation theorem for featured systems which we apply to two well known examples

Multimodal Image Analysis of Chronic Leukemic Lymphoproliferative Disorders and the Hypothesis of »Single« and »Multiple« Programmed Stops in the Development of Typical and Atypical Forms of Leukemias and Lymphomas

The study consisted of morphometric analysis, assessment of the argyrophilic nucleolar organization region (AgNOR) characteristics, and image cytometry (ICM) in different tumor mass compartments: bone marrow (BM), peripheral blood (PB) and lymph nodes (LN) from patients with chronic leukemic lymphoproliferative disorders. A total of 71895 cells were analyzed on SFORM PC (VAMSTEC, Zagreb). Correlation between morphometric, AgNOR and ICM characteristics revealed the cells with low proliferative activity to possess small, homogeneous AgNOR, with the majority of cells in the peak of DNA histogram. The cells with high proliferative activity had inhomogeneous AgNOR, mostly containing greater DNA content than peak cells, pathologic mitoses (DNA>4N), or the majority of cells were in the S-phase of the cell cycle. Cells with medium proliferative activity and annular AgNOR were in-between. Analysis of different tumor mass compartments showed that lymphatic cells with the affinity to accumulate in BM regularly exhibited low proliferative activity (a lower percentage of cells in SFC and highest percentage of cells in the peak of the G0/G1 phase). The cells in LN exhibited the characteristics of proliferative cells (an increased number of AgNOR, larger and more proliferative inhomogeneous AgNOR, and lowest percentage of cells in the G0/G1 phase). The migration of cells from BM to LN and between lymph nodes occurred through PB (there were cells with low and high proliferative activity: a higher proportion of cells in SFC and at the same time in the G0/G1 phase of the cell cycle). Analysis of cell size and proliferative activity in different compartments of tumor mass revealed that the cells in BM and PB did not differ substantially according to size and proliferative activity, while an inverse pattern was observed between PB and LN. As small cells are inactive and larger cells more proliferative, the analysis quite unexpectedly showed the PB cells to be largest and most inactive, in contrast to LN where the cells were smallest and most active. The »single« and »multiple programmed stops« have been hypothesized in the development of typical forms of leukemias and lymphomas and atypical forms of subacute and subchronic leukemias. Differentiation impairment may occur at any stage, and different »stop« locations result in different morphology and affinity to accumulation in bone marrow, peripheral blood and lymph nodes

Culture as Non-Consensus: Exploring Coherence Among Native Speakers’ Perceptions of German Expressions of Affection

From early in their learning experience, foreign language (FL) learners at American universities explore socio-cultural connotations that, it is argued, are signified by FL words. Textbook authors and teachers follow an implicit canon of difference, a list of iconic words that over time—and without the benefit of empirical evidence—have come to represent essential differences in outlook between their native and the FL culture (Kubota, 2004). Despite the fast progression of the theory of teaching culture in FL learning (Kramsch, 2015; Risager, 2015), large empirical gaps remain. Todate, there is little evidence that native speakers (NSs) of the FL perceive their cultural practices, including the cultural contexts in which language is used, homogenously enough to warrant their status as cultural traits. Using the example of expressions of affection, this exploratory study drew on qualitative and quantitative questionnaire data to investigate whether German NSs’ (N=52) accounts of their own and of most fellow Germans’ language behavior converged enough to derive a comprehensive and reliable cultural norm. Results indicated a lack of consensus among German NSs’ self-reported views, eluding the assumption of a pertinent community-specific norm. Implications for FL teaching and learning, as well as directions for future research, are discussed